**2.1 Etiology of NTM infections**

NTM are environmental organisms found in not only in natural and tap water, but also in soil, dust, plants, animals, and food (Falkinham, 1996, 2002; Jarzebowski & Young, 2005; Sugita et al., 2000; Tortoli, 2006). Presently, NTM consist of more than 130 species, with approximately 60 of these being suspected or known to cause disease. However, NTM infections are not transmitted between humans or between animals and humans (Cook, 2010). NTM infection can result in skin and pulmonary disease, lymphadenitis, gastrointestinal disease, and in severely immunocompromised individuals, disseminated disease (McGrath, 2010). Moreover, the progression of NTM infection to clinical disease requires one or more predisposing host conditions; NTM-PD typically occurs in patients who are not obviously immunosuppressed, but who nearly always have pre-existing abnormalities.

Notably, approximately 80% of patients with NTM disease are middle-aged or elderly women (Cook, 2010), and it is suspected that the high rate of NTM lung disease in postmenopausal women is due to their lower estrogen levels (Koh & Kwon, 2005). Other hypotheses for the higher disease rate in women include differences in the anatomy and physiology of the respiratory tract, combined with repeated infections by different strains over time (Chalermskulrat et al., 2002). Most female patients have underlying bronchiectasis that typically requires computed tomography (CT) examination for detection and that is associated with previous histories of lung infection or other, often obscure, underlying causes.

Chronic pulmonary manifestations of NTM infections, which are among the most common in NTM-PD patients, include chronic obstructive pulmonary disease (COPD), bronchiectasis, periostitis, *Mycobacterium tuberculosis* (TB) infection, cystic fibrosis, and pneumoconiosis. Patients receiving treatment with TNF-α blockers, or those with certain body characteristics (*e.g.*, pectus excavatum or scoliosis, particularly in postmenopausal women) are at higher risk for such manifestations, although NTM infection in individuals without risk factors is well reported (Griffith et al., 2007). Impairment of local immune function, including clearance of secretions, abnormal composition of airway surface liquid, and airway and mucosal damage due to chronic PD**,** may increase the propensity for NTM-PD (Morrissey, 2007). In addition, although a clear association exists between bronchiectasis and NTM disease (Cook, 2010), NTM infection also develops prior to the manifestation of bronchiectasis (Holling et al., 2002; Kubo et al., 1998; Moore, 1993; Primak et al., 1995). Thus, the observations in bronchiectasis patients suggest that bronchiectasis appears to be both a risk factor and a consequence of NTM infection (Barker, 2002).

#### **2.2 Types of NTM-PD**

Chest radiographs are not as sensitive as HRCT scanning for detecting abnormalities associated with NTM-PD (Kubo et al., 1998; Olivier, 1998; Swensen et al., 1994; Tanaka et al., 2001; Winttram & Weisbrad, 2002). CT can further characterize cavities and reveal associated bronchiectasis and pleural thickening (Ellisi & Hansell, 2002; Hartman et al., 1993). Three prototypical presentations of lung disease are reported in NTM-PD: (1) cavitary disease, (2) fibronodular bronchiectasis, and (3) hypersensitivity pneumonitis (HP) (Field & Cowie, 2006). The two former types are the most common manifestations observed in NTM-PD patients (Goo & Im, 2002).

#### 1. Cavitary disease

246 Rheumatoid Arthritis – Etiology, Consequences and Co-Morbidities

NTM are environmental organisms found in not only in natural and tap water, but also in soil, dust, plants, animals, and food (Falkinham, 1996, 2002; Jarzebowski & Young, 2005; Sugita et al., 2000; Tortoli, 2006). Presently, NTM consist of more than 130 species, with approximately 60 of these being suspected or known to cause disease. However, NTM infections are not transmitted between humans or between animals and humans (Cook, 2010). NTM infection can result in skin and pulmonary disease, lymphadenitis, gastrointestinal disease, and in severely immunocompromised individuals, disseminated disease (McGrath, 2010). Moreover, the progression of NTM infection to clinical disease requires one or more predisposing host conditions; NTM-PD typically occurs in patients who are not obviously immunosuppressed, but who nearly always have pre-existing

