Structural basis of molecular mimicry

Potential clinical implications of molecular mimicry-induced autoimmunity

BACKGROUND

Molecular mimicry is hypothesized to be a mechanism by which autoimmune diseases are triggered. It refers to sequence or structural homology between foreign antigens and self-antigens, which can activate cross-reactive lymphocytes that attack host tissues. Elucidating the role of molecular mimicry in human autoimmunity could have important clinical implications.

OBJECTIVE

To review evidence for the role of molecular mimicry in major autoimmune diseases and discuss potential clinical implications.

METHODS

Comprehensive literature review of clinical trials, observational studies, animal models, and immunology studies on molecular mimicry in multiple sclerosis, type 1 diabetes, rheumatoid arthritis, lupus, Guillain-Barre syndrome, autoimmune myocarditis, and primary biliary cirrhosis published from 2000-2023.

RESULTS

Substantial indirect evidence supports molecular mimicry as a contributor to loss of self-tolerance in several autoimmune conditions. Proposed microbial triggers include Epstein-Barr virus, coxsackievirus, Campylobacter jejuni, and bacterial commensals. Key mechanisms involve cross-reactive T cells and autoantibodies induced by epitope homology between microbial and self-antigens. Perpetuation of autoimmunity involves epitope spreading, inflammatory mediators, and genetic factors.

CONCLUSIONS

Molecular mimicry plausibly explains initial stages of autoimmune pathogenesis induced by infection or microbiota disturbances. Understanding mimicry antigens and pathways could enable improved prediction, monitoring, and antigen-specific immunotherapy for autoimmune disorders. However, definitive proof of causation in humans remains limited. Further research should focus on establishing clinical evidence and utility.

TRIM5 Promotes Systemic Lupus Erythematosus Through CD4(+) T Cells and Macrophage

Purpose

Systemic lupus erythematosus (SLE) is a typical autoimmune disease characterized by the involvement of multiple organs and the production of antinuclear antibodies. This study aimed to investigate the molecular mechanism of SLE.

Patients and Methods

We retrieved genome-wide gene expression levels from five public datasets with relatively large sample sizes from the Gene Expression Omnibus (GEO), and we compared the expression profiles of peripheral blood mononuclear cells (PBMCs) from SLE patients and healthy controls (HCs). The expression of seven target genes in PBMCs from 25 cases and 3 HCs was further validated by reverse-transcription quantitative PCR (RT‒qPCR). Flow cytometry was used for verifying the proportion of naive CD4(+) T cells and M2 macrophages in PBMCs from 5 cases and 4 HCs.

Results

We found 14 genes (TRIM5, FAM8A1, SHFL, LHFPL2, PARP14, IFIT5, PARP12, DDX60, IRF7, IF144, OAS1, OAS3, RHBDF2, and RSAD2) that were differentially expressed among all five datasets. The heterogeneity test under the fixed effect model showed no obvious heterogeneity of TRIM5, FAM8A1, and SHFL across different populations. TRIM5 was positively correlated with the remaining 13 genes. By separating patient samples into TRIM5-high and TRIM5-low groups, we found that up-regulated genes in the TRIM5-high group were mainly enriched in virus-related pathways. Immune cell proportion analysis and flow cytometry revealed that naive CD4(+) T cells were significantly decreased while M2 macrophages were increased in the SLE group. TRIM5 expression levels were negatively correlated with naive CD4(+) T cells but positively correlated with M2 macrophages.

Conclusion

Our data indicated that TRIM5 might be a key factor that modulates SLE etiology, possibly through naive CD4(+) T cells and M2 macrophages.

