**2. Experimental and clinical essentials of preventative and therapeutic probiotic use in AD**

As briefly mentioned above, there is a good experimental and clinical theoretical basis for using probiotics in the prevention and therapy of AD. Germ-free animal models demonstrate that bacterial gut colonization is essential for maturation of immune function and induction of oral tolerance. It has been proposed that a similar but more subtle process may be occurring in human beings with progressively cleaner environments. Probiotic intestinal flora is arguably the most abundant source of early immune stimulation and contributes significantly to microbial burden in early life. A number of studies have suggested differences in the early colonization patterns of infants who go on to develop allergic disease. These studies strongly suggest that the pattern of colonization in the first weeks of life may influence the patterns of immune development [19,20]. These notions have been supported by observations that gut flora can influence local and systemic immune responses. There has been speculation that intestinal flora may influence the maturing precursor cells that circulate through the gut before they home to other tissues. This may explain how probiotic species can influence systemic immune responses and IgA production in distal sites, such as the respiratory tract. Together with reported clinical effects in early allergic disease, this has logically led to a growing interest in the role of probiotics in allergy prevention [13,14].

The gastrointestinal tract of the newborn baby is sterile. Soon after birth, however, it is colonized by many different microorganisms. Colonization is complete after around one week, but the numbers and species of intestinal bacteria fluctuate markedly during the first

The Role of Probiotics in Atopic Dermatitis Prevention and Therapy 357

Probiotic intestinal flora contributes to microbial antigen exposure in early life and is one of the most abundant sources of early immune stimulation. Because allergic immune responses manifest early in life, there has been obvious interest in the potential benefits of modifying the gastrointestinal flora by using probiotic supplementation. However, the value of probiotics for primary prevention is controversial [13,14]. So far, there have been only several studies to address the role of probiotics in primary prevention, with a reported suspicious reduction in the incidence of eczema. The role of probiotics in allergy prevention has remained controversial, and there has been an urgent call for similar studies to address this further. This chapter will try to highlight the issues with probiotics in the therapy / prevention of AD and future of this therapy. Here, firstly newly described mechanisms of probiotic effects will be defined. Later, under the light of recent literature probiotic use in

**2.1 Experimental (animal) and clinical (human) studies showing mechanisms of** 

effect of probiotics in various experimental and clinical atopic disease models.

**2.1.1 Maturing gut barrier: Probiotic regulation in intestinal epithelium and** 

and fecal α-1-antitrypsin levels as well as an increase in fecal IgA level [23].

intestinal permeability and to enhance frequently defective IgA responses [33].

Although the beneficial effects of probiotics on wide variety of atopic diseases have been suggested, little is known about how probiotics modulate the immune system and atopic disease development. Currently, only limited publications are available defining the effects of probiotics in murine or human models of AD. Therefore, it is important to explore the

Recent data indicate that commensal intestinal microbiota represents a major modulator of intestinal homeostasis. Dysregulation of the symbiotic interaction between intestinal microbiota and the mucosa may result in a pathological condition with potential clinical repercussions. For instance, it is shown that mice reared in germ-free conditions have an underdeveloped immune system and have no oral tolerance. In contrast, pathogen-free mice are capable of reconstituting the bacterial flora with Bifidobacteria and tolerance

In addition to providing maturational signals for the gut-associated lymphoid tissue, probiotics balance the generation of pro- and anti-inflammatory cytokines in the gut. After probiotic consumption, decrease in fecal α-1 antitrypsin, serum TNF-α, and changes in TGFβ and other cytokines point to down-regulation of inflammatory mediators [28]. For instance, after a challenge study in infants allergic to cow's milk, fecal IgA levels were detected to be higher and TNF-α levels were lower in the Lctbs rhamnosus GG (LGG) applied group compared to the placebo [29]. Similarly, another study by Kirjavainen et al suggested that Bfdbm lactis Bb12 might modify gut microflora to alleviate early onset atopic eczema. And this modification was found to be compatible with reductions of serum TNF-α

Moreover, probiotic bacteria may counteract the inflammatory process by stabilizing the gut microbial environment and the permeability barrier of the intestine, and by enhancing the degradation of enteral antigens and altering their immunogenicity [30]. This gut-stabilizing effect of probiotics could be explained by the improvement by probiotics of the immunological barrier of the intestine through intestinal IgA responses, specifically [31,32]. Consistent with these explanations, in children with food allergies, probiotics are shown to reverse increased

AD therapy and prevention is being discussed in detail.

**probiotics` effects in atopic diseases including eczema** 

**upregulation of host immune responses** 

development [27].

several months of life. The composition of the gut microbiota differs between healthy and allergic infants and even in countries with a high and low prevalence of allergies [21]. Mode of delivery, either vaginal or through caesarean section, also has a major impact on early colonization patterns of the infant gut [4]. In the case of allergy, the rationale for modulating the intestinal microbiota is supported by observations that allergic children have a different microbiota composition than healthy infants. The main changes associated with allergic trait are less frequent colonization with Lactobacilli and lower counts of Bifidobacteria [9,22]. In addition to these quantitative differences in the Bfdbm microbiota, qualitative differences have also been observed. Infants with AD have been found to have a more adult type Bfdbm microbiota with high prevalence of Bfdbm adolescentis. Healthy infants, on the other hand, were found to be colonized mainly by Bfdbm bifidum, typical for breast-fed infants [7,8]. The Bifidobacteria from infants with AD were found to induce a higher secretion of proinflammatory cytokines in vitro, whereas the Bifidobacteria from healthy infants induced the secretion of more antiinflammatory cytokines. Also, Bifidobacteria of dairy origin stimulated more antiinflammatory and less inflammatory cytokines than Bifidobacteria from allergic infants. In addition to differing in their induction of cytokines, Bifidobacteria from allergic and healthy infants also exhibited different in vitro adhesion to Caco-2 tissue culture cells and intestinal mucus. This difference in adhesion to the intestinal mucosa may result in a different or reduced stimulation of the immune system through the gut-associated lymphoid tissue [23]. Lower counts of Bifidobacteria have been reported in atopic vs nonatopic children preceding allergen sensitization. Bifidobacteria are hypothesized to more effectively promote tolerance to nonbacterial antigens, primarily by inhibiting the development of a Th2-type (proallergic) response. In a recent study, a positive change in stool colonization in atopic infants supplemented with Bfdbm lactis has been shown with a decrease of Bacteroides and E coli in the stool. Most interestingly, serum IgE correlated with E coli counts, and in highly sensitized infants, IgE correlated with Bacteroides counts [24]. Thus, certain probiotics seem to influence the gut's allergen-stimulated inflammatory response and provide a barrier effect against antigens that might otherwise ultimately lead to systemic allergic symptoms (such as eczema).