Notably, approximately 80% of patients with NTM disease are middle-aged or elderly women (Cook, 2010), and it is suspected that the high rate of NTM lung disease in postmenopausal women is due to their lower estrogen levels (Koh & Kwon, 2005). Other hypotheses for the higher disease rate in women include differences in the anatomy and physiology of the respiratory tract, combined with repeated infections by different strains over time (Chalermskulrat et al., 2002). Most female patients have underlying bronchiectasis that typically requires computed tomography (CT) examination for detection and that is associated with previous histories of lung infection or other, often obscure, underlying

Chronic pulmonary manifestations of NTM infections, which are among the most common in NTM-PD patients, include chronic obstructive pulmonary disease (COPD), bronchiectasis, periostitis, *Mycobacterium tuberculosis* (TB) infection, cystic fibrosis, and pneumoconiosis. Patients receiving treatment with TNF-α blockers, or those with certain body characteristics (*e.g.*, pectus excavatum or scoliosis, particularly in postmenopausal women) are at higher risk for such manifestations, although NTM infection in individuals without risk factors is well reported (Griffith et al., 2007). Impairment of local immune function, including clearance of secretions, abnormal composition of airway surface liquid, and airway and mucosal damage due to chronic PD**,** may increase the propensity for NTM-PD (Morrissey, 2007). In addition, although a clear association exists between bronchiectasis and NTM disease (Cook, 2010), NTM infection also develops prior to the manifestation of bronchiectasis (Holling et al., 2002; Kubo et al., 1998; Moore, 1993; Primak et al., 1995). Thus, the observations in bronchiectasis patients suggest that bronchiectasis appears to be both a

Chest radiographs are not as sensitive as HRCT scanning for detecting abnormalities associated with NTM-PD (Kubo et al., 1998; Olivier, 1998; Swensen et al., 1994; Tanaka et al., 2001; Winttram & Weisbrad, 2002). CT can further characterize cavities and reveal associated bronchiectasis and pleural thickening (Ellisi & Hansell, 2002; Hartman et al., 1993). Three prototypical presentations of lung disease are reported in NTM-PD: (1) cavitary disease, (2) fibronodular bronchiectasis, and (3) hypersensitivity pneumonitis (HP) (Field & Cowie, 2006). The two former types are the most common manifestations observed in NTM-

risk factor and a consequence of NTM infection (Barker, 2002).

**2. NTM infections** 

abnormalities.

causes.

**2.2 Types of NTM-PD** 

PD patients (Goo & Im, 2002).

**2.1 Etiology of NTM infections**

This type of lung disease, which represents "a TB-like pattern" of disease, is quite similar to that associated with post-primary TB. Cavitary disease is often seen in older men with substantial smoking histories and chronic PD (*e.g.*, COPD, pneumoconiosis, prior TB, and sarcoidosis) (Bandoh et al., 2004; Christensen et al., 1981; Dhillon & Watanakunakorn, 2000; Fowler et al., 2006; Glassroth, 2008; Morita et al., 2005; Sonnenberg et al., 2000; Teosk & Lo, 1992; Wickremasinghe et al., 2005; Witly et al., 1994). Cavitary disease associated with NTM mostly occurs in the apical and posterior segments of the upper lobe, although multiple lung segments may be involved. Cavitations typically include thick walls and no air-fluid level, and are often associated with pleural thickening, which is more extensive than that seen in TB. However, pleural effusion and substantial lymph node enlargement are less common than in TB (Albelda et al., 1985; Christensen et al., 1981; Reich & Johnson, 1991; Woodring et al., 1987) (Fig. 1). The symptoms of NTM-induced cavitary disease include cough, fever, weight loss, weakness, haemoptysis, and respiratory insufficiency (Griffith et al., 2007; Piersimoni & Scarparo, 2008).

Fig. 1. HRCT images of the lungs of a 63-year-old woman with MAC-PD. *M*. *avium* was detected in several sputum cultures. (a) Cavities with thick walls and no air-fluid level were seen in the right upper lobe (arrowheads) (b) Bronchiectasis with infiltration in the right middle lobe (arrows) and a cavity in the right lower lobe (arrowhead) were detected.