Visiting Molecular Mimicry Once More: Pathogenicity, Virulence, and Autoimmunity

The concept of molecular mimicry describes situations in which antigen sharing between parasites and hosts could benefit pathogen evasion from host immune responses. However, antigen sharing can generate host responses to parasite-derived self-like peptides, triggering autoimmunity. Since its conception, molecular mimicry and the consequent potential cross-reactivity following infections have been repeatedly described in humans, raising increasing interest among immunologists. Here, we reviewed this concept focusing on the challenge of maintaining host immune tolerance to self-components in parasitic diseases. We focused on the studies that used genomics and bioinformatics to estimate the extent of antigen sharing between proteomes of different organisms. In addition, we comparatively analyzed human and murine proteomes for peptide sharing with proteomes of pathogenic and non-pathogenic organisms. We conclude that, although the amount of antigenic sharing between hosts and both pathogenic and non-pathogenic parasites and bacteria is massive, the degree of this antigen sharing is not related to pathogenicity or virulence. In addition, because the development of autoimmunity in response to infections by microorganisms endowed with cross-reacting antigens is rare, we conclude that molecular mimicry by itself is not a sufficient factor to disrupt intact self-tolerance mechanisms.

Epstein-Barr virus, interleukin-10 and multiple sclerosis: A ménage à trois

Multiple Sclerosis (MS) is an autoimmune disease that is characterized by inflammation and demyelination of nerve cells. There is strong evidence that Epstein-Barr virus (EBV), a human herpesvirus infecting B cells, greatly increases the risk of subsequent MS. Intriguingly, EBV not only induces human interleukin-10 but also encodes a homologue of this molecule, which is a key anti-inflammatory cytokine of the immune system. Although EBV-encoded IL-10 (ebvIL-10) has a high amino acid identity with its cellular counterpart (cIL-10), it shows more restricted and partially weaker functionality. We propose that both EBV-induced cIL-10 and ebvIL-10 act in a temporally and functionally coordinated manner helping the pathogen to establish latency in B cells and, at the same time, to balance the function of antiviral T cells. As a result, the EBV load persisting in the immune system is kept at a constant but individually different level (set point). During this immunological tug of war between virus and host, however, MS can be induced as collateral damage if the set point is too high. Here, we discuss a possible role of ebvIL-10 and EBV-induced cIL-10 in EBV-driven pathogenesis of MS.

The simple emergence of complex molecular function

At odds with a traditional view of molecular evolution that seeks a descent-with-modification relationship between functional sequences, new functions can emerge de novo with relative ease. At early times of molecular evolution, random polymers could have sufficed for the appearance of incipient chemical activity, while the cellular environment harbours a myriad of proto-functional molecules. The emergence of function is facilitated by several mechanisms intrinsic to molecular organization, such as redundant mapping of sequences into structures, phenotypic plasticity, modularity or cooperative associations between genomic sequences. It is the availability of niches in the molecular ecology that filters new potentially functional proposals. New phenotypes and subsequent levels of molecular complexity could be attained through combinatorial explorations of currently available molecular variants. Natural selection does the rest. This article is part of the theme issue 'Emergent phenomena in complex physical and socio-technical systems: from cells to societies'.

Synthetic Peptides with Inadvertent Chemical Modifications Can Activate Potentially Autoreactive T Cells

The human CD8+ T cell clone 6C5 has previously been shown to recognize the tert-butyl-modified Bax161-170 peptide LLSY(3-tBu)FGTPT presented by HLA-A*02:01. This nonnatural epitope was likely created as a by-product of fluorenylmethoxycarbonyl protecting group peptide synthesis and bound poorly to HLA-A*02:01. In this study, we used a systematic approach to identify and characterize natural ligands for the 6C5 TCR. Functional analyses revealed that 6C5 T cells only recognized the LLSYFGTPT peptide when tBu was added to the tyrosine residue and did not recognize the LLSYFGTPT peptide modified with larger (di-tBu) or smaller chemical groups (Me). Combinatorial peptide library screening further showed that 6C5 T cells recognized a series of self-derived peptides with dissimilar amino acid sequences to LLSY(3-tBu)FGTPT. Structural studies of LLSY(3-tBu)FGTPT and two other activating nonamers (IIGWMWIPV and LLGWVFAQV) in complex with HLA-A*02:01 demonstrated similar overall peptide conformations and highlighted the importance of the position (P) 4 residue for T cell recognition, particularly the capacity of the bulky amino acid tryptophan to substitute for the tBu-modified tyrosine residue in conjunction with other changes at P5 and P6. Collectively, these results indicated that chemical modifications directly altered the immunogenicity of a synthetic peptide via molecular mimicry, leading to the inadvertent activation of a T cell clone with unexpected and potentially autoreactive specificities.

