Molecular mimicry in autoimmune disease

Epitope Spreading in Immune-Mediated Glomerulonephritis: The Expanding Target

Epitope spreading is a critical mechanism driving the progression of autoimmune glomerulonephritis. This phenomenon, where immune responses broaden from a single epitope to encompass additional targets, contributes to the complexity and severity of diseases such as membranous nephropathy (MN), lupus nephritis (LN), and ANCA-associated vasculitis (AAV). In MN, intramolecular spreading within the phospholipase A2 receptor correlates with a worse prognosis, while LN exemplifies both intra- and intermolecular spreading, exacerbating renal involvement. Similarly, ANCA reactivity in AAV highlights the destructive potential of epitope diversification. Understanding these immunological cascades reveals therapeutic opportunities-targeting early epitope spreading could curb disease progression. Despite promising insights, the clinical utility of epitope spreading as a prognostic tool remains debated. This review provides a complete overview of the current evidence, exploring the dual-edged nature of epitope spreading, the intricate immune mechanisms behind it, and its therapeutic implications. By elucidating these dynamics, we aim to pave the way for more precise, targeted interventions in autoimmune glomerular diseases.

TScan-II: A genome-scale platform for the de novo identification of CD4+ T cell epitopes

CD4+ T cells play fundamental roles in orchestrating immune responses and tissue homeostasis. However, our inability to associate peptide human leukocyte antigen class-II (HLA-II) complexes with their cognate T cell receptors (TCRs) in an unbiased manner has hampered our understanding of CD4+ T cell function and role in pathologies. Here, we introduce TScan-II, a highly sensitive genome-scale CD4+ antigen discovery platform. This platform seamlessly integrates the endogenous HLA-II antigen-processing machinery in synthetic antigen-presenting cells and TCR signaling in T cells, enabling the simultaneous screening of multiple HLAs and TCRs. Leveraging genome-scale human, virome, and epitope mutagenesis libraries, TScan-II facilitates de novo antigen discovery and deep exploration of TCR specificity. We demonstrate TScan-II's potential for basic and translational research by identifying a non-canonical antigen for a cancer-reactive CD4+ T cell clone. Additionally, we identified two antigens for clonally expanded CD4+ T cells in Sjögren's disease, which bind distinct HLAs and are expressed in HLA-II-positive ductal cells within affected salivary glands.

Reactive Arthritis Resulting From Postoperative Complications of Third Molar Extraction: A Case Report

The role of bacterial infections as potential triggers for chronic rheumatic diseases is well-documented. Oral infections such as periodontitis may play a particularly important role in the development of autoimmune diseases, with the oral cavity serving as a reservoir for pathogenic bacteria. These bacteria may trigger dysregulatory immune responses through mechanisms like molecular mimicry, whereby bacterial peptides resemble self-peptides. Genetic factors may also predispose individuals to specific autoimmune diseases, most notably human leukocyte antigen B27 (HLA-B27) in the case of ankylosing spondylitis as well as other rheumatic diseases.

We present a case of a 23-year-old woman with reactive arthritis resulting from a postoperative infection. The patient presented with bilateral shoulder pain, decreased range of motion, worsening lower back pain, and mandibular pain at the site of a recent third molar extraction. Though initially diagnosed with rheumatoid arthritis, the patient experienced rapid and dramatic improvements following surgical treatment of the unresolved infection, demonstrating a causative or temporally related association between oral infections and chronic systemic autoimmune disease.

This case provides useful evidence regarding causal mechanisms for the connections between chronic autoimmune diseases and oral bacterial infection, illustrating how oral infection may serve as a causative factor for reactive arthritis. We suggest that this implicates bacteria normally present in oral microflora as a potential source of the antigens involved in triggering systemic inflammation, especially those already associated with other autoimmune diseases, such as Klebsiella pneumoniae in the case of ankylosing spondylitis. Based on prior publications linking self-peptides with homologies in such bacteria, we speculate on mechanisms underlying this connection, with particular attention to molecular mimicry. Clinicians should be aware of the close connection between certain rheumatic diseases (such as reactive arthritis) and bacterial infection, particularly of the oral cavity; such awareness should inform strategies for treatment and prevention of arthritic disease.

Walnut antigens can trigger autoantibody development in patients with pemphigus vulgaris through a "hit-and-run" mechanism

BACKGROUND

Environmental factors, as well as genetic predisposition, are known to be critical for the development of autoimmunity. However, the environmental agents that trigger autoimmune responses have remained elusive. One possible explanation is the "hit-and-run" mechanism in which the inciting antigens that initiate autoimmune responses are not present at the time of overt autoimmune disease.

OBJECTIVE

After our previous findings that some allergens can incite autoimmune responses, we investigated the potential role of environmental allergens in triggering autoantibody development in patients with an autoimmune skin disease, pemphigus vulgaris (PV).

METHODS

Revertant/germline mAbs (with mutations on variable regions of heavy and light chains reverted to germline forms) of 8 anti-desmoglein (Dsg) 3 pathogenic mAbs from patients with PV were tested for reactivity against a panel of possible allergens, including insects, pollens, epithelia, fungi, and food antigens.

RESULTS

All the PV germline mAbs were reactive to antigens from walnut, including the well-known allergen Jug r 2 and an uncharacterized 85-kDa protein component. Sera from patients with PV contained significantly greater levels of anti-Dsg3 autoantibodies than walnut-specific antibodies, suggesting that the autoreactive B-cell response in patients with PV might be initially triggered by walnut antigens but is subsequently driven by Dsg3.

CONCLUSION

Our findings suggest that walnut antigens/allergens can initiate autoantibody development in patients with PV through a "hit-and-run" mechanism. The revertant/germline mAb approach might provide a paradigm for the etiological study of other allergic and autoimmune diseases.

B cell epitope spreading: mechanisms and contribution to autoimmune diseases

While a variety of factors act to trigger or initiate autoimmune diseases, the process of epitope spreading is an important contributor in their development. Epitope spreading is a diversification of the epitopes recognized by the immune system. This process happens to both T and B cells, with this review focusing on B cells. Such spreading can progress among multiple epitopes on a single antigen, or from one antigenic molecule to another. Systemic lupus erythematosus, multiple sclerosis, pemphigus, bullous pemphigoid and other autoimmune diseases, are all influenced by intermolecular and intramolecular B cell epitope spreading. Endocytic processing, antigen presentation, and somatic hypermutation act as molecular mechanisms that assist in driving epitope spreading and broadening the immune response in autoimmune diseases. The purpose of this review is to summarize our current understanding of B cell epitope spreading with regard to autoimmunity, how it contributes during the progression of various autoimmune diseases, and treatment options available.

Human Endogenous Retroviruses (HERVs) and Autoimmune Rheumatic Disease: Is There a Link?

Autoimmune rheumatic diseases, such as RA and SLE, are caused by genetic, hormonal and environmental factors. Human Endogenous Retroviruses (HERVs) may be triggers of autoimmune rheumatic disease. HERVs are fossil viruses that began to be integrated into the human genome some 30-40 million years ago and now make up 8% of the genome. Evidence suggests HERVs may cause RA and SLE, among other rheumatic diseases. The key mechanisms by which HERVS are postulated to cause disease include molecular mimicry and immune dysregulation. Identification of HERVs in RA and SLE could lead to novel treatments for these chronic conditions. This review summarises the evidence for HERVs as contributors to autoimmune rheumatic disease and the clinical implications and mechanisms of pathogenesis are discussed.

Molecular mimicry: Basis for autoimmunity

Structural similarity between a viral protein and a self-component can trigger an autoimmune response, which is the basis of molecular mimicry. Alternatively an invading virus can induce an inflammatory response which in turn can initiate an attack by hitherto dormant T cells on a specific self-antigen, a phenomenon which is referred to as Bystander Activation. Several viruses share amino acid sequences with target self-proteins. A widely studied viral interaction is the structural mimicry of a small portion of coxsackie virus to a specific region of the enzyme glutamic acid decarboxylase (GAD) which is expressed by the β cells of the islet of Langerhans in the pancreas leading to the destruction of insulin producing cells and the onset of Type I insulin dependent diabetes mellitus (IDDM). Knowledge of specific epitopes in GAD susceptible to autoimmune attack can permit devising therapeutic strategies for the prevention and suppression of IDDM.

The prevalence and risk factors for coeliac disease among children and adolescents with type 1 diabetes mellitus

AIMS

Our aim was to determine in children with T1DM the prevalence of positive antibodies against tissue transglutaminase (anti-tTG IgA) as indices of coeliac disease (CD), as well as its clinical presentation, its determinants and its association with thyroid (anti-TG, anti-TPO) and pancreatic b-cell autoimmunity (anti-GAD).

METHODS

The study included 105 children and adolescents with T1DM, aged (mean±SD) 12.44±4.76 years, with a T1DM duration of 4.41±3.70 years.

RESULTS

Fifty of our patients (47.6%) were positive for anti-GAD, 9/105 (8.6%) for anti-tTG IgA and 21/105(20%) for anti-thyroid antibodies. The anti-tTG IgA (+) children, in comparison with the rest of the study population, were of younger age (9.31 vs. 12.74 years, p=0.038), shorter diabetes duration (2.16 vs. 4.62 years, p=0.056) and had mild growth impairment (height SDS: -0.55 vs. +0.20, p=0.055). Univariate logistic regression analysis revealed that the presence of anti-tTG IgA (+) was associated with younger age and shorter T1DM duration. Only 5/9 (55.6%) children with high titres of anti-tTG IgA developed mild gastrointestinal symptoms or growth retardation and had histological findings typical of CD.

CONCLUSIONS

The prevalence of anti-tTG IgA positivity among T1DM children was 8.6% and its occurrence was associated with younger age and short diabetes duration. Since CD presents in T1DM patients asymptomatically or with non-specific symptoms, periodic autoantibody screening is necessary for its early diagnosis.

Metabolic and genomic dissection of diabetes in the Cohen rat

We investigated the metabolic and genetic basis of diabetes in the Cohen Diabetic rat, a model of diet-induced diabetes, as a means to identify the molecular mechanisms involved. By altering individual components in the diabetogenic diet, we established that the dietary susceptibility that leads to the development of diabetes in this model is directly related to the high casein and low copper content in chow. The development of diabetes is accompanied by depletion of the acini from the exocrine pancreas and replacement with fat cells, while the appearance of the islets of Langerhans remains intact. With reversion back from diabetogenic to regular diet, the diabetic phenotype disappears but the histological changes in the exocrine pancreas prevail. Using positional cloning, we detected a major quantitative trait locus (QTL) on rat chromosome 4 with a chromosomal span of 4.9 cM, and two additional loci on chromosomes 7 and X. A screen for genes within that QTL in the rat and in the syntenic regions in mouse and man revealed only 23 candidate genes. Notable among these genes is Ica1, which has been causally associated with diabetes and bovine casein. We conclude that the development of diabetes in our model is dependent upon high casein and low copper in diet, that it is accompanied by histomorphological changes in the exocrine but not endocrine pancreas, that it is reversible, and that it is associated with a major QTL on chromosome 4 in which we detected Ica1, a high priority candidate gene.

CC chemokine receptor (CCR)-2 prevents arthritis development following infection by Mycobacterium avium

The host factors that influence autoimmune arthritides such as rheumatoid arthritis have not been fully elucidated. We previously found that genetic inactivation of CC chemokine receptor 2 (CCR2) in the arthritis-prone DBA/1j mouse strain significantly increases the susceptibility of this strain to autoimmune arthritis induced by immunization with collagen type II (CII) and complete Freund's adjuvant (CFA). Here, we show that following intradermal infection with Mycobacterium avium, a similar arthritis phenotype was detected in Ccr2-null mice in the DBA/1j, but not in the BALB/c background. The failure to develop arthritis in Ccr2-null BALB/c mice occurred in the face of high bacterial burdens and low interferon gamma (IFNgamma) production. By contrast, Ccr2-null DBA/1j mice had low bacterial burdens, produced normal amounts of IFNgamma, and had high titers of autoantibodies against CII. Thus, the Ccr2-null state in an arthritic-prone genetic background leads to increased arthritis susceptibility following infectious (M. avium) and noninfectious (CII/CFA) challenges. Because CCR2 serves as a negative regulator of murine arthritis, caution might need to be exercised while testing CCR2 blockers in human arthritis or other diseases. These findings also indicate that Ccr2-null DBA/1j mice might serve as a valuable model system to uncover the immunological determinants of arthritis and to test novel antiarthritic agents.

Associations between HLA-DQB1 high-risk alleles and type I diabetes do not depend on cytomegalovirus antibody status at onset: a case-parent study conducted in Chile

The purpose of the present study is to ascertain whether the associations between HLA-DQB1*0201 and DQB1*0302 alleles and childhood diabetes depend on the presence of antibodies to human cytomegalovirus (CMV). A study of incident type I diabetes cases and parents was conducted in Santiago, Chile. HLA-DQB1 polymorphisms were determined in 85 case-parent trios (255 subjects), while the detection of CMV was carried out only in the incident cases. As expected, HLA-DQB1 polymorphisms are strongly associated with type I diabetes, with crude odds ratios of 3.7 (95% confidence interval (CI) 1.8-7.7) for the DQB1*0201 allele and 10.3 (95% CI 5.0-21.4) for the DQB1*0302 allele. In the subset of families with CMV+ cases, the odds ratios were estimated as 3.7 (95% CI 1.6-8.6) for the DQB1*0201 allele and 11.1 (95% CI 4.8-25.8) for the DQB1*0302 allele. In families with patients who tested negative for CMV antibodies, the odds ratios were calculated as 3.5 (95% CI 0.7-16.8) for the DQB1*0201 allele, and 8.0 (95% CI 1.8-34.7) for the DQB1*0302 allele. There was no evidence of statistical interaction between CMV antibodies and the DQB1*0201 allele (P value = 0.9) or the DQB1*0302 allele (P value = 0.7). In conclusion, alleles DQB1*0302 and DQB1*0201 do not display distinct associations with type I diabetes depending on the presence of antibodies for CMV.