A recent prospective study from 3 European birth cohorts found, however, no differences in gut microbiota by culture-dependent analysis of fecal samples among infants developing or not developing atopic eczema and food allergy. On the contrary, a subgroup analysis of the cohort by cultivation independent techniques indicated a significantly lower diversity in the gut microbiota of 1-week-old neonates who later manifested atopic eczema than in neonates remaining healthy during the first 18 months of life, highlighting once more that classical microbiological plating techniques are inappropriate for extensive characterization of the gut microbiota [25]. Similarly, less diverse microbial communities were found among 5-year-old allergic children than among nonallergic children by using another culture-independent technique. The same study demonstrated that Bfdbm catenulatum /pseudocatenulatum prevail in nonallergic children [26]. On the contrary, this particular Bifidobacterial species was associated with atopic eczema in a nested case-control study conducted in a different age group, country, and disease population, highlighting the complexity of the situation. As the immune modulation properties of bacteria seem to be distinctly strain specific, it cannot be ruled out that the nature of the immune response induced by a specific strain plays a more important role than its classification.

several months of life. The composition of the gut microbiota differs between healthy and allergic infants and even in countries with a high and low prevalence of allergies [21]. Mode of delivery, either vaginal or through caesarean section, also has a major impact on early colonization patterns of the infant gut [4]. In the case of allergy, the rationale for modulating the intestinal microbiota is supported by observations that allergic children have a different microbiota composition than healthy infants. The main changes associated with allergic trait are less frequent colonization with Lactobacilli and lower counts of Bifidobacteria [9,22]. In addition to these quantitative differences in the Bfdbm microbiota, qualitative differences have also been observed. Infants with AD have been found to have a more adult type Bfdbm microbiota with high prevalence of Bfdbm adolescentis. Healthy infants, on the other hand, were found to be colonized mainly by Bfdbm bifidum, typical for breast-fed infants [7,8]. The Bifidobacteria from infants with AD were found to induce a higher secretion of proinflammatory cytokines in vitro, whereas the Bifidobacteria from healthy infants induced the secretion of more antiinflammatory cytokines. Also, Bifidobacteria of dairy origin stimulated more antiinflammatory and less inflammatory cytokines than Bifidobacteria from allergic infants. In addition to differing in their induction of cytokines, Bifidobacteria from allergic and healthy infants also exhibited different in vitro adhesion to Caco-2 tissue culture cells and intestinal mucus. This difference in adhesion to the intestinal mucosa may result in a different or reduced stimulation of the immune system through the gut-associated lymphoid tissue [23]. Lower counts of Bifidobacteria have been reported in atopic vs nonatopic children preceding allergen sensitization. Bifidobacteria are hypothesized to more effectively promote tolerance to nonbacterial antigens, primarily by inhibiting the development of a Th2-type (proallergic) response. In a recent study, a positive change in stool colonization in atopic infants supplemented with Bfdbm lactis has been shown with a decrease of Bacteroides and E coli in the stool. Most interestingly, serum IgE correlated with E coli counts, and in highly sensitized infants, IgE correlated with Bacteroides counts [24]. Thus, certain probiotics seem to influence the gut's allergen-stimulated inflammatory response and provide a barrier effect against antigens that might otherwise ultimately

A recent prospective study from 3 European birth cohorts found, however, no differences in gut microbiota by culture-dependent analysis of fecal samples among infants developing or not developing atopic eczema and food allergy. On the contrary, a subgroup analysis of the cohort by cultivation independent techniques indicated a significantly lower diversity in the gut microbiota of 1-week-old neonates who later manifested atopic eczema than in neonates remaining healthy during the first 18 months of life, highlighting once more that classical microbiological plating techniques are inappropriate for extensive characterization of the gut microbiota [25]. Similarly, less diverse microbial communities were found among 5-year-old allergic children than among nonallergic children by using another culture-independent technique. The same study demonstrated that Bfdbm catenulatum /pseudocatenulatum prevail in nonallergic children [26]. On the contrary, this particular Bifidobacterial species was associated with atopic eczema in a nested case-control study conducted in a different age group, country, and disease population, highlighting the complexity of the situation. As the immune modulation properties of bacteria seem to be distinctly strain specific, it cannot be ruled out that the nature of the immune response induced by a specific strain plays a more

lead to systemic allergic symptoms (such as eczema).

important role than its classification.

Probiotic intestinal flora contributes to microbial antigen exposure in early life and is one of the most abundant sources of early immune stimulation. Because allergic immune responses manifest early in life, there has been obvious interest in the potential benefits of modifying the gastrointestinal flora by using probiotic supplementation. However, the value of probiotics for primary prevention is controversial [13,14]. So far, there have been only several studies to address the role of probiotics in primary prevention, with a reported suspicious reduction in the incidence of eczema. The role of probiotics in allergy prevention has remained controversial, and there has been an urgent call for similar studies to address this further. This chapter will try to highlight the issues with probiotics in the therapy / prevention of AD and future of this therapy. Here, firstly newly described mechanisms of probiotic effects will be defined. Later, under the light of recent literature probiotic use in AD therapy and prevention is being discussed in detail.

#### **2.1 Experimental (animal) and clinical (human) studies showing mechanisms of probiotics` effects in atopic diseases including eczema**

Although the beneficial effects of probiotics on wide variety of atopic diseases have been suggested, little is known about how probiotics modulate the immune system and atopic disease development. Currently, only limited publications are available defining the effects of probiotics in murine or human models of AD. Therefore, it is important to explore the effect of probiotics in various experimental and clinical atopic disease models.

#### **2.1.1 Maturing gut barrier: Probiotic regulation in intestinal epithelium and upregulation of host immune responses**

Recent data indicate that commensal intestinal microbiota represents a major modulator of intestinal homeostasis. Dysregulation of the symbiotic interaction between intestinal microbiota and the mucosa may result in a pathological condition with potential clinical repercussions. For instance, it is shown that mice reared in germ-free conditions have an underdeveloped immune system and have no oral tolerance. In contrast, pathogen-free mice are capable of reconstituting the bacterial flora with Bifidobacteria and tolerance development [27].

In addition to providing maturational signals for the gut-associated lymphoid tissue, probiotics balance the generation of pro- and anti-inflammatory cytokines in the gut. After probiotic consumption, decrease in fecal α-1 antitrypsin, serum TNF-α, and changes in TGFβ and other cytokines point to down-regulation of inflammatory mediators [28]. For instance, after a challenge study in infants allergic to cow's milk, fecal IgA levels were detected to be higher and TNF-α levels were lower in the Lctbs rhamnosus GG (LGG) applied group compared to the placebo [29]. Similarly, another study by Kirjavainen et al suggested that Bfdbm lactis Bb12 might modify gut microflora to alleviate early onset atopic eczema. And this modification was found to be compatible with reductions of serum TNF-α and fecal α-1-antitrypsin levels as well as an increase in fecal IgA level [23].

Moreover, probiotic bacteria may counteract the inflammatory process by stabilizing the gut microbial environment and the permeability barrier of the intestine, and by enhancing the degradation of enteral antigens and altering their immunogenicity [30]. This gut-stabilizing effect of probiotics could be explained by the improvement by probiotics of the immunological barrier of the intestine through intestinal IgA responses, specifically [31,32]. Consistent with these explanations, in children with food allergies, probiotics are shown to reverse increased intestinal permeability and to enhance frequently defective IgA responses [33].