Experimental Antiglomerular Basement Membrane GN Induced by a Peptide from Actinomyces

BACKGROUND

Antiglomerular basement membrane (anti-GBM) disease is associated with HLA-DRB1*1501 (the major predisposing genetic factor in the disease), with α3_127-148 as a nephritogenic T and B cell epitope. Although the cause of disease remains unclear, the association of infections with anti-GBM disease has been long suspected.

METHODS

To investigate whether microbes might activate autoreactive T and B lymphocytes via molecular mimicry in anti-GBM disease, we used bioinformatic tools, including BLAST, SYFPEITHI, and ABCpred, for peptide searching and epitope prediction. We used sera from patients with anti-GBM disease to assess peptides recognized by antibodies, and immunized WKY rats and a humanized mouse model (HLA-DR15 transgenic mice) with each of the peptide candidates to assess pathogenicity.

RESULTS

On the basis of the critical motif, the bioinformatic approach identified 36 microbial peptides that mimic human α3_127-148. Circulating antibodies in sera from patients with anti-GBM recognized nine of them. One peptide, B7, derived from Actinomyces species, induced proteinuria, linear IgG deposition on the GBM, and crescent formation when injected into WKY rats. The antibodies to B7 also targeted human and rat α3_127-148. B7 induced T cell activation from human α3_127-148-immunized rats. T cell responses to B7 were detected in rats immunized by Actinomyces lysate proteins or recombinant proteins. We confirmed B7's pathogenicity in HLA-DR15 transgenic mice that developed kidney injury similar to that observed in α3_135-145-immunized mice.

CONCLUSIONS

Sera from patients with anti-GBM disease recognized microbial peptides identified through a bioinformatic approach, and a peptide from Actinomyces induced experimental anti-GBM GN by T and B cell crossreactivity. These studies demonstrate that anti-GBM disease may be initiated by immunization with a microbial peptide.

Sphingolipids in Obesity and Correlated Co-Morbidities: The Contribution of Gender, Age and Environment

This paper reviews our present knowledge on the contribution of ceramide (Cer), sphingomyelin (SM), dihydroceramide (DhCer) and sphingosine-1-phosphate (S1P) in obesity and related co-morbidities. Specifically, in this paper, we address the role of acyl chain composition in bodily fluids for monitoring obesity in males and females, in aging persons and in situations of environmental hypoxia adaptation. After a brief introduction on sphingolipid synthesis and compartmentalization, the node of detection methods has been critically revised as the node of the use of animal models. The latter do not recapitulate the human condition, making it difficult to compare levels of sphingolipids found in animal tissues and human bodily fluids, and thus, to find definitive conclusions. In human subjects, the search for putative biomarkers has to be performed on easily accessible material, such as serum. The serum “sphingolipidome” profile indicates that attention should be focused on specific acyl chains associated with obesity, per se, since total Cer and SM levels coupled with dyslipidemia and vitamin D deficiency can be confounding factors. Furthermore, exposure to hypoxia indicates a relationship between dyslipidemia, obesity, oxygen level and aerobic/anaerobic metabolism, thus, opening new research avenues in the role of sphingolipids.