#### 2. Fibronodular bronchiectasis

In fibronodular bronchiectasis, CT findings are characterized by small centrilobular nodules or tree-in-bud opacities, with cylindrical bronchiectasis typically detected in the same lobe (Han et al., 2003; Hartman et al., 2003; Moore, 1993; Obayashi et al., 1999; Primack et al., 1995; Swensen et al., 1994) (Fig. 2). Bronchiectasis is more commonly associated with NTM than in TB (Primack et al., 1995), with bilateral bronchiectasis and bronchiolitis occurring in one third of NTM patients, as detected by HRCT. However, the coexistence of bronchiectasis and bronchiolitis (*i.e.*, centrilobular nodules and mosaic pattern) is also highly suggestive of NTM infection (Koh et al., 2005). Typical HRCT findings are often observed in the right middle lobe or lingual, which are anatomically predisposed to impaired clearance of secretions, a condition referred to as "Lady Windermere syndrome" (Reich & Johnson, 1992). Fibronodular bronchiectasis is most common in elderly women without preexisting pulmonary conditions or histories of tobacco abuse, but who often have anatomic abnormalities of the chest (Chan et al., 2007; Daley & Griffith, 2002; Dhillon & Watanakunakorn, 2000; Field & Cowie, 2006; Iseman et al., 1991; Jarzembowski & Young, 2008; Okumura et al., 2008; Prince et al., 1989; Taiwo & Glassroth, 2010). The major symptom

Nontuberculous Mycobacterium Infections in Rheumatoid Arthritis Patients 249

separate expectorated sputum samples, (2) positive culture result from at least one bronchial wash or lavage, or (3) transbronchial or other lung biopsy with mycobacterial histopathologic features (granulomatous inflammation or AFB) and positive culture for NTM, or biopsy showing mycobacterial histopathologic features and one or more sputum or bronchial

NTM patients with multiple positive cultures for the identical NTM pathogen and cavitary PD or major areas of bronchiectasis usually require therapy (Cook, 2010). Treatment of NTM infection should include at least three effective drugs, such as macrolides, for a minimum of 12 months after sputum samples appear similar to negative controls. However, long-term treatment with macrolides can lead to resistance, which is most frequently due to 23S rRNA gene mutations at positions 2058-2059. It was reported that 76% of patients receiving macrolide monotherapy or macrolide plus a fluoroquinolone developed resistance, whereas resistance only developed in 4% of patients treated with a regimen of clarithromycin, etambutol, and a rifamycin (Griffith et al., 2006). Due to the long duration of treatment, side effects, and the impact of these factors on patient compliance, the treatment outcomes of

*Mycobacterium avium* complex (MAC) is the term used to describe a group of slow-growing, nonpigmented (although a yellow pigment may be produced in the absence of light) AFB (Griffith et al., 2007; Inderljed et al., 1993; Tortoli, 2006). MAC species are found worldwide, but are isolated more frequently in temperate regions, including the USA, Europe, Japan, and South Africa (Inderljed et al., 1993). MAC consists of at least two major mycobacterial species, *M. avium* and *M. intracellulare*, which cannot be differentiated on the basis of traditional physical and biochemical tests, and require specific DNA probes for identification. MAC is the most common cause of NTM infections and predominantly results in pulmonary or disseminated disease (Haverkort, 2003; Marin-Casabona et al., 2004; Thomsen et al., 2002). *M. avium* is the more important pathogen in disseminated disease,

MAC-PD is predominantly observed in postmenopausal, non-smoking, Caucasian females (Griffith et al., 2007). In Japan, among 273 newly diagnosed MAC-PD cases between 1996 and 2002, 70.3% were female with a mean age of 63.2 years (Okumura et al., 2008). The HRCT findings of MAC-PD also exhibit all three forms of lung disease, as described for NTM-PD, namely cavitary disease, fibronodular bronchiectasis, and HP (Cappelluti et al., 2003; Embil et al., 1997; Glassroth, 2008; Kahana et al., 1997). Fibronoduar bronchiectasis caused by MAC is most frequently observed in women >60 years old, and compared to patients with other types of NTM infection, the lingual and right middle lobe tend to be more severely and progressively involved (Hollings et al., 2002; Kim et al., 2005; Kubo et al., 1998; Obayashi et al., 1999; Prince et al., 1989; Tanaka et al., 2001). In a recent clinical study, MAC was cultured from the sputum of 25% of the patients with fibronodular bronchiectasis, and MAC infection was documented in 50% of bronchoscopies, including BAL and transbronchial biopsies (Griffith et al., 2007). Although the cornerstones of MAC treatment are the macrolides clarithromycin, azithromycin, and ethambutol, MAC species are saprophytic and possess cell walls that are relatively impenetrable to an array of chemicals,

endowing them with intrinsic resistance to many antimicrobials (Mdluli et al., 1998).

NTM are variable and often poor (Glassroth, 2008; Piersimoni & Scarparo, 2008).

whereas *M. intracellulare* is the more common respiratory pathogen.

washings that are culture positive (Griffith et al., 2007).

**2.4 Mycobacterium avium complex** 

of fibronodular bronchiectasis is a persistent cough, and the disease can result in severe lung damage, although many patients experience a less aggressive, chronic course (Prince et al., 1989; Taiwo & Glassroth, 2010).

Fig. 2. HRCT images of the lungs of a 69-year-old woman with MAC-PD. Multiple diffuse, small, centrinodular nodules and tree-in bud opacities were seen in the all lobes.

#### 3. Hypersensitive pneumonitis

The third presentation of lung disease in NTM-PD is HP, which has first recognized as having a presentation similar to hypersensitivity lung disease (Griffith et al., 2007). HP can occur after the use of hot tubs and medicinal baths (Khoor et al., 2001). The lung inflammation and infection associated with HP are thought to lead to unique pathological features that differ distinctly from those of other NTM lung diseases. It is unclear whether MAC antigens are solely responsible for triggering host responses or whether there are other hot-tub associated cofactors (organic or inorganic) or host predispositions that may be contributing to the disease process (Griffith et al., 2007).

#### **2.3 Diagnosis and treatment of NTM**

As NTM are ubiquitous environmental saprophytes often found in water supplies, it is difficult to determine whether the growth of NTM isolates from a patient specimen represents true disease and transient colonization of a nonsterile site, such as the lung, or is a result of laboratory contamination. Pseudo-outbreaks of NTM have been described as a result of contamination of hospital laboratories, water supplies, and instruments such as bronchoscopes (Gubler et al., 1992). Once the diagnosis of NTM infection has been made, a treatment of long duration of is typically required (Stout, 2006). As the risk of contamination of the sputum by environmental mycobacteria is high, the misattribution of the clinical significance of a positive detection would lead to a useless treatment for the patient (Tortoli, 2008).

The ATS/IDSA guidelines of 2007 set criteria for the diagnosis of NTM and recommend that the minimum evaluation of a patient suspected of having NTM-PD should include the following: (1) chest radiograph or, in the absence of cavitations, chest HRCT scan, (2) collection of three or more sputum specimens for acid-fast bacterium (AFB) analysis, and (3) exclusion of other disorders such as TB and lung malignancy. Furthermore, diagnosis of NTM pulmonary infection requires the fulfillment of both clinical and microbiological criteria. Clinically, it necessary that both of the following criteria are met: (1) pulmonary symptoms, nodular or cavity opacities on chest radiograph, or a HRCT scan showing multifocal bronchiectasis with multiple small nodules, and (2) appropriate exclusion of other diagnoses. Microbiologically, only one of the following criteria are required: (1) positive culture result from at least two separate expectorated sputum samples, (2) positive culture result from at least one bronchial wash or lavage, or (3) transbronchial or other lung biopsy with mycobacterial histopathologic features (granulomatous inflammation or AFB) and positive culture for NTM, or biopsy showing mycobacterial histopathologic features and one or more sputum or bronchial washings that are culture positive (Griffith et al., 2007).

NTM patients with multiple positive cultures for the identical NTM pathogen and cavitary PD or major areas of bronchiectasis usually require therapy (Cook, 2010). Treatment of NTM infection should include at least three effective drugs, such as macrolides, for a minimum of 12 months after sputum samples appear similar to negative controls. However, long-term treatment with macrolides can lead to resistance, which is most frequently due to 23S rRNA gene mutations at positions 2058-2059. It was reported that 76% of patients receiving macrolide monotherapy or macrolide plus a fluoroquinolone developed resistance, whereas resistance only developed in 4% of patients treated with a regimen of clarithromycin, etambutol, and a rifamycin (Griffith et al., 2006). Due to the long duration of treatment, side effects, and the impact of these factors on patient compliance, the treatment outcomes of NTM are variable and often poor (Glassroth, 2008; Piersimoni & Scarparo, 2008).