The Role of Probiotics in Atopic Dermatitis Prevention and Therapy 359

increases in the capacity for Th1 IFN-γ responses and altered responses to skin and enteric flora. This effect was still evident 2 months after the supplementation was ceased [49]. Reduction in serum soluble CD4 as a marker of T-cell activation described by Isolauri et al. They also found significant changes in indirect markers of allergic inflammation, such as sCD4 in the serum of infants with AD supplemented with Bfdbm lactis and LGG [50]. In a randomized controlled trial by Boyle et al showed that LGG treatment during pregnancy (prenatal) for the prevention of eczema was not associated with any change in cord blood immune markers such as TGF-β, IL-10, IL-12, IL-13, IFN-γ and TNF-α as well as

Twelve human studies were included in a review and 67% showed a positive association with TGF-β1 or TGF-β2 demonstrating protection against allergy-related outcomes in infancy and early childhood. High variability in concentrations of TGF-β was noted between and within studies, some of it explained by maternal history of atopy or by consumption of probiotics. Human milk TGF-β appears to be essential in developing and maintaining appropriate immune responses in infants and may provide protection against adverse immunological outcomes, corroborating findings from experimental animal studies. In a study, aim was to evaluate the effect of probiotic supplementation on the immunological composition of breast milk and colostrum in relation to sensitization and eczema in the babies. Total IgA, secretory IgA, TGF-β1, TGF-β2, IL-10, TNF-α, and soluble CD14 were analyzed in colostrum and mature milk obtained from women treated with probiotics from gestational week 36 until delivery. The total IgA, secretory IgA, TGF-β1, TNF-α, and sCD14 in breast milk were not affected by the intake of probiotics. Supplementation of probiotics during pregnancy was associated with low levels of TGF-β2 and slightly increased levels of IL-10 in colostrum. Infants receiving breast milk with low levels of TGF-β2 were less likely to become sensitized and possibly less IgE-associated eczema in breast-fed infants during their first 2 yr of life [52]. However, another trial by Boyle et al showed that LGG treatment during pregnancy (prenatal) for the prevention of eczema was associated with decreased breast milk soluble CD14 and IgA levels, not TGF-β [51]. The difference between these studies looks probiotic species, which may

**2.1.3 Anti-inflammatory effects: Their effects on serum inflammatory parameters**  The anti-inflammatory effect of probiotics has been attributed to increased production of IL-10 by immune cells in the lamina propria, Peyer's patches and the spleen of treated animals [35-38]. Oral administration of LGG resulted in elevated IL-10 concentrations in atopic children, indicating that specific probiotics may have anti-inflammatory effects in vivo and possible enhancing regulatory or tolerance-inducing mechanisms as well. A review of the evidence from randomized controlled trials by Betsi et al about probiotics for the treatment or prevention of AD: the results of 13 relevant randomized (placebo)-controlled trials (RCTs) were reviewed: 10 of which evaluated probiotics as treatment and 3 for prevention of AD. In four of these six RCTs, clinical improvement was associated with a change in some inflammatory markers [53]. Another randomized, double-blind, placebo-controlled study conducted by Brouwer et al showed no statistically significant effects of probiotic

Some probiotics have been reported to reduce proinflammatory cytokines through Th17 cells. Suppression of this newly discovered subset of T cells by probiotics might explain effects observed in different experimental models that all involve inflammatory responses. For instance, Lctb casei suppressed inflammation reducing proinflammatory cytokines released from Th17 cells [54]. Also, in a study administration of the probiotics mixture

Dendritic and Treg cell numbers [51].

affect the immunological composition of breast milk.

supplementation on inflammatory parameters [47].

#### **2.1.2 Immunomodulation: Th1/Th2 balance, IgE production and cytokines**

In addition to maturing gut barrier, certain strains of Lactobacilli and Bifidobacteria modulate the production of cytokines by monocytes and lymphocytes, and may divert the immune system in a regulatory or tolerant mode [27,34]. Nonetheless, there are still some studies showing no significant effects of probiotics on either Th1 or Th2 cell responses to allergens. Although the cytokine stimulation profiles of different probiotic strains vary, the strains isolated from healthy infants mainly stimulate non-inflammatory cytokines [35]. Therefore, it seems that changes in cytokine profile induced by probiotics may be probiotic strain- or site-specific and dependent on the experimental system used. For instance, Lctbs reuteri induced proinflammatory and Th1 cytokines; and Bfdbm bifidum/infantis and Lctbs lactis reduced Th2 cytokines [36].

Several studies have shown the immunomodulatory effects of probiotic bacteria. In one study, Bfdbm bifidum / infantis and Lctbs lactis reduced Th2 cytokines and acted as potent inducers of IL-10 production in different peripheral blood mononuclear cell cultures [37]. In another study, eight common Lctbs strains were studied with respect to induction of cytokines by the murine gut mucosa in response to a parenterally administered antigen. Lctbs reuteri induced proinflammatory and Th1 cytokines; however, Lctbs casei tended to induce IL-10 / IL-4 [38]. Yet on the contrary, in some children receiving probiotics, reduced IL-10 responsiveness to house dust mites allergens was observed [39]. In a study, the effects of feeding Lctbs F19 were evaluated during weaning on the incidence of eczema and Th1/Th2 balance. In a double-blind, placebo-controlled randomized intervention trial, infants were fed cereals with (n:89) or without Lctbs F19 (n:90) from 4 to 13 months of age. At 13 months of age, the IFN-γ/ IL-4 mRNA ratio was significantly higher in the probiotic compared with the placebo group. The higher Th1/Th2 ratio in the probiotic compared with the placebo group suggests enhancing effects of Lctbs F19 on the T cell-mediated immune response. And probiotics also increased Th1 cytokines and inhibited allergen-induced IgE and Th2 cytokines in some atopic children [40,41].

In a mouse model, effect of oral probiotics administration, including Bfdbm lactis/bifidum and Lctbs acidophilus, on mice with ovalbumin (OVA)-induced food allergy was studied. The mice treated with probiotics suppressed production of the OVA-specific IgE, IgG1, and IgA. Additionally, the level of IL-4 was significantly lower, and the levels of INF-γ and IL-10 were significantly higher in the mice treated with probiotics than that in the nontreated mice [42]. Another murine model showed that oral administration of an immunostimulatory DNA sequence from Bfdbm longum suppressed Th2 immune responses in mice and inhibited IgE production in vitro [43]. A final study showed that the administration of either Bfdbm lactis Bb-12 or LGG suppressed antigen-specific IgE production too [44].

