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24 Bioinformatics of Autoimmune Diseases
FIGURE 1.17 This owchart illustrates the sequential events leading to the development of celiac disease.
Clinically, celiac disease can present with malabsorption, diarrhea, weight loss, and irondeciency anemia. Extraintestinal features include osteoporosis, infertility, and neurological
symptoms. Dermatitis herpetiformis is a skin manifestation sharing identical immunopathology.
Diagnosis combines serologic and histologic ndings. Anti-tTG IgA is the preferred screening test.
In IgA-decient individuals, IgG-based tests such as anti-DGP are used. Diagnosis is conrmed by
duodenal biopsy, revealing villous atrophy and increased IELs. HLA testing helps exclude disease
in ambiguous cases (Rubio-Tapia etal., 2013). Treatment requires lifelong adherence to a strict
gluten-free diet, which typically leads to clinical and histological recovery. Persistent symptoms
despite compliance may indicate non-responsive celiac disease or refractory celiac disease (RCD).
TABLE 1.9
Genetic Loci Implicated in Celiac Disease
Gene/Locus Chromosome Impact on Celiac Disease
HLA-DQA1 and HLA- 6p21.3 Present in ~90–95% of patients; critical for disease; DQ2.5 homozygosity
DQB1 (DQ2.5) greatly elevates risk.
HLA-DQA1 and HLA- 6p21.3 Occurs in ~5–10% of patients; moderate risk, particularly without DQ2.
DQB1 (DQ8)
HLA-DQA1 and HLA- 6p21.3 Less common; associated with lower risk compared to DQ2.5.
DQB1 (DQ2.2)
IL2/IL21 4q27 Regulates T cells and modulates immune responses.
SH2B3 (LNK) 12q24 Regulates lymphocyte signaling; linked to autoimmune diseases.
CCR2 3p21 Chemokine receptor involved in immune cell trafcking and inammation.
LPP 3q28 Involved in cell adhesion; rs1464510 raises risk by ~30%.
PTPN2 18p11 Regulates T-cell activation; linked to multiple autoimmune conditions.
TAGAP 6q25 Regulates T-cell activation; linked to celiac disease.
IL18RAP 2q12 Plays a role in inammatory response; associated with disease risk.
RGS1 1q31 Regulates B cell activation; linked to celiac disease immunity.
TGM2 (transglutaminase 2) 20q11.2 Encodes the autoantigen targeted by anti-tTG antibodies; central to disease
pathology.
25 Immune Mechanisms and Major Autoimmune Diseases
RCD type II carries a risk for enteropathy-associated T-cell lymphoma (EATL) and may require
immunosuppressive therapy (Green & Cellier, 2007).
Emerging therapies (such as gluten-degrading enzymes, tight junction modulators like larazotide
acetate, and tolerance-inducing vaccines) are under investigation. However, no pharmacological
alternative yet surpasses the gluten-free diet as standard care. Early diagnosis and patient education
remain essential to prevent long-term complications.
1.3.6 HASHIMOTO’S THYROIDITIS
Hashimoto’s thyroiditis (HT), or chronic lymphocytic thyroiditis, is the most common autoimmune thyroid disorder and a leading cause of hypothyroidism in iodine-sufcient regions (McLeod
& Cooper, 2012). It is characterized by progressive autoimmune destruction of the thyroid gland,
mediated by both T cells and autoantibodies, particularly antithyroid peroxidase (anti-TPO) and
anti-thyroglobulin (anti-Tg) antibodies. The disease shows a strong female predominance and typically manifests between ages 30 and 50.
The pathogenesis of HT involves both genetic susceptibility and environmental triggers. Key
genetic associations include HLA-DR3, HLA-DR5, and non-HLA genes such as CTLA4, PTPN22,
and FOXP3, which contribute to impaired immune tolerance and T-cell dysregulation (Tomer &
Huber, 2009). Environmental contributors include excess iodine intake, viral infections (e.g., EBV,
hepatitis C), radiation, and certain medications (e.g., interferon-α, amiodarone) (Ralli etal., 2020;
Zimmermann & Boelaert, 2015).