Molecular mimicry, genetic homology, and gene sharing proteomic "molecular fingerprints" using an EBV (Epstein-Barr virus)-derived microarray as a potential diagnostic method in autoimmune disease

EBV (Epstein-Barr Virus) and other human DNA viruses are associated with autoimmune syndromes in epidemiologic studies. In this work, immunoglobulin G response to EBV-encoded proteins which share regions with human immune response proteins from the human host including ZEBRA (BZLF-1 encoded protein), BALF-2 recombinase expressed primarily during the viral lytic replication cycle, and EBNA-1 (Epstein-Barr Virus Nuclear Antigen) expressed during the viral latency cycle respectively were characterized using a laser-printed micro-array ( PEPperprint.com ). IgG response to conserved "A/T hooks" in EBV-encoded proteins such as EBNA-1 and the BALF-2 recombinase related to host DNA-binding proteins including RAG-1 recombinase and histones, and EBV-encoded virokines such as the IL-10 homologue BCRF-1 suggest further directions for clinical research. The author suggests that proteomic "molecular fingerprints" of the immune response to viral proteins shared with human immune response genes are potentially useful in early diagnosis and monitoring of autoantibody production and response to therapy in EBV-related autoimmune syndromes.

Acellular Fish Skin Grafts and Pig Urinary Bladder Matrix Assessed in the Collagen-Induced Arthritis Mouse Model

It is vital that cellular- and tissue-based products (CTPs) used for wound treatment do not provoke autoimmunity. In this study, the immunogenic response to extracts of 2 CTPs of piscine and porcine origin was assessed in the collagen-induced arthritis model. Male DBA/1J mice were divided into 4 groups, each composed of 7 to 9 animals. Each animal was injected with one of following to assess their immune responses: (1) bovine type II collagen (100 µg) in Freund's adjuvant, (2) extract of piscine skin (100 µg) in Freund's adjuvant, (3) extract of porcine urinary bladder matrix (100 µg) in Freund's adjuvant, or (4) Freund's adjuvant alone (control) at the beginning of the experiment and 3 weeks later. Clinical signs of arthritis were assessed from week 5 onwards, and anti-type II and anti-type I collagen antibody immunoglobulin G (IgG) serum levels were measured before injections and 8 weeks after exposure using enzyme-linked immunosorbent assays. Only the mice exposed to bovine type II collagen developed clinical arthritis accompanied by very high anti-type II collagen IgG serum levels. Anti-type II collagen IgG serum levels were also detected in the porcine group but were undetectable in the piscine skin and control groups after 8 weeks. There were no significant differences in anti-type I collagen IgG serum levels among the groups. The results showed that piscine skin did not provoke systemic autoimmunity against type II collagens in DBA/1J mice.

Is there an association between pemphigus and hepatitis viruses? A population-based large-scale study

The association between pemphigus and hepatitis viruses has not been investigated sufficiently and remains unclear. Our objective was to assess the association between pemphigus and chronic hepatitis B (HBV) and hepatitis C (HCV) infections using a large-scale real-life computerized database. This study was conducted as a cross-sectional study utilizing the database of Clalit Health Services. The proportion of chronic HBV and HCV infections was compared between patients diagnosed with pemphigus and age-, sex-, and ethnicity-matched controls. Univariate analysis was performed using chi-square and Student's t test, and multivariate analysis was performed using a logistic regression model. A total of 1985 pemphigus patients and 9874 controls were enrolled in the study. The prevalence of HBV chronic infection in patients with pemphigus was significantly higher than in control subjects (1.2 vs. 0.6%, respectively, p = 0.008). The prevalence rate of HCV carrier state was comparable between pemphigus patients and control subjects (1.1 vs. 1.0, respectively, p = 0.732). A multivariate analysis revealed a significant association between pemphigus and HBV with a multivariate odds ratio (OR) of 1.9 [95% confidence interval (CI), 1.2-3.90], whereas no association between pemphigus and HCV was identified (OR 1.1, 95% CI, 0.7-1.7). In conclusion, patients with pemphigus have a greater proportion of chronic HBV but not HCV infection relative to matched controls.