A decrease in the secretion of pro-inflammatory cytokines, IFN-γ, TNF-α and IL-12 has been demonstrated. Consistently, in an experimental study, probiotic supplementation decreased the severity of allergic skin responses in allergen-sensitized pigs with a corresponding increase in IFN-γ expression [45]. However, the study by Rosenfeldt et al. demonstrated no significant changes in serum cytokines (IL-2, IL-4, IL-10 and IFN-γ) during 6 weeks of probiotic treatment [46]. Another study by Brouwer et al. showed no statistically significant effects of probiotic supplementation on cytokine production (IL-4, IL-5 and IFN-γ) as well [47]. These results differ from those of Pohjavuori et al, who were able to demonstrate an increase of IFN-γ production in peripheral blood mononuclear cell in infants with AD treated with LGG instead of placebo [48]. Additionally, the improvement in AD severity of very young children with probiotic treatment was detected to be associated with significant

In addition to maturing gut barrier, certain strains of Lactobacilli and Bifidobacteria modulate the production of cytokines by monocytes and lymphocytes, and may divert the immune system in a regulatory or tolerant mode [27,34]. Nonetheless, there are still some studies showing no significant effects of probiotics on either Th1 or Th2 cell responses to allergens. Although the cytokine stimulation profiles of different probiotic strains vary, the strains isolated from healthy infants mainly stimulate non-inflammatory cytokines [35]. Therefore, it seems that changes in cytokine profile induced by probiotics may be probiotic strain- or site-specific and dependent on the experimental system used. For instance, Lctbs reuteri induced proinflammatory and Th1 cytokines; and Bfdbm bifidum/infantis and Lctbs

Several studies have shown the immunomodulatory effects of probiotic bacteria. In one study, Bfdbm bifidum / infantis and Lctbs lactis reduced Th2 cytokines and acted as potent inducers of IL-10 production in different peripheral blood mononuclear cell cultures [37]. In another study, eight common Lctbs strains were studied with respect to induction of cytokines by the murine gut mucosa in response to a parenterally administered antigen. Lctbs reuteri induced proinflammatory and Th1 cytokines; however, Lctbs casei tended to induce IL-10 / IL-4 [38]. Yet on the contrary, in some children receiving probiotics, reduced IL-10 responsiveness to house dust mites allergens was observed [39]. In a study, the effects of feeding Lctbs F19 were evaluated during weaning on the incidence of eczema and Th1/Th2 balance. In a double-blind, placebo-controlled randomized intervention trial, infants were fed cereals with (n:89) or without Lctbs F19 (n:90) from 4 to 13 months of age. At 13 months of age, the IFN-γ/ IL-4 mRNA ratio was significantly higher in the probiotic compared with the placebo group. The higher Th1/Th2 ratio in the probiotic compared with the placebo group suggests enhancing effects of Lctbs F19 on the T cell-mediated immune response. And probiotics also increased Th1 cytokines and inhibited allergen-induced IgE

In a mouse model, effect of oral probiotics administration, including Bfdbm lactis/bifidum and Lctbs acidophilus, on mice with ovalbumin (OVA)-induced food allergy was studied. The mice treated with probiotics suppressed production of the OVA-specific IgE, IgG1, and IgA. Additionally, the level of IL-4 was significantly lower, and the levels of INF-γ and IL-10 were significantly higher in the mice treated with probiotics than that in the nontreated mice [42]. Another murine model showed that oral administration of an immunostimulatory DNA sequence from Bfdbm longum suppressed Th2 immune responses in mice and inhibited IgE production in vitro [43]. A final study showed that the administration of either

A decrease in the secretion of pro-inflammatory cytokines, IFN-γ, TNF-α and IL-12 has been demonstrated. Consistently, in an experimental study, probiotic supplementation decreased the severity of allergic skin responses in allergen-sensitized pigs with a corresponding increase in IFN-γ expression [45]. However, the study by Rosenfeldt et al. demonstrated no significant changes in serum cytokines (IL-2, IL-4, IL-10 and IFN-γ) during 6 weeks of probiotic treatment [46]. Another study by Brouwer et al. showed no statistically significant effects of probiotic supplementation on cytokine production (IL-4, IL-5 and IFN-γ) as well [47]. These results differ from those of Pohjavuori et al, who were able to demonstrate an increase of IFN-γ production in peripheral blood mononuclear cell in infants with AD treated with LGG instead of placebo [48]. Additionally, the improvement in AD severity of very young children with probiotic treatment was detected to be associated with significant

Bfdbm lactis Bb-12 or LGG suppressed antigen-specific IgE production too [44].

**2.1.2 Immunomodulation: Th1/Th2 balance, IgE production and cytokines** 

lactis reduced Th2 cytokines [36].

and Th2 cytokines in some atopic children [40,41].

increases in the capacity for Th1 IFN-γ responses and altered responses to skin and enteric flora. This effect was still evident 2 months after the supplementation was ceased [49].

Reduction in serum soluble CD4 as a marker of T-cell activation described by Isolauri et al. They also found significant changes in indirect markers of allergic inflammation, such as sCD4 in the serum of infants with AD supplemented with Bfdbm lactis and LGG [50].

In a randomized controlled trial by Boyle et al showed that LGG treatment during pregnancy (prenatal) for the prevention of eczema was not associated with any change in cord blood immune markers such as TGF-β, IL-10, IL-12, IL-13, IFN-γ and TNF-α as well as Dendritic and Treg cell numbers [51].

Twelve human studies were included in a review and 67% showed a positive association with TGF-β1 or TGF-β2 demonstrating protection against allergy-related outcomes in infancy and early childhood. High variability in concentrations of TGF-β was noted between and within studies, some of it explained by maternal history of atopy or by consumption of probiotics. Human milk TGF-β appears to be essential in developing and maintaining appropriate immune responses in infants and may provide protection against adverse immunological outcomes, corroborating findings from experimental animal studies. In a study, aim was to evaluate the effect of probiotic supplementation on the immunological composition of breast milk and colostrum in relation to sensitization and eczema in the babies. Total IgA, secretory IgA, TGF-β1, TGF-β2, IL-10, TNF-α, and soluble CD14 were analyzed in colostrum and mature milk obtained from women treated with probiotics from gestational week 36 until delivery. The total IgA, secretory IgA, TGF-β1, TNF-α, and sCD14 in breast milk were not affected by the intake of probiotics. Supplementation of probiotics during pregnancy was associated with low levels of TGF-β2 and slightly increased levels of IL-10 in colostrum. Infants receiving breast milk with low levels of TGF-β2 were less likely to become sensitized and possibly less IgE-associated eczema in breast-fed infants during their first 2 yr of life [52]. However, another trial by Boyle et al showed that LGG treatment during pregnancy (prenatal) for the prevention of eczema was associated with decreased breast milk soluble CD14 and IgA levels, not TGF-β [51]. The difference between these studies looks probiotic species, which may affect the immunological composition of breast milk.