Figure 1.18 depicts the immunopathogenic sequence: in genetically predisposed individuals,
environmental factors trigger loss of tolerance. Autoreactive CD4+ T cells recognize thyroid antigens (TPO and Tg), activating CD8+ cytotoxic T cells and B cells, which produce high-afnity
autoantibodies. The result is progressive thyroid tissue destruction through cytokine-mediated
inammation, apoptosis, and antibody-dependent cellular cytotoxicity.
Table 1.10 summarizes key genetic loci associated with HT. HLA alleles (e.g., HLA-DRB1 and
DRB4) inuence antigen presentation. Non-HLA genes such as CTLA4, PTPN22, TG, TPO, and
TSHR contribute to immune dysregulation and thyroid-specic autoimmunity. Additional loci
include CD247, BACH2, and FOXP3, highlighting the polygenic nature of HT (Tomer & Huber,
2009).
FIGURE 1.18 This owchart illustrates the sequential events leading to the development of Hashimoto’s
thyroiditis.
26 Bioinformatics of Autoimmune Diseases
TABLE 1.10
Key Genetic Loci Associated with Hashimoto’s Thyroiditis
Gene/Locus Chromosome Role in Hashimoto’s Thyroiditis
HLA-DRB1 6p21.3 Encodes MHC class II; DR3 and DR5 alleles increase HT risk by altering
(e.g., DR3, DR5) antigen presentation.
HLA-DRB4 (DR53) 6p21.3 Associated with HT; inuences immune response through antigen
presentation.
CTLA4 2q33 Encodes CTLA-4; variants may disrupt T-cell regulation and promote
autoimmunity.
PTPN22 1p13.2 Encodes lymphoid tyrosine phosphatase; variants alter TCR signaling and
increase autoimmune risk, including HT.
TG (thyroglobulin) 8q24 Encodes thyroglobulin; variants may alter expression and trigger thyroid
autoimmunity.
TSHR (thyroid-stimulating 14q31 Encodes the TSH receptor; polymorphisms may alter thyroid function and
hormone receptor) immune recognition, contributing to HT pathogenesis.
CD247 1q24 Encodes CD3 zeta, a TCR component linked to T-cell activation and HT
susceptibility.
TPO (thyroid peroxidase) 2p25 Encodes thyroid peroxidase, crucial for hormone synthesis; target of
autoantibodies in Hashimoto’s thyroiditis.
BACH2 6q15 Transcription factor; variants may affect B cell function and autoimmunity.
FOXP3 Xp11.23 Encodes a transcription factor essential for Treg development; mutations
impair tolerance and promote autoimmunity.
TBX1 22q11.21 Involved in pharyngeal development; deletions increase risk of HT-associated
syndromes.
UBE2L3 22q11.21 Encodes a ubiquitin enzyme linked to immune regulation and higher HT risk.
Clinically, HT may present with fatigue, cold intolerance, weight gain, constipation, bradycardia, and menstrual irregularities. A goiter may be present in early stages. Some patients experience a transient hyperthyroid phase (Hashitoxicosis) due to follicular rupture. Diagnosis is based
on elevated TSH, low or normal free T4, and high titers of anti-TPO (present in >90% of cases).
Thyroid ultrasound typically shows a hypoechogenic, heterogeneous gland. In unclear cases, neneedle aspiration may help conrm autoimmune thyroiditis. Treatment involves levothyroxine
to normalize TSH and alleviate symptoms. Dosing is individualized and titrated with periodic
TSH monitoring. Some patients with persistent symptoms despite normal TSH may require further evaluation or adjusted therapy, although combination therapy with liothyronine (T3) remains
controversial.
Emerging approaches focus on immune modulation. These include low-dose naltrexone, selenium (in decient individuals), and vitamin D optimization. Investigational therapies such as
antigen-specic immunomodulation, Treg induction, and gut microbiome modulation aim to treat
the autoimmune basis rather than just hormone deciency.