Lateralized exanthem mimicking figurate inflammatory dermatosis of infancy after methimazole therapy

We reported a case of an 11-year-old girl admitted to our hospital for goiter, tachycardia, sweating, and visible and palpable thyroid. Thyroid function tests revealed a low thyrotropin level (<0.004 mIU/L) and elevated free thyroxine level (3.4 ng/ dL) diagnosed with Graves' disease and treated with methimazole. This anti-thyroid drug is recommended as first-line treatment in children with Graves' disease because it produces minor adverse effects with respect to propylthiouracil. She developed a lateralized exanthem mimicking figurate inflammatory dermatosis of infancy after methimazole therapy. The symptoms resolved after discontinuation of methimazole and treatment with an antihistamine and a corticosteroid. Furthermore, the treatment was changed to propylthiouracil without any adverse effects. According to current literature this is the first case of cutaneous figurate erythema related to methimazole, different from other well-known reactions such as skin eruption or urticaria.

A Dormant Microbial Component in the Development of Preeclampsia

Preeclampsia (PE) is a complex, multisystem disorder that remains a leading cause of morbidity and mortality in pregnancy. Four main classes of dysregulation accompany PE and are widely considered to contribute to its severity. These are abnormal trophoblast invasion of the placenta, anti-angiogenic responses, oxidative stress, and inflammation. What is lacking, however, is an explanation of how these themselves are caused. We here develop the unifying idea, and the considerable evidence for it, that the originating cause of PE (and of the four classes of dysregulation) is, in fact, microbial infection, that most such microbes are dormant and hence resist detection by conventional (replication-dependent) microbiology, and that by occasional resuscitation and growth it is they that are responsible for all the observable sequelae, including the continuing, chronic inflammation. In particular, bacterial products such as lipopolysaccharide (LPS), also known as endotoxin, are well known as highly inflammagenic and stimulate an innate (and possibly trained) immune response that exacerbates the inflammation further. The known need of microbes for free iron can explain the iron dysregulation that accompanies PE. We describe the main routes of infection (gut, oral, and urinary tract infection) and the regularly observed presence of microbes in placental and other tissues in PE. Every known proteomic biomarker of "preeclampsia" that we assessed has, in fact, also been shown to be raised in response to infection. An infectious component to PE fulfills the Bradford Hill criteria for ascribing a disease to an environmental cause and suggests a number of treatments, some of which have, in fact, been shown to be successful. PE was classically referred to as endotoxemia or toxemia of pregnancy, and it is ironic that it seems that LPS and other microbial endotoxins really are involved. Overall, the recognition of an infectious component in the etiology of PE mirrors that for ulcers and other diseases that were previously considered to lack one.

Gangliosides as a potential new class of stem cell markers: the case of GD1a in human bone marrow mesenchymal stem cells

Owing to their exposure on the cell surface and the possibility of being directly recognized with specific antibodies, glycosphingolipids have aroused great interest in the field of stem cell biology. In the search for specific markers of the differentiation of human bone marrow mesenchymal stem cells (hBMSCs) toward osteoblasts, we studied their glycosphingolipid pattern, with particular attention to gangliosides. After lipid extraction and fractionation, gangliosides, metabolically (3)H-labeled in the sphingosine moiety, were separated by high-performance TLC and chemically characterized by MALDI MS. Upon induction of osteogenic differentiation, a 3-fold increase of ganglioside GD1a was observed. Therefore, the hypothesis of GD1a involvement in hBMSCs commitment toward the osteogenic phenotype was tested by comparison of the osteogenic propensity of GD1a-highly expressing versus GD1a-low expressing hBMSCs and direct addition of GD1a in the differentiation medium. It was found that either the high expression of GD1a in hBMSCs or the addition of GD1a in the differentiation medium favored osteogenesis, providing a remarkable increase of alkaline phosphatase. It was also observed that ganglioside GD2, although detectable in hBMSCs by immunohistochemistry with an anti-GD2 antibody, could not be recognized by chemical analysis, likely reflecting a case, not uncommon, of molecular mimicry.