#### **2.1.3 Anti-inflammatory effects: Their effects on serum inflammatory parameters**

The anti-inflammatory effect of probiotics has been attributed to increased production of IL-10 by immune cells in the lamina propria, Peyer's patches and the spleen of treated animals [35-38]. Oral administration of LGG resulted in elevated IL-10 concentrations in atopic children, indicating that specific probiotics may have anti-inflammatory effects in vivo and possible enhancing regulatory or tolerance-inducing mechanisms as well. A review of the evidence from randomized controlled trials by Betsi et al about probiotics for the treatment or prevention of AD: the results of 13 relevant randomized (placebo)-controlled trials (RCTs) were reviewed: 10 of which evaluated probiotics as treatment and 3 for prevention of AD. In four of these six RCTs, clinical improvement was associated with a change in some inflammatory markers [53]. Another randomized, double-blind, placebo-controlled study conducted by Brouwer et al showed no statistically significant effects of probiotic supplementation on inflammatory parameters [47].

Some probiotics have been reported to reduce proinflammatory cytokines through Th17 cells. Suppression of this newly discovered subset of T cells by probiotics might explain effects observed in different experimental models that all involve inflammatory responses. For instance, Lctb casei suppressed inflammation reducing proinflammatory cytokines released from Th17 cells [54]. Also, in a study administration of the probiotics mixture

The Role of Probiotics in Atopic Dermatitis Prevention and Therapy 361

grade inflammation, practically the same as in chronic and balanced helminth infection, which is associated with activation of Treg cells suppressing allergic inflammation. Since the colonization is yet transient, the induction of Treg cells is not permanent. Thus when these immunologic effects no longer operate, the clinical effect is simultaneously lost. For instance, when helminth infections are treated, the prevalence of allergic sensitization increases rapidly.

Recent studies also provided evidence that one effect of probiotics may involve induction of differentiation of IL-10-dependent, TGF-β-bearing Tregs. In a food allergy mouse model, oral administration of Bfdbm bifidum and Lctbs acidophilus suppressed OVA-specific IgE production, which was caused by inducing Treg -associated TGF-β production [62]. Another study demonstrated that neonatal application of probiotic bacteria inhibits subsequent allergic sensitization and airway disease in a murine model of asthma by induction of Treg

Generation of CD4+/Foxp3+ Treg cells by probiotics administration suppresses immune and allergic disorders. Recently, two studies reported that oral administration of a certain probiotic strain could increase Foxp3+ Tregs [55]. It is known that the lower percentage of epidermal or dermal Foxp3+ cells in eczematous dermatitis might contribute to their pathogenesis [64]. In a recent study, a mixture of probiotics (Lctbs acidophilus, Lctbs casei, Lctbs reuteri, Bfdbm bifidium, and Streptococcus thermophilus) was identified that upregulates CD4+/Foxp3+ Treg cells. Administration of the probiotics mixture induced both T-cell and B-cell hyporesponsiveness and down-regulated Th1, Th2, and Th17 cytokines [55,65]. It also induced generation of CD4+/Foxp3+ Tregs from the CD4+/25- population and increased the suppressor activity of naturally occurring CD4+/25+ Tregs. Conversion of T cells into Foxp3+ Tregs is directly mediated by regulatory DCs that express high levels of IL-10 and TGF-β. In a murine AD model, treatment with this probiotic mixture significantly inhibited the clinical symptoms of AD progression by reducing IgE levels [total and specific IgE levels], infiltrated lymphocytes and granulocytes, and levels of AD-associated cytokines [55]. Lctbs casei treatment enhanced the frequency of FoxP3(+) Treg in the skin and increased the production of IL-10 by CD4+/25+ Treg cells in skin draining lymph nodes of hapten-sensitized mice. These data demonstrate that orally administered Lctbs casei (DN-114 001) efficiently alleviate T cell-mediated skin inflammation without causing immune suppression, via mechanisms that include control of CD8+ effector T cells and involve regulatory CD4+ T cells. Lctbs casei may thus represent a probiotic of potential interest for immunomodulation of T cell-mediated allergic skin diseases in human [66]. However, another study showed that Foxp3 mRNA expression at 6 months of age is higher in infants

This is a plausible explanation for the fading probiotic effect as well [57].

having AD, but it is not affected by giving probiotics from birth [67].

Several studies reveal that the probiotics differently modulate peripheral blood immune

Gerasimov et al conducted a study to assess the clinical efficacy and impact of Lctbs acidophilus DDS-1, Bfdbm lactis UABLA-12 with fructo-oligosaccharide on peripheral blood lymphocyte subsets in preschool children with moderate-to-severe AD. The percentage of CD4, and the percentage and absolute count of CD25 decreased, and the percentage and absolute count of CD8 increased in the probiotic group at week 8, compared with placebo (p:< 0.007). They found a significant correlation between CD4 percentage, CD25 percentage,

cells and TGF-β production [63].

**2.1.6 Lymphocyte subpopulations** 

parameters in healthy subjects and patients with AD.

(Lctbs acidophilus, Lctbs casei, Lctbs reuteri, Bfdbm bifidum, and Streptococcus thermophilus) induced both T-cell and B-cell hyporesponsiveness and down-regulated Th1, Th2, and Th17 cytokines [55].

A study by Woo et al evaluated the effect of Lctbs sakei supplementation in children with atopic eczema-dermatitis syndrome. In this study, compared with placebo, probiotic administration was associated with lower pretreatment-adjusted serum levels of chemokines such as CCL17 and CCL27, which were significantly correlated with SCORAD total score [56].

Probiotic-induced chronic low-grade inflammation characterized by elevation of CRP, IgE, IgA, and IL-10 was shown in some studies, the changes typically observed in helminth infection-associated induction of regulatory mechanisms. The association of increased CRP with a decreased risk of eczema at 2 years of age in allergy-prone children supports the view that chronic, low-grade inflammation protects from eczema. The findings emphasize the role of chronic microbial exposure as an immune modulator protecting from allergy [57].

A study by Rosenfeldt et al, 2 probiotic Lctbs strains (lyophilized Lctbs rhamnosus 19070- 2 and Lctbs reuteri DSM 122460) were given in combination for 6 weeks to 1- to 13-year-old children with AD. During active treatment, serum eosinophil cationic protein (ECP) levels significantly decreased. A combination of Lctbs rhamnosus and Lctbs reuteri was beneficial in the management of AD and the effect was more pronounced in atopic eczema patients [46]. Another study was conducted by Brouwer et al showed, during Lctbs species supplementation, a moderate but significant reduction in soluble ECP levels was found. ECP, a cytotoxic protein released from activated eosinophils, has been used to monitor disease activity in AD. Thus sECP might be a more sensitive marker in acute exacerbations of the eczema than a marker of disease activity per se [47]. Although this study by Brouwer et al revealed no statistically significant effects of probiotic supplementation on eosinophil protein X (EPX) in urine, Isolauri et al found significant changes in EPX in the urine of infants supplemented with Bfdbm lactis and LGG [15].