HT exemplies organ-specic autoimmunity, where complex genetic, environmental, and immunological factors lead to endocrine dysfunction. Despite effective hormone replacement, research
continues toward disease-modifying therapies that address the underlying immune dysregulation.
1.3.7 GRAVES’ DISEASE
Graves’ disease is an organ-specic autoimmune thyroid disorder and the most common cause of
hyperthyroidism in iodine-sufcient regions (Smith & Hegedüs, 2016). The hallmark feature is
the presence of thyroid-stimulating immunoglobulins (TSIs), autoantibodies that mimic TSH by
27 Immune Mechanisms and Major Autoimmune Diseases
FIGURE 1.19 This owchart illustrates the sequential events leading to the development of Graves’ disease.
binding to the TSH receptor (TSHR), resulting in unregulated thyroid hormone production and
thyrotoxicosis.
Pathogenesis involves genetic susceptibility and immune dysregulation, shaped by environmental factors. Key genetic associations include HLA-DR3, HLA-DQA1*0501, and immune-regulatory
genes such as CTLA4, PTPN22, and CD40 (Tomer & Davies, 2003). Environmental triggers (such
as stress, smoking, infections (e.g., EBV), and iodine excess) can disrupt immune tolerance in predisposed individuals. The disease has a strong female predominance, likely inuenced by estrogen
and X-linked immune genes.
Figure 1.19 outlines the disease cascade: genetic predisposition combined with environmental
exposure leads to T cell-mediated activation of autoreactive B cells, which secrete TSIs. These stimulate thyroid follicular cells, causing hyperplasia, goiter, and increased T3 and T4 production. TSIs
also affect broblasts, contributing to Graves’ orbitopathy and, less commonly, pretibial myxedema.
Table 1.11 summarizes key genetic loci associated with Graves’ disease. In addition to HLA-
DRB1, CTLA4, and PTPN22, variants in TSHR, TG, CD40, FOXP3, and IL2RA modulate immune
tolerance and thyroid antigenicity (Plagnol etal., 2011).
Clinically, Graves’ disease presents with thyrotoxicosis (e.g., weight loss, heat intolerance, anxiety, tachycardia) and extrathyroidal features, particularly Graves’ orbitopathy (seen in 25–50% of
patients), and rarely, dermopathy. Orbitopathy results from autoimmune activation of orbital broblasts, causing proptosis, diplopia, and periorbital edema. Diagnosis is supported by elevated free
T3/T4, suppressed TSH, and positive TSIs or TRAb. Ultrasound typically reveals an enlarged,
vascular thyroid; radionuclide uptake scans conrm diffuse hyperactivity. Treatment options for
hyperthyroidism include anti-thyroid drugs such as methimazole or propylthiouracil (PTU), which
work by inhibiting thyroid hormone synthesis. These medications may induce remission, although
relapse is common. Radioactive iodine (RAI) therapy offers a denitive, non-surgical approach
by ablating the thyroid gland; however, it is contraindicated in pregnancy and in patients with
active thyroid eye disease (orbitopathy). Surgical intervention, typically in the form of total or
near-total thyroidectomy, is reserved for cases involving large goiters, compressive symptoms, or
when preferred by the patient. Management of Graves’ orbitopathy involves ophthalmologic support. Mild cases may benet from selenium and lifestyle changes, while moderate-to-severe disease
may require steroids, orbital radiation, or teprotumumab, a monoclonal antibody targeting IGF-1R
(Smith etal., 2017).
28 Bioinformatics of Autoimmune Diseases
TABLE 1.11
Key Genetic Loci Associated with Graves’ Disease
Gene/Locus Chromosome Impact on Graves’ Disease
HLA-DRB1/ 6p21.3 MHC class II alleles linked to higher risk; mediate antigen presentation to
HLA-DQA1 T cells.