#### **2.4 Mycobacterium avium complex**

248 Rheumatoid Arthritis – Etiology, Consequences and Co-Morbidities

of fibronodular bronchiectasis is a persistent cough, and the disease can result in severe lung damage, although many patients experience a less aggressive, chronic course (Prince et al.,

 Fig. 2. HRCT images of the lungs of a 69-year-old woman with MAC-PD. Multiple diffuse,

The third presentation of lung disease in NTM-PD is HP, which has first recognized as having a presentation similar to hypersensitivity lung disease (Griffith et al., 2007). HP can occur after the use of hot tubs and medicinal baths (Khoor et al., 2001). The lung inflammation and infection associated with HP are thought to lead to unique pathological features that differ distinctly from those of other NTM lung diseases. It is unclear whether MAC antigens are solely responsible for triggering host responses or whether there are other hot-tub associated cofactors (organic or inorganic) or host predispositions that may be

As NTM are ubiquitous environmental saprophytes often found in water supplies, it is difficult to determine whether the growth of NTM isolates from a patient specimen represents true disease and transient colonization of a nonsterile site, such as the lung, or is a result of laboratory contamination. Pseudo-outbreaks of NTM have been described as a result of contamination of hospital laboratories, water supplies, and instruments such as bronchoscopes (Gubler et al., 1992). Once the diagnosis of NTM infection has been made, a treatment of long duration of is typically required (Stout, 2006). As the risk of contamination of the sputum by environmental mycobacteria is high, the misattribution of the clinical significance of a positive

The ATS/IDSA guidelines of 2007 set criteria for the diagnosis of NTM and recommend that the minimum evaluation of a patient suspected of having NTM-PD should include the following: (1) chest radiograph or, in the absence of cavitations, chest HRCT scan, (2) collection of three or more sputum specimens for acid-fast bacterium (AFB) analysis, and (3) exclusion of other disorders such as TB and lung malignancy. Furthermore, diagnosis of NTM pulmonary infection requires the fulfillment of both clinical and microbiological criteria. Clinically, it necessary that both of the following criteria are met: (1) pulmonary symptoms, nodular or cavity opacities on chest radiograph, or a HRCT scan showing multifocal bronchiectasis with multiple small nodules, and (2) appropriate exclusion of other diagnoses. Microbiologically, only one of the following criteria are required: (1) positive culture result from at least two

small, centrinodular nodules and tree-in bud opacities were seen in the all lobes.

1989; Taiwo & Glassroth, 2010).

3. Hypersensitive pneumonitis

**2.3 Diagnosis and treatment of NTM** 

contributing to the disease process (Griffith et al., 2007).

detection would lead to a useless treatment for the patient (Tortoli, 2008).

*Mycobacterium avium* complex (MAC) is the term used to describe a group of slow-growing, nonpigmented (although a yellow pigment may be produced in the absence of light) AFB (Griffith et al., 2007; Inderljed et al., 1993; Tortoli, 2006). MAC species are found worldwide, but are isolated more frequently in temperate regions, including the USA, Europe, Japan, and South Africa (Inderljed et al., 1993). MAC consists of at least two major mycobacterial species, *M. avium* and *M. intracellulare*, which cannot be differentiated on the basis of traditional physical and biochemical tests, and require specific DNA probes for identification. MAC is the most common cause of NTM infections and predominantly results in pulmonary or disseminated disease (Haverkort, 2003; Marin-Casabona et al., 2004; Thomsen et al., 2002). *M. avium* is the more important pathogen in disseminated disease, whereas *M. intracellulare* is the more common respiratory pathogen.

MAC-PD is predominantly observed in postmenopausal, non-smoking, Caucasian females (Griffith et al., 2007). In Japan, among 273 newly diagnosed MAC-PD cases between 1996 and 2002, 70.3% were female with a mean age of 63.2 years (Okumura et al., 2008). The HRCT findings of MAC-PD also exhibit all three forms of lung disease, as described for NTM-PD, namely cavitary disease, fibronodular bronchiectasis, and HP (Cappelluti et al., 2003; Embil et al., 1997; Glassroth, 2008; Kahana et al., 1997). Fibronoduar bronchiectasis caused by MAC is most frequently observed in women >60 years old, and compared to patients with other types of NTM infection, the lingual and right middle lobe tend to be more severely and progressively involved (Hollings et al., 2002; Kim et al., 2005; Kubo et al., 1998; Obayashi et al., 1999; Prince et al., 1989; Tanaka et al., 2001). In a recent clinical study, MAC was cultured from the sputum of 25% of the patients with fibronodular bronchiectasis, and MAC infection was documented in 50% of bronchoscopies, including BAL and transbronchial biopsies (Griffith et al., 2007). Although the cornerstones of MAC treatment are the macrolides clarithromycin, azithromycin, and ethambutol, MAC species are saprophytic and possess cell walls that are relatively impenetrable to an array of chemicals, endowing them with intrinsic resistance to many antimicrobials (Mdluli et al., 1998).