#### **2.1.4 Development of tolerogenic Dendritic cells**

Selected species of the Bfdbm genus were demonstrated to prime in vitro cultured neonatal Dendritic cell (DC)s to polarize T cell responses and may therefore be used as candidates in primary prevention of allergic diseases. Bfdbm bifidum was found to be most potent polarizer in vitro-cultured DCs to drive Th1-cell responses involving increased IFN-γ producing T cells concomitant with reduction of IL-4-producing T-cells [58]. In addition, T-cells stimulated by Bfdbm bifidum matured DCs as producers of more IL-10 [59]. Moreover, Lctbs rhamnosus, member of another genus of probiotic bacteria, modulates DC function to induce a novel form of T-cell hyporesponsiveness [60]. Lctbs reuteri/casei have been also shown to prime monocytederived DCs through the C-type lectin DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) to drive the development of Treg cells [61]. These Treg cells produce increased levels of IL-10 and are capable of inhibiting the proliferation of bystander T cells. This study suggests that the targeting of DC-SIGN by certain probiotic bacteria might explain their beneficial effect in the treatment of a number of inflammatory diseases, including AD.

#### **2.1.5 Immunoregulation by T regulatory (Treg) cells**

As mentioned earlier, Lctbs reuteri / casei have been also shown to prime monocyte-derived DCs through the DC-SIGN to drive the development of Treg cells [61]. And the probiotic combinations are alleged to cause a paradoxic Th2 stimulation and to induce chronic low-

(Lctbs acidophilus, Lctbs casei, Lctbs reuteri, Bfdbm bifidum, and Streptococcus thermophilus) induced both T-cell and B-cell hyporesponsiveness and down-regulated Th1,

A study by Woo et al evaluated the effect of Lctbs sakei supplementation in children with atopic eczema-dermatitis syndrome. In this study, compared with placebo, probiotic administration was associated with lower pretreatment-adjusted serum levels of chemokines such as CCL17 and CCL27, which were significantly correlated with SCORAD total score [56]. Probiotic-induced chronic low-grade inflammation characterized by elevation of CRP, IgE, IgA, and IL-10 was shown in some studies, the changes typically observed in helminth infection-associated induction of regulatory mechanisms. The association of increased CRP with a decreased risk of eczema at 2 years of age in allergy-prone children supports the view that chronic, low-grade inflammation protects from eczema. The findings emphasize the role

of chronic microbial exposure as an immune modulator protecting from allergy [57].

infants supplemented with Bfdbm lactis and LGG [15].

**2.1.5 Immunoregulation by T regulatory (Treg) cells** 

**2.1.4 Development of tolerogenic Dendritic cells** 

A study by Rosenfeldt et al, 2 probiotic Lctbs strains (lyophilized Lctbs rhamnosus 19070- 2 and Lctbs reuteri DSM 122460) were given in combination for 6 weeks to 1- to 13-year-old children with AD. During active treatment, serum eosinophil cationic protein (ECP) levels significantly decreased. A combination of Lctbs rhamnosus and Lctbs reuteri was beneficial in the management of AD and the effect was more pronounced in atopic eczema patients [46]. Another study was conducted by Brouwer et al showed, during Lctbs species supplementation, a moderate but significant reduction in soluble ECP levels was found. ECP, a cytotoxic protein released from activated eosinophils, has been used to monitor disease activity in AD. Thus sECP might be a more sensitive marker in acute exacerbations of the eczema than a marker of disease activity per se [47]. Although this study by Brouwer et al revealed no statistically significant effects of probiotic supplementation on eosinophil protein X (EPX) in urine, Isolauri et al found significant changes in EPX in the urine of

Selected species of the Bfdbm genus were demonstrated to prime in vitro cultured neonatal Dendritic cell (DC)s to polarize T cell responses and may therefore be used as candidates in primary prevention of allergic diseases. Bfdbm bifidum was found to be most potent polarizer in vitro-cultured DCs to drive Th1-cell responses involving increased IFN-γ producing T cells concomitant with reduction of IL-4-producing T-cells [58]. In addition, T-cells stimulated by Bfdbm bifidum matured DCs as producers of more IL-10 [59]. Moreover, Lctbs rhamnosus, member of another genus of probiotic bacteria, modulates DC function to induce a novel form of T-cell hyporesponsiveness [60]. Lctbs reuteri/casei have been also shown to prime monocytederived DCs through the C-type lectin DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) to drive the development of Treg cells [61]. These Treg cells produce increased levels of IL-10 and are capable of inhibiting the proliferation of bystander T cells. This study suggests that the targeting of DC-SIGN by certain probiotic bacteria might explain their

beneficial effect in the treatment of a number of inflammatory diseases, including AD.

As mentioned earlier, Lctbs reuteri / casei have been also shown to prime monocyte-derived DCs through the DC-SIGN to drive the development of Treg cells [61]. And the probiotic combinations are alleged to cause a paradoxic Th2 stimulation and to induce chronic low-

Th2, and Th17 cytokines [55].

grade inflammation, practically the same as in chronic and balanced helminth infection, which is associated with activation of Treg cells suppressing allergic inflammation. Since the colonization is yet transient, the induction of Treg cells is not permanent. Thus when these immunologic effects no longer operate, the clinical effect is simultaneously lost. For instance, when helminth infections are treated, the prevalence of allergic sensitization increases rapidly. This is a plausible explanation for the fading probiotic effect as well [57].

Recent studies also provided evidence that one effect of probiotics may involve induction of differentiation of IL-10-dependent, TGF-β-bearing Tregs. In a food allergy mouse model, oral administration of Bfdbm bifidum and Lctbs acidophilus suppressed OVA-specific IgE production, which was caused by inducing Treg -associated TGF-β production [62]. Another study demonstrated that neonatal application of probiotic bacteria inhibits subsequent allergic sensitization and airway disease in a murine model of asthma by induction of Treg cells and TGF-β production [63].

Generation of CD4+/Foxp3+ Treg cells by probiotics administration suppresses immune and allergic disorders. Recently, two studies reported that oral administration of a certain probiotic strain could increase Foxp3+ Tregs [55]. It is known that the lower percentage of epidermal or dermal Foxp3+ cells in eczematous dermatitis might contribute to their pathogenesis [64]. In a recent study, a mixture of probiotics (Lctbs acidophilus, Lctbs casei, Lctbs reuteri, Bfdbm bifidium, and Streptococcus thermophilus) was identified that upregulates CD4+/Foxp3+ Treg cells. Administration of the probiotics mixture induced both T-cell and B-cell hyporesponsiveness and down-regulated Th1, Th2, and Th17 cytokines [55,65]. It also induced generation of CD4+/Foxp3+ Tregs from the CD4+/25- population and increased the suppressor activity of naturally occurring CD4+/25+ Tregs. Conversion of T cells into Foxp3+ Tregs is directly mediated by regulatory DCs that express high levels of IL-10 and TGF-β. In a murine AD model, treatment with this probiotic mixture significantly inhibited the clinical symptoms of AD progression by reducing IgE levels [total and specific IgE levels], infiltrated lymphocytes and granulocytes, and levels of AD-associated cytokines [55]. Lctbs casei treatment enhanced the frequency of FoxP3(+) Treg in the skin and increased the production of IL-10 by CD4+/25+ Treg cells in skin draining lymph nodes of hapten-sensitized mice. These data demonstrate that orally administered Lctbs casei (DN-114 001) efficiently alleviate T cell-mediated skin inflammation without causing immune suppression, via mechanisms that include control of CD8+ effector T cells and involve regulatory CD4+ T cells. Lctbs casei may thus represent a probiotic of potential interest for immunomodulation of T cell-mediated allergic skin diseases in human [66]. However, another study showed that Foxp3 mRNA expression at 6 months of age is higher in infants having AD, but it is not affected by giving probiotics from birth [67].

#### **2.1.6 Lymphocyte subpopulations**

Several studies reveal that the probiotics differently modulate peripheral blood immune parameters in healthy subjects and patients with AD.

Gerasimov et al conducted a study to assess the clinical efficacy and impact of Lctbs acidophilus DDS-1, Bfdbm lactis UABLA-12 with fructo-oligosaccharide on peripheral blood lymphocyte subsets in preschool children with moderate-to-severe AD. The percentage of CD4, and the percentage and absolute count of CD25 decreased, and the percentage and absolute count of CD8 increased in the probiotic group at week 8, compared with placebo (p:< 0.007). They found a significant correlation between CD4 percentage, CD25 percentage,

The Role of Probiotics in Atopic Dermatitis Prevention and Therapy 363

Sudo et al 27 Bfdbm Oral tolerance ↑

15,29,50,76 LGG Fecal IgA levels <sup>↑</sup>

Malin et al 31 LGG Gut defense ↑ Kaila et al 33 Lctbs Intestinal permeability ↓

Maassen et al 38,105 Lctbs casei IL-10 Production ↑ Maassen et al 38,105 Lctbs reuteri Th1 Cytokines ↑ Maassen et al 38,105 Lctbs casei IL-4 Production ↑

Takahashi 43 Bfdbm longum Th2 Cytokines ↓ Takahashi 43 Bfdbm longum IgE Production ↓

Kruisselbrink et al 39 Lctbs plantarum IL-10 Production ↓ Hart et al 59 Bfdbm bifidum IL-10 Production ↑

Niers et al 58 Bfdbm bifidum Most potent Dendritic cell

Hart et al 59 Bfdbm bifidum Human Dendritic cell

Braat et al 60 Lctbs rhamnosus Dendritic cell function

Smits et al 61 Lctbs reuteri / casei Prime monocyte-derived

Lctbs rhamnosus GG

Niers et al 37,58,82 Bfdbm bifidum /

Niers et al 37,58,82 Bfdbm bifidum /

Kim et al 42,62,83 Bfdbm lactis/ bifidum;

Kim et al 42,62,83 Bfdbm lactis/ bifidum;

Kim et al 42,62,83 Bfdbm lactis/ bifidum;

Kim et al 42,62,83 Bfdbm lactis/ bifidum;

Sistek et al 41 Lctbs rhamnosus GG

Isolauri et al

Isolauri et al 15,29,50,76

**References Probiotic Strain Effect of probiotic Outcome** 

**Maturing Gut Barrier**

**Immunomodulation** 

(LGG) Gut-stabilizing effect <sup>↑</sup>

infantis; Lctbs lactis Th2 Cytokines <sup>↓</sup>

infantis; Lctbs lactis IL-10 Production <sup>↑</sup>

Lctbs acidophilus IL-10 Production <sup>↑</sup>

Lctbs acidophilus IL-4 Production <sup>↓</sup>

Lctbs acidophilus IFN-γ Production <sup>↑</sup>

Lctbs acidophilus IgE Production <sup>↓</sup>

(LGG) IL-10 Production <sup>↑</sup>

**Th1/Th2 balance** 

Serum Inflammatory

Parameters

polarizer in vitro <sup>↑</sup>

phenotype modulator <sup>↑</sup>

modulator <sup>↑</sup>

Dendritic cell <sup>↑</sup>

CD25 absolute count, and SCORAD values in the probiotic group at week 8. The administration of a probiotic mixture and fructo-oligosaccharide was correlated with significant clinical improvement in children with AD, with corresponding lymphocyte subpopulation changes in peripheral blood [68].

However, in another study major lymphocyte subsets were not affected by the probiotic intervention. The expression of CD4+/25+ T cells was similar in healthy subjects and AD patients, whereas CD4+/54+ decreased significantly in patients with AD and remained uninfluenced in healthy subjects. The purpose of a study by Roessler et al was to elucidate the influence of a probiotic drink containing a combination of the probiotics Lctbs paracasei Lpc-37, Lctbs acidophilus 74-2 and Bfdbm animalis subsp. lactis DGCC 420 (Bfdbm lactis 420) in healthy volunteers and in patients with AD on clinical and immunological parameters and their detection in feces. In a double-blind, randomized cross-over study was conducted in 15 healthy adults and 15 patients with AD. The probiotic product or placebo was given over 2 months. In AD patients, the SCORAD tended to decrease by 15.5% (P:0.08). However, CD57+ increased significantly in healthy subjects after probiotic intake and was not changed in patients [69].

#### **2.1.7 Toll-like receptor (TLR) stimulation**

A number of experiments indicate that infectious agents can promote protection from ADs through mechanisms independent of their constitutive antigens, leading to stimulation of non-antigen specific receptors such as TLRs. A family of pattern recognition receptors such as TLRs on gut lymphoid and epithelial cells mediates innate immune responses to bacterial molecular patterns and, thereby, orchestrates acquired immunity. The transient protection offered by probiotics against IgE-associated allergic diseases is based on stimulation of TLRs, which produce mediators such as IL-6; these further induce IgA differentiation from naive B cells. Both these events were shown to to occur after probiotic administration to infants with eczema, as well as in infants who showed increased levels of serum CRP, IL-10, and IgE at age 6 months.

Similarly, TLR stimulation was also thought to happen after probiotic administration in infants with eczema who showed increased levels of serum CRP, IL-10, and IgE [57]. This probiotic-induced low-grade inflammation was characterized by elevation of CRP, IgE, IgA, and IL-10, the changes typically observed in helminth infection-associated induction of regulatory mechanisms. Moreover, the association of increased CRP with a decreased risk of eczema at 2 years of age in allergy-prone children supports the view that chronic, low-grade inflammation protects from eczema. The findings emphasize the role of chronic microbial exposure as an immune modulator protecting from allergy thru activation of Treg cells. Consistently, lactic acid bacteria species such as Bfdbm bifidum / infantis and Lctbs salivarius were shown to be capable of activating TLR-2 [70]. Oral administration of Lctbs reuteri attenuated major characteristics of an asthmatic response, including airway eosinophilia, local cytokine responses, and hyperresponsiveness to methacholine. This effect of Lctbs reuteri on the allergic airway response was found to be dependent on TLR-9 [71].