CTLA4 2q33 Encodes a T-cell inhibitor; variants disrupt immune tolerance.
PTPN22 1p13.2 Encodes a lymphoid phosphatase; rs2476601 variant linked to multiple
autoimmune diseases, including GD.
TSHR 14q31 Encodes the TSH receptor; variants alter expression and immune
recognition.
FCRL3 1q23 Regulates B cells; variants linked to GD risk.
CD40 20q11.2 Co-stimulatory protein on APCs; variants may amplify immune
responses.
TG (thyroglobulin) 8q24.22 Major thyroid autoantigen; variants may affect autoantibody levels.
RNASET2-FGFR1OP- 6q27 GWAS-identied locus linked to immune regulation and GD risk.
CCR6
CHRNA9 4p14 Nicotinic acetylcholine receptor subunit; GD-associated GWAS locus.
IL2RA 10p15.1
FOXP3 Xp11.23 Essential transcription factor for Treg development; mutations disrupt
GPR174 Xq21.1 G protein-coupled receptor; variant linked to male GD risk.
BTNL2 6p21.32 Butyrophilin-like 2: Regulates T cells; variants associated with Graves’
SCGB3A2/UGRP1 5q32 Secretoglobin family protein linked to immune response in GD.
Encodes IL-2 receptor α; variants affect immune regulation in GD.
immune tolerance.
disease.
In summary, Graves’ disease exemplies a systemic autoimmune condition with both thyroidal
and extrathyroidal involvement. Advances in genetics, immunology, and therapeutics have improved
management strategies and supported the shift toward personalized care.
1.3.8 INFLAMMATORY BOWEL DISEASES
Inammatory bowel diseases (IBDs), including Crohn’s disease and ulcerative colitis, are chronic
autoimmune disorders characterized by recurrent inammation of the gastrointestinal (GI) tract.
Affecting millions worldwide, IBD incidence has risen sharply in industrialized nations, implicating environmental factors acting on a genetically susceptible background (Ananthakrishnan, 2015).
Although these conditions share symptoms such as abdominal pain and diarrhea, they differ markedly in their anatomical distribution, histopathology, and immunological mechanisms.
IBD pathogenesis reects a multifactorial process involving host genetics, microbial dysbiosis,
immune dysregulation, and environmental exposures. GWAS have identied over 200 susceptibility loci, including disease-specic and shared genes. Notably, mutations in NOD2, a microbial
sensor, impair recognition of bacterial peptidoglycan, contributing to a pro-inammatory milieu
in Crohn’s disease (Ogura et al., 2001). Other key genes include ATG16L1, involved in autoph-
agy, and IL23R, regulating Th17 cell differentiation (Jostins etal., 2012). Environmental modi-
ers include early antibiotic exposure, smoking, and NSAID use. Smoking paradoxically increases
the risk of Crohn’s disease while exerting a protective effect in ulcerative colitis (Cosnes et al.,
2001). Broad-spectrum antibiotics, especially in early life, may disrupt microbiome development,
fostering long-term immune dysfunction. Gut microbial dysbiosis is central to disease progression. IBD patients exhibit reduced microbial diversity, loss of anti-inammatory taxa such as
Faecalibacterium prausnitzii, and expansion of pro-inammatory organisms like adherent-invasive
29 Immune Mechanisms and Major Autoimmune Diseases
FIGURE 1.20 This owchart illustrates the sequential events leading to the development of Inammatory
bowel diseases.
Escherichia coli (Frank etal., 2007). These changes impair epithelial barrier function and promote
mucosal immune activation.
Figure 1.20 illustrates the IBD pathogenic cascade: genetic mutations (e.g., NOD2, ATG16L1,
IL23R) compromise mucosal immunity and tolerance, while environmental insults further disrupt
homeostasis. Dysbiosis activates DCs and macrophages, leading to CD4+ T-cell polarization toward
Th1 and Th17 phenotypes. The resulting cytokines (TNF-α, IL-17, and IL-23) drive chronic inammation, neutrophil inltration, and tissue damage. In Crohn’s disease, inammation is transmural
and segmental; in ulcerative colitis, it is conned to the mucosa and rectum.
Table 1.12 outlines key genetic contributors to IBD. NOD2 (16q12) affects innate bacterial sens-
ing, IL23R (1p31) modulates Th17 immunity, and autophagy genes such as ATG16L1 and IRGM
inuence microbial clearance (Duerr etal., 2006; Hampe etal., 2007). HLA class II alleles, espe-
cially in ulcerative colitis, alter antigen presentation (Jostins etal., 2012). Additional loci include
cytokine genes (e.g., IL10, TNFSF15, STAT3), mucosal regulators (e.g., PTGER4), and transcriptional regulators (e.g., NKX2-3, FOXP3).
Crohn’s disease can involve any GI region, with terminal ileum involvement most common.
Transmural inammation leads to complications such as strictures, stulas, and abscesses.
Ulcerative colitis affects the colon in a continuous pattern, with inammation restricted to the
mucosa. Diagnosis requires endoscopy and biopsy, supported by non-invasive biomarkers such as
fecal calprotectin and C-reactive protein (CRP). Treatment goals include inducing and maintaining
remission, promoting mucosal healing, and preventing complications. For mild ulcerative colitis,
aminosalicylates like mesalamine are rst-line agents. In moderate-to-severe cases, corticosteroids provide rapid relief but are unsuitable for long-term use due to systemic toxicity (Sandborn
& Hanauer, 2003). Immunomodulators such as azathioprine offer steroid-sparing maintenance but
require regular monitoring.
The advent of biologic therapies has signicantly transformed the management of IBD. Among
these are anti-TNF agents, such as iniximab and adalimumab, which block TNF-α–mediated
inammation. Anti-integrin therapies, like vedolizumab, work by preventing leukocyte trafcking
to the gut, thereby reducing intestinal inammation. Additionally, IL-12/23 inhibitors, including
ustekinumab, target cytokine pathways critical to T-cell activation (Feagan etal., 2016). Another
class of therapies, Janus kinase (JAK) inhibitors such as tofacitinib, offers an oral treatment
option that interferes with intracellular cytokine signaling. Although JAK inhibitors have shown
30 Bioinformatics of Autoimmune Diseases
TABLE 1.12
Key Genetic Loci in Inammatory Bowel Disease (IBD), Including Crohn’s Disease (CD)
and Ulcerative Colitis (UC)
Gene/Locus Chromosome IBD Subtype(s) Functional Impact
NOD2 (CARD15) 16q12 CD Recognizes bacterial peptidoglycan; mutations weaken
innate immunity and raise CD risk.
IL23R 1p31 CD and UC Encodes IL-23 receptor; variants inuence Th17
differentiation and inammation.
ATG16L1 2q37 CD Autophagy-related; T300A variant disrupts bacterial
clearance and Paneth cell function.
IRGM 5q33 CD Regulates autophagy; variants impair pathogen clearance.
HLA Region 6p21 UC Major histocompatibility complex: specic alleles shape
antigen presentation and immune activity.
IL10 1q32 CD and UC Anti-inammatory cytokine; mutations cause intestinal
inammation.
TNFSF15 9q32 CD Encodes TL1A, a cytokine regulating T cells; variants
linked to inammation.
PTGER4 5p13 CD Prostaglandin E receptor: variants may alter mucosal
integrity and immune response.
NKX2-3 10q24 CD and UC Transcription factor for gut development; variants may
impair barrier integrity.
STAT3 17q21 UC Mediates cytokine signaling; mutations affect immune cell
differentiation and function.
effectiveness in ulcerative colitis, their use requires careful patient selection due to potential safety
concerns, particularly the increased risk of thrombotic events (Sandborn etal., 2017).
Microbiota-based interventions such as fecal microbiota transplantation (FMT) and targeted
probiotic therapies are under active investigation. Exclusive enteral nutrition (EEN) is an effective
induction strategy in pediatric Crohn’s disease. Dietary regimens like SCD and low FODMAP
may improve symptoms, though their role in inammatory control is still emerging (Suskind
etal., 2014).
Despite therapeutic advances, many patients experience relapse or primary non-response, underscoring the need for precision medicine approaches. Integrating genomics, proteomics, and microbiome proling may enable personalized interventions and improved outcomes.
In conclusion, IBD reects a multifaceted breakdown in mucosal immunity, shaped by genetic,
microbial, and environmental factors. While current therapies have greatly improved disease control, continued research is needed to develop curative, patient-specic treatments.
1.3.9 PSORIASIS
Psoriasis is a chronic, immune-mediated inammatory skin disorder that affects approximately
2–3% of the global population. It typically manifests as sharply demarcated, erythematous
plaques with overlying silvery-white scales, often appearing on the extensor surfaces such as
the elbows, knees, and scalp. Additional sites may include the lower back, nails, and genital
region. While traditionally classied as a dermatologic disease, psoriasis is now increasingly
recognized as a systemic inammatory condition, frequently associated with psoriatic arthritis,
metabolic syndrome, cardiovascular disease, and substantial psychosocial burden (Boehncke &
Schön, 2015).
31 Immune Mechanisms and Major Autoimmune Diseases
The pathogenesis of psoriasis involves a complex interplay of genetic susceptibility, immune
dysregulation, and environmental triggers. A key immunologic pathway implicated in disease
progression is the interleukin-23 (IL-23)–interleukin-17 (IL-17) axis. DCs produce IL-23, which
promotes the differentiation and maintenance of T helper 17 (Th17) cells. These cells secrete proinammatory cytokines (IL-17A, IL-17F, and IL-22) that act on keratinocytes to induce hyperproliferation, impair terminal differentiation, and stimulate the release of antimicrobial peptides and
chemokines (Gaffen etal., 2014). IL-22 plays a particularly important role in promoting epidermal
thickening and compromising barrier integrity.
Genetic contributions to psoriasis are substantial, with heritability estimates ranging from 60
to 90%. GWAS have identied over 60 susceptibility loci, many involving immune-related genes.
The HLA-C*06:02 allele is the most strongly associated variant, especially in early-onset cases.
Other implicated loci include IL23R, encoding the IL-23 receptor, and TNFAIP3, encoding A20, a
negative regulator of the NF-κB pathway. These genetic variants likely contribute to the persistent
inammatory loop characteristic of chronic disease.
Environmental and lifestyle factors modify disease onset and severity. The Koebner phenomenon, in which trauma to the skin elicits psoriatic lesions, is observed in up to 25% of patients.
Streptococcal infections, particularly in children and adolescents, are strongly associated with guttate psoriasis. HIV and other infections can also exacerbate disease severity. Medications such as
lithium, beta-blockers, antimalarials, and withdrawal from systemic corticosteroids are recognized
triggers. Additionally, psychological stress, alcohol use, and obesity signicantly inuence disease
activity and therapeutic response (Setty etal., 2007).
Figure 1.21 illustrates the immunopathogenic cascade underlying psoriasis. Genetic predisposi-
tion (especially involving HLA-C*06:02) interacts with environmental insults such as infections
or trauma to activate keratinocytes. These cells release danger signals that recruit plasmacytoid
dendritic cells (pDCs), which in turn secrete type I interferons, activating myeloid dendritic cells
(mDCs). mDCs produce IL-12 and IL-23, driving the differentiation of Th1 and Th17 cells. These
T cells inltrate the skin and release cytokines, including IL-17, IL-22, and TNF-α, which act on
keratinocytes to sustain hyperproliferation and inammation, ultimately resulting in the formation
of psoriatic plaques.
Table 1.13 summarizes major susceptibility genes and loci in psoriasis, along with their chromo-
somal positions and biological roles. Key loci identied by GWAS include HLA-C06:02*, IL12B,
FIGURE 1.21 Pathogenic pathway leading to the development of psoriasis.