The microbiome and probiotics in childhood

Infants, from the moment of birth, are colonized by large numbers of microbes. This colonization continues throughout childhood and from preliminary studies seems to be a highly dynamic process, even during the usual physiologic state we refer to as health. In this context, the persistence of bacterial and fungal species in and on the human body likely confers various benefits to the host. One specific approach to modulate such beneficial effects is the administration of probiotics, also known as beneficial microbes. Herein, we outline the highest level evidence in regard to the evolution of the microbiome during childhood and its manipulation by probiotics for genitourinary, enteric, and allergic and atopic disorders. Thus, probiotic approaches are promising alternatives and adjuvants to traditional vaccines and antibiotics. This may usher in a new age in which vaccine and antibiotic side effects and antibiotic resistance are minimal issues in the setting of maintaining children's health and prevention of disease.

Structural and dynamic control of T-cell receptor specificity, cross-reactivity, and binding mechanism

Over the past two decades, structural biology has shown how T-cell receptors engage peptide/major histocompatibility complex (MHC) complexes and provided insight into the mechanisms underlying antigen specificity and cross-reactivity. Here we review and contextualize our contributions, which have emphasized the influence of structural changes and molecular flexibility. A repeated observation is the presence of conformational melding, in which the T-cell receptor (TCR), peptide, and in some cases, MHC protein cooperatively adjust in order for recognition to proceed. The structural changes reflect the intrinsic dynamics of the unligated proteins. Characterization of the dynamics of unligated TCR shows how binding loop motion can influence TCR cross-reactivity as well as specificity towards peptide and MHC. Examination of peptide dynamics indicates not only peptide-specific variation but also a peptide dependence to MHC flexibility. This latter point emphasizes that the TCR engages a composite peptide/MHC surface and that physically the receptor makes little distinction between the peptide and MHC. Much additional evidence for this can be found within the database of available structures, including our observations of a peptide dependence to the TCR binding mode and structural compensations for altered interatomic interactions, in which lost TCR-peptide interactions are replaced with TCR-MHC interactions. The lack of a hard-coded physical distinction between peptide and MHC has implications not only for specificity and cross-reactivity but also the mechanisms underlying MHC restriction as well as attempts to modulate and control TCR recognition.

[Immunology for understanding the pathogenesis of multiple sclerosis]

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS) and the pathogenesis leading to demyelination includes 3 major processes. The first step is establishment of autoimmunity to CNS myelin components, with molecular mimicry between a portion of the infectious agents and that of myelin, which is an important feature. The second step is entry of immune cells into the CNS via the blood-brain barrier (BBB). Activated T cells can easily cross the BBB using surface LFA-1 and VLA-4 as ligands to ICAM-1 and VCAM-1, respectively, which are expressed on endothelial cells in the CNS. As the third step, immune reactions occur within the CNS when activated T cells encounter specific antigens presented by microglia. Of the helper T cells re-stimulated by autoantigens, Th1 cells producing interferon-γ and Th17 cells secreting interleukin-17 play major roles in propagating inflammation, while Th2 cells producing IL-4, and regulatory T cells secreting IL-10 and TGF-β suppress pathological processes. Final demyelination is rendered either by macrophages recruited from the bloodstream across the BBB, or by TNF-α and nitric oxide, which are secreted by Th1 cells and macrophages, and toxic to CNS myelin.

[Report from the Committee for Advanced Therapies (CAT). Pitfalls on the way from concept to medical treatment with advanced therapy medicinal products]

Advanced therapy medicinal products (ATMP) are highly innovative and complex medicines. They comprise gene therapy medicinal products, somatic cell therapy medicinal products, and tissue-engineered products (TEP). With the European Regulation on ATMP that came into force in 2008, a consolidated regulatory framework was created, where the Committee for Advanced Therapies (CAT) at the European Medicines Agency (EMA) plays a central role. This article discusses pitfalls and challenges that the CAT has experienced in its discussions of various procedures. Often ATMPs are developed by small and medium-sized enterprises (SME) which also face nonscientific challenges. The CAT wishes to meet these challenges on a scientific and regulatory level during its 2010-2015 work program.

Conformational melding permits a conserved binding geometry in TCR recognition of foreign and self molecular mimics

Molecular mimicry between foreign and self Ags is a mechanism of TCR cross-reactivity and is thought to contribute to the development of autoimmunity. The αβ TