**2. Diaeventological sources of GAD**

During early stages of embryo implantation, there is a suggested suppression of the immune response; yet, there are many immune systems at play. These include NK cells. NKs are innate immune cells that require no secondary or tertiary recombination and adaptation to kill target cells upon antigen presentation as with Major Histocompatibility Complex (MHC) class I-held antigens [3]. This allows NK cells to degranulate and release cytotoxic substances directly into targeted cells for destruction. There is a pull back, or switch, that may involve mesenchymal stem cells signaling through interferon that regulate and therefore license and delicense the NK killing based on chemokine reception and a global on/off switch [3].

A recent report catalogs some of the descriptors of immune surveillance in the uterus. In this chapter, it is reported that macrophages, NK cells, and T cells are found in the human decidua [3]. Over 70% of the detectable immune cells are NKs and the rest are mostly macrophages with small percentages of dendritic cells. They also summarize from the literature that no B or plasma cells can be detected. However, the remainder of the immune cell population is of T-cell lineage.

Of interest to the argument that the diaeventome drives an epigenetically modifiable immune-based regulation of global physiological and pathophysiological consequence is that the ablation of NK cells prevents trophoblasts from obtaining endometrial vascularity. This results in spontaneous abortion. Whether this phenomenon is associated with controlled cell destruction or chemokine/cytokine-mediated signaling, leading to reprogramming of gene expression, is not yet clear, but it does suggest that NK cells may be necessary for in utero trophoblast invasion. Since dendritic cells play a key role in communication between the constitutive and adaptive immune response, it is of further note that loss of uterine Dendritic Cell (DCs) blocks decidual maturation and blastocyst implantation [3].

aerobic glycolysis and can be triggered by the bacterial antigen LPS ± the pro-inflammatory cytokine IFN-γ. Within the anti-inflammatory lineage, IL-4 induces the expression of PPARγ which in turn transcriptionally activates the urea cycle enzyme arginase 1 (Arg1) and the β-oxidation of fatty acids along with electron transport chain/oxidative phosphorylation gene expression and an increased capacity for mitochondrial biogenesis [7]. To fuel the anti-inflammatory bioenergetics, IL-4 also induces expression of CD36 which acts as a membrane receptor for circulating LDL and very low density lipoprotein (VLDL)-rich triacylglycerol (TAG)**.** Finally, the unloading of triacylglycerol (TAG) and associated fatty acid hydrolase activity is linked to

The Diaeventology of Anxiety Disorders http://dx.doi.org/10.5772/intechopen.82176 17

fatty acid oxidation, thus completing the anti-inflammatory polarization phenotype [7].

genesis in the region [11].

the HPA axis [12].

Recently, a macrophage-specific cytokine has been linked to anxiety. The macrophage migration inhibitory factor (MIF) is a pro-inflammatory macrophage-specific cytokine that is active in the HPA axis and characterized haplotype variants of that gene were linked to diminished expression and lowered adolescent anxiety disorder [8]. MIF has been linked to the recruitment of natural killer T cells via an IFN-γ gradient in skin lesions, thus suggesting a similar role in causing the migration and stimulation of inflammatory leucocytes in the HPA axis [9]. Indeed, MIF has been implicated with this dual cytokine/chemokine role in a large cluster of inflammatory diseases, thus suggesting a global immunopathological association of macrophages and other leucocytes in neuropsychiatric disease [10]. A previous report suggested that deletion or pharmacological inhibition of MIF biological activity in the hippocampal gyrus of mice resulted in anxiety-like behavior and this was correlated with a lack of neuro-

Combined, this evidence on macrophage switching, inflammation, and neurogenesis (thus targeting the canonical HPA axis) all point to a diaeventological progression of both environmental and genetic plus epigenetic event ontologies that instantiate a temporal link to anxiety disorders.

The serotonin transporter (HTTPLPR) has been linked to depression and GAD in human populations. The short allele of the HTTPLPR gene was associated with these neuropsychiatric disorders although whether there was a hypo- or hyper-HPA axis effect depended upon the cohort population under study including parameters age, race, and gender [12]. However, this is not necessarily ambiguous, since the downstream processing of serotonin binding to its receptor is complicated by the level of allele-specific HTTPLPR-mediated translocation, availability of serotonin, plus the receptor subtype, and ultimate release of glucocorticoid via

There are serotonin receptors on macrophages, monocytes, and lymphocytes, and these subpopulations interact to mediate inflammatory responses leading to HPA axis activity [13].