32 Bioinformatics of Autoimmune Diseases
TABLE 1.13
Major Genes and Loci Implicated in Psoriasis
Gene/Locus Chromosome Role in Psoriasis Pathogenesis
HLA-C (HLA-C*06:02) 6p21.3 MHC class I allele; top genetic risk for psoriasis presents antigens to CD8
Tcells.
CCHCR1 6p21.3 Encodes a coiled-coil protein linked to keratinocyte growth and differentiation.
CDSN 6p21.3 Encodes corneodesmosin; supports skin barrier and keratinocyte adhesion.
IL12B 5q33.3 Encodes p40 subunit of IL-12/IL-23; drives Th1/Th17 responses.
IL23R 1p31.3 Encodes IL-23 receptor; essential for Th17 differentiation.
TNIP1 5q33.1
TNFAIP3 6q23.3
TRAF3IP2 6q21 Encodes IL-17 pathway adaptor; modulates Th17-driven inammation.
CARD14 17q25.3
LCE3B/LCE3C 1q21.3 Late cornied envelope genes: deletions impair skin barrier.
S100A7A (koebnerisin) 1q21.3 Encodes an antimicrobial peptide; overexpressed in psoriasis, driving
IL36G 2q13
DDX58 9p21.1 Encodes RIG-I, a cytosolic PRR involved in psoriasis-related innate immunity.
TYK2 19p13.2 Encodes TYK2, mediating IL-23 and type I interferon signaling.
Inhibits NF-κB signaling to regulate inammation.
Encodes A20, a negative regulator of NF-κB–mediated inammation.
Encodes a scaffold protein activating NF-κB in keratinocytes; mutations linked
to familial psoriasis.
inammation.
Encodes IL-36γ; drives keratinocyte activation and inammation.
+
IL23R, TNIP1, CARD14, and others involved in T-cell activation, cytokine regulation, and keratinocyte signaling (Bowcock & Krueger, 2005; Tsoi etal., 2012).
Diagnosis is primarily clinical, based on characteristic lesion morphology and distribution.
Classic plaques are erythematous with silvery scale, often on the extensor surfaces and scalp.
Additional features include nail pitting, onycholysis, and the Auspitz sign—pinpoint bleeding when
scales are removed. In atypical cases, where clinical features resemble eczema, dermatophytosis,
or cutaneous lymphoma, a biopsy may aid diagnosis. Histopathological features include acanthosis (epidermal thickening), parakeratosis, elongation of rete ridges, and dense dermal lymphocytic
inltration. The presence of Munro microabscesses (neutrophil aggregates within the stratum corneum) is considered pathognomonic (Lowes etal., 2014). Treatment depends on disease severity,
lesion distribution, and comorbid conditions. For mild-to-moderate cases, topical agents remain
rst-line therapy, including corticosteroids, vitamin D analogs, calcineurin inhibitors, and coal tar.
These reduce inammation, normalize keratinocyte function, and relieve pruritus. Moderate-tosevere psoriasis requires systemic treatment. Traditional agents include methotrexate, cyclosporine,
and acitretin, though their use is limited by potential toxicity and teratogenicity.
The introduction of biologic therapies has revolutionized the management of immune-mediated
inammatory diseases by offering targeted, mechanism-based treatments. These include TNF-α
inhibitors such as etanercept, adalimumab, and iniximab, which block a key pro-inammatory
cytokine. IL-12/23 inhibitors like ustekinumab, IL-17 inhibitors such as secukinumab and ixekizumab, and IL-23 inhibitors including guselkumab and risankizumab further expand the therapeutic arsenal by targeting distinct cytokine pathways involved in immune dysregulation. These
biologics have demonstrated superior efcacy, durable remission, and signicant improvements in
patients’ quality of life (Grifths etal., 2021). However, despite their clinical benets, important
challenges remain regarding high treatment costs, limited accessibility, and the need for ongoing
long-term safety monitoring.