Nontuberculous Mycobacterium Infections in Rheumatoid Arthritis Patients 251

anti-IL-6 therapy (tocilizumab (Actemura®)). TNF-α blockers include both soluble receptors that serve as decoy receptors competing with TNF receptors (etanercept) and monoclonal antibodies that target TNF receptors (infliximab, adalimumab, golimumab, and certolizumab pegol). Anakinra is an IL-1 receptor antagonist that targets IL-1, which is an important cytokine in RA pathogenesis. Rituximab is a monoclonal antibody that selectively targets the chimeric anti-CD20, which is found primarily on B-cells. Abatacept is a recombinant human fusion protein consisting of a monoclonal antibody against CTLA-4 and a domain of CTLA-4, and serves to down-regulate T-cell activation (Salliot et al., 2009). According to the most recent meta-analysis of adverse effects of biologics based on randomized controlled trials, controlled clinical trials, and open-label extension studies, biologics as a group, after adjusting for dose, were associated with a statistically higher rate of total adverse events odds ratio (OR; 1.19) and withdrawals due to adverse events (OR 1.32), and an increased risk of TB reactivation (OR 4.68) compared to controls (Gauhar et al., 2007). Notably, TB reactivation with TNF-α blockers was drug specific, and the incidence in the biologic group was 0.149%, whereas that in control group was 0.030% (Gauhar et al., 2007). Although the risk of TB was analyzed in this report, the incidence of NTM infection was not described. However, several case reports have noted NTM-associated disease in patients receiving infliximab and etanercept (Marie et al., 2005; Mufti et al., 2005; Salvana et al., 2007; Winthrop et al., 2008), and infliximab has been statistically more increased infection ratio of mycobacterium species than etanercept (Wallis et al., 2004). There is less incidence of NTM with Infliximab than with etanercept, because infliximab binds both monomeric and trimeric forms of soluble TNF-α, whereas etanercept only binds the trimeric form. Moreover, etanercept binds less strongly to transmembrane TNF-α than infliximab

One reason for the few reports of NTM infections caused by TNF-α blocker administration may relate to the lack of evidence for a latent phase in NTM infections. In addition, NTM disease is generally insidious, occasionally difficult to diagnose, and is not required to be reported to health authorities. Furthermore, NTM infections can persist even after at least 12 months of TNF-α blocker therapy and are therefore often considered to be new infections. The generally lower pathogenicity of NTM species, as compared to *M. tuberculosis*, could further explain the lower frequency of TNF blocker-associated NTM disease (van Ingen et al., 2008). However, the frequency of NTM disease compared with TB reactivation was reported to be 5- to 10-fold higher in patients undergoing therapy with TNF-α blockers (Wallis et al., 2004). As there is no evidence for the existence of a latent phase in NTM disease, screening for NTM before initiating immunosuppressive treatment might be challenging, and is further complicated by the lack of specific tests for the detection of NTM infection. Chest radiography typically only detects diverse and partly species-specific patterns (Griffith et al., 2007); moreover, these features represent active NTM disease and cannot be used to identify early infection. Despite these difficulties, the number of NTM infections has recently exceeded that of TB (Winthrop et al., 2008), which may reflect improvements in the screening for latent TB infection (Arend et al., 2003; Beglinger et al., 2007; Carmona et al., 2005; Centers for Disease Control and Prevention, 2004; Keane &

Among the new drug classes developed for anti-RA therapy, anti-IL-17 and anti-IL-23 antibodies are particularly significant to NTM infections, as they have important roles in all stages of the immune response against mycobacterial infection, from neutrophil recruitment in early phases to granuloma formation and maintenance in later stages (Lubberts, 2008;

(Keane, 2005; Wallis et al., 2004).

Bresnihan, 2008; Leding et al., 2005).