Serotonin has been associated with a blockade of the antigenic determinate capacity of macrophages via IFN-γ, thus diminishing the suppression of NK cells and therefore enhancing their

**3. Acquired neuroimmune responses and GAD**

potential cytotoxic function on host cells [13].

Stress can induce epigenetic changes to loci that control the expression of RNAi production. RNAi epigenetics involves the production of interfering RNA species and thus prevents target mRNA expression. This removal of target mRNA can have global or specific effects on gene expression including those involved in psychiatric and mood disorders [4].

Even though chronic psychological and social stress has been implicated in anxiety disorders, the mechanism for how social defeat and worrying can be linked to genomic or epigenomic phenomena has been difficult to track.

Recently, it was reported that chronic stress in a murine model was targeting an RNASE II enzyme complex (DROSHA subunit) via differential hypomethylation at that locus. A decrease in methylation suggests there is a concomitant increase in the non-specific expression of the target gene, and in this case, it would mean an increase in RNAi-mediated epigenetic ablation of gene expression [5].

In a rat model, pro-inflammatory CNS-localized M1 type microglia are induced by cumulative unpredictable mild stress (CUMS) within the Hypothalamic Pituitary Adrenal (HPA) axis [6]. This resulted in the expression of pro-inflammatory tumor necrosis factor (TNF)-α, interferon (INF)-γ, interleukin (IL)-1β, and IL-17 cytokines while simultaneously reducing the production of the anti-inflammatory IL-4, IL-10, and IL-13 cytokines typically associated with the regulatory M2 microglial lineage [6].

Macrophages are classified into inflammatory or anti-inflammatory. Inflammatory macrophages differentiate in response to microbial and tumor antigens and interferon γ by producing pro-inflammatory cytokines at the site of nascent infection and cancerous lesions while anti-inflammatory macrophages differentiate via signaling by glucocorticoids or anti-inflammatory (type II) cytokines like IL-4, IL-13, and IL-10 where they promote TH2 immunity and mediate tissue remodeling, wound healing, and immune modulation [7].

The cytokines IL-4 and IL-13 drive anti-inflammatory macrophage polarization through the IL-4 receptor alpha chain (IL-4Rα), and anti-inflammatory polarization is also promoted by activation of several master regulators, including signal transducer and activator of transcription 6 (STAT6), Krüppel-like factor 4 (KLF4), and interferon regulatory factor 4 (IRF4) [7].

Diet and nutritional life style choices likely modulate macrophage polarization and, by inference, the inflammatory response associated with anxiety disorder. Bioenergetic reprogramming is associated with this mechanism wherein the inflammatory macrophage cell type is fueled by aerobic glycolysis and can be triggered by the bacterial antigen LPS ± the pro-inflammatory cytokine IFN-γ. Within the anti-inflammatory lineage, IL-4 induces the expression of PPARγ which in turn transcriptionally activates the urea cycle enzyme arginase 1 (Arg1) and the β-oxidation of fatty acids along with electron transport chain/oxidative phosphorylation gene expression and an increased capacity for mitochondrial biogenesis [7]. To fuel the anti-inflammatory bioenergetics, IL-4 also induces expression of CD36 which acts as a membrane receptor for circulating LDL and very low density lipoprotein (VLDL)-rich triacylglycerol (TAG)**.** Finally, the unloading of triacylglycerol (TAG) and associated fatty acid hydrolase activity is linked to fatty acid oxidation, thus completing the anti-inflammatory polarization phenotype [7].

Recently, a macrophage-specific cytokine has been linked to anxiety. The macrophage migration inhibitory factor (MIF) is a pro-inflammatory macrophage-specific cytokine that is active in the HPA axis and characterized haplotype variants of that gene were linked to diminished expression and lowered adolescent anxiety disorder [8]. MIF has been linked to the recruitment of natural killer T cells via an IFN-γ gradient in skin lesions, thus suggesting a similar role in causing the migration and stimulation of inflammatory leucocytes in the HPA axis [9]. Indeed, MIF has been implicated with this dual cytokine/chemokine role in a large cluster of inflammatory diseases, thus suggesting a global immunopathological association of macrophages and other leucocytes in neuropsychiatric disease [10]. A previous report suggested that deletion or pharmacological inhibition of MIF biological activity in the hippocampal gyrus of mice resulted in anxiety-like behavior and this was correlated with a lack of neurogenesis in the region [11].

Combined, this evidence on macrophage switching, inflammation, and neurogenesis (thus targeting the canonical HPA axis) all point to a diaeventological progression of both environmental and genetic plus epigenetic event ontologies that instantiate a temporal link to anxiety disorders.