Personalized medicine approaches are increasingly emphasized, tailoring treatment to disease
subtype, molecular prole, and individual patient needs. Lifestyle modications such as weight
33 Immune Mechanisms and Major Autoimmune Diseases
reduction, alcohol moderation, and stress reduction can improve treatment outcomes and reduce
are frequency (Kimball etal., 2005).
Psoriasis is now regarded as a systemic inammatory disease with increased risk for metabolic
syndrome, cardiovascular disease, depression, and IBD. Thus, interdisciplinary care is essential to
address comorbidities.
Ongoing research is uncovering new therapeutic avenues. Investigations into the skin microbiome, neuroimmune communication, and immune tolerance restoration offer promise. Technologies
such as single-cell transcriptomics and multi-omics proling are providing deeper insights into
disease heterogeneity, mechanisms of treatment resistance, and individualized care.
Although psoriasis remains incurable, the expanding therapeutic landscape and improved
understanding of disease biology offer hope for more precise, effective, and durable management
strategies.
1.3.10 MYASTHENIA GRAVIS
Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disorder characterized by uctuating skeletal muscle weakness and fatigability due to impaired synaptic transmission at the
neuromuscular junction. Although MG is relatively rare, its estimated global prevalence is approximately 20 cases per 100,000 individuals, with notable geographic and ethnic variation (Carr etal.,
2010). The disease exhibits a bimodal age distribution, with higher incidence in women under 40
and men over 60, suggesting roles for hormonal inuences and immunosenescence in pathogenesis. The hallmark clinical feature of MG is fatigable muscle weakness, whereby muscle strength
declines with sustained exertion and improves with rest. This mirrors the underlying failure of neuromuscular transmission. In most cases, MG is mediated by autoantibodies targeting the nicotinic
acetylcholine receptors (AChRs) located on the postsynaptic membrane. These antibodies impair
neuromuscular transmission by three synergistic mechanisms: direct receptor blockade, antigenic
modulation via internalization, and complement-mediated destruction of the postsynaptic membrane (Gilhus etal., 2019).
Approximately 10–15% of MG patients who test negative for AChR antibodies are positive for
antibodies against muscle-specic kinase (MuSK), a receptor tyrosine kinase essential for AChR
clustering. MuSK-positive MG often presents with prominent bulbar symptoms such as dysarthria,
dysphagia, and respiratory weakness and may respond differently to standard therapies. Additional
autoantibodies, including those against LRP4 and agrin, have been identied in smaller subsets,
expanding the immunopathologic spectrum of MG.
Genetic predisposition plays a contributory role, although MG is not inherited in a simple
Mendelian fashion. Strong associations exist with HLA class II alleles, especially HLA-DR3 and
HLA-B8, particularly in early-onset AChR-positive cases. Polymorphisms in immune regulatory genes such as CTLA4 and PTPN22 have also been implicated, underscoring the relevance of
broader autoimmune susceptibility pathways. However, genetic susceptibility alone is insufcient
for disease development, implicating environmental triggers in the breakdown of immune tolerance.
Among environmental factors, viral infections (particularly EBV) are suspected triggers via
molecular mimicry and bystander activation. The thymus gland plays a central role in MG pathogenesis, especially in early-onset AChR-positive MG. Approximately 70% of these patients show
thymic hyperplasia with germinal center formation, while 10–15% develop thymomas. The thymus
serves as an ectopic site of antigen presentation and autoreactive lymphocyte maturation, contributing to the autoimmune response (Lindstrom etal., 2008).
Figure 1.22 presents the immunopathogenic cascade underlying MG. In genetically suscepti-
ble individuals, environmental and physiological insults, such as infection or stress, can disrupt
immune regulation, allowing autoreactive T and B cells to escape central and peripheral tolerance.
Activated CD4+ helper T cells promote B-cell clonal expansion and antibody production against
neuromuscular targets, primarily AChRs. These autoantibodies initiate receptor internalization,
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