In summary, local influences of probiotics potentially include reduction of gut permeability and systemic penetration of antigens, increased local IgA production, and alteration of local inflammation or tolerance induction. Some possible systemic effects consist of antiinflammatory effects mediated by TLRs, Th1 skewing of responses to allergens, and activation of tolerogenic DCs, in addition to Treg cell production. [The various effects of different probiotic strains in atopic diseases as well as in AD are summarized in table 1].

CD25 absolute count, and SCORAD values in the probiotic group at week 8. The administration of a probiotic mixture and fructo-oligosaccharide was correlated with significant clinical improvement in children with AD, with corresponding lymphocyte

However, in another study major lymphocyte subsets were not affected by the probiotic intervention. The expression of CD4+/25+ T cells was similar in healthy subjects and AD patients, whereas CD4+/54+ decreased significantly in patients with AD and remained uninfluenced in healthy subjects. The purpose of a study by Roessler et al was to elucidate the influence of a probiotic drink containing a combination of the probiotics Lctbs paracasei Lpc-37, Lctbs acidophilus 74-2 and Bfdbm animalis subsp. lactis DGCC 420 (Bfdbm lactis 420) in healthy volunteers and in patients with AD on clinical and immunological parameters and their detection in feces. In a double-blind, randomized cross-over study was conducted in 15 healthy adults and 15 patients with AD. The probiotic product or placebo was given over 2 months. In AD patients, the SCORAD tended to decrease by 15.5% (P:0.08). However, CD57+ increased significantly in healthy subjects after probiotic intake and was

A number of experiments indicate that infectious agents can promote protection from ADs through mechanisms independent of their constitutive antigens, leading to stimulation of non-antigen specific receptors such as TLRs. A family of pattern recognition receptors such as TLRs on gut lymphoid and epithelial cells mediates innate immune responses to bacterial molecular patterns and, thereby, orchestrates acquired immunity. The transient protection offered by probiotics against IgE-associated allergic diseases is based on stimulation of TLRs, which produce mediators such as IL-6; these further induce IgA differentiation from naive B cells. Both these events were shown to to occur after probiotic administration to infants with eczema, as well as in infants who showed increased levels of serum CRP, IL-10,

Similarly, TLR stimulation was also thought to happen after probiotic administration in infants with eczema who showed increased levels of serum CRP, IL-10, and IgE [57]. This probiotic-induced low-grade inflammation was characterized by elevation of CRP, IgE, IgA, and IL-10, the changes typically observed in helminth infection-associated induction of regulatory mechanisms. Moreover, the association of increased CRP with a decreased risk of eczema at 2 years of age in allergy-prone children supports the view that chronic, low-grade inflammation protects from eczema. The findings emphasize the role of chronic microbial exposure as an immune modulator protecting from allergy thru activation of Treg cells. Consistently, lactic acid bacteria species such as Bfdbm bifidum / infantis and Lctbs salivarius were shown to be capable of activating TLR-2 [70]. Oral administration of Lctbs reuteri attenuated major characteristics of an asthmatic response, including airway eosinophilia, local cytokine responses, and hyperresponsiveness to methacholine. This effect of Lctbs reuteri on the allergic airway response was found to be dependent on TLR-9 [71]. In summary, local influences of probiotics potentially include reduction of gut permeability and systemic penetration of antigens, increased local IgA production, and alteration of local inflammation or tolerance induction. Some possible systemic effects consist of antiinflammatory effects mediated by TLRs, Th1 skewing of responses to allergens, and activation of tolerogenic DCs, in addition to Treg cell production. [The various effects of different probiotic strains in atopic diseases as well as in AD are summarized in table 1].

subpopulation changes in peripheral blood [68].

not changed in patients [69].

and IgE at age 6 months.

**2.1.7 Toll-like receptor (TLR) stimulation** 


The Role of Probiotics in Atopic Dermatitis Prevention and Therapy 365

**Atopic (IgE-associated)** 

Viljanen et al 28,72 LGG Atopic eczema/dermatitis

Sistek et al 41 Lctbs rhamnosus + Bfdbm lactis

Rosenfeldt et al 49 Lctbs rhamnosus + Lctbs

Wickens et al 81 Lctbs rhamnosus, Bfdbm

Niers et al 37,58,82 Bfdbm bifidum, Bfdbm

Kim et al 42,62,83 Bfdbm bifidum, Bfdbm

Dotterud et al 84 LGG, Lctbs acidophilus,

Gerasimov et al 68 Lctbs acidophilus, Bfdbm

Kuitunen et al 74 Lctbs+ Bfdbm+

15,29,50,76 Bfdbm or Lctbs Food (cow's milk) Allergy <sup>↓</sup> Wickens et al 81 Lctbs rhamnosus IgE-associated eczema ↓

Majamaa et al 15 LGG Food-sensitized eczema ↓

Abrahamsson et al 75 Lctbs reuteri ATCC 55730 Atopic eczema ↓

Kalliomäki et al 16 LGG Atopic dermatitis ↓ Woo et al 56 Lctbs sakei Atopic dermatitis ↓ Weston et al 78 Lctbs fermentum Atopic dermatitis ↓ Hoang et al 79 Lctbs rhamnosus Atopic dermatitis ↓ Hattori et al 80 Bfdbm breve Atopic dermatitis ↓

Mix (LGG, Lctbs rhamnosus LC705, Bfdbm breve, Propionibacterium)

Mix (LGG, Lctbs rhamnosus LC705, Bfdbm breve, Propionibacterium)

Böttcher et al 52 Lctbs reuteri Atopic dermatitis

et al 85 Escherichia coli Atopic dermatitis (IgE

West et al 40 Lctbs casei F19 Atopic dermatitis ↓

Isolauri et al

Kukkonen et al 73,

Marschan et al 57

Lodinova-Zadnikova

108

**References Probiotic Species Type of Atopic Dermattis Outcome** 

**Eczema**

Eczema , food-sensitized atopy <sup>↓</sup>

Propionibacteria IgE-associated allergy <sup>↓</sup>

reuteri Atopic eczema <sup>↓</sup>

animalis (Bb–12) Atopic dermatitis <sup>↓</sup>

lactis, Lactococcus lactis Atopic dermatitis <sup>↓</sup>

lactis, Lctbs acidophilus Atopic dermatitis <sup>↓</sup>

Bfdbm animalis (Bb–12) Atopic dermatitis <sup>↓</sup>

lactis Atopic dermatitis <sup>↓</sup>

syndrome <sup>↓</sup>

Atopic eczema ↓

Atopic dermatitis ↓

(sensitization) <sup>↓</sup>

allergies) <sup>↓</sup>

**Non-atopic Eczema**


**Abbreviations**: Lctbs = Lactobacillus; Bfdbm = Bifidobacterium; LGG= Lactobacillus rhamnosus GG; ↑= increase in symptoms or negative effect; ↓= decrease in symptoms or positive effect; ↔ = No change in symptoms or no effect

Table 1. Various mechanisms for effects of probiotic strains in atopic disorders including eczema are shown from experimental (animal) and clinical (human) studies referred in the chapter text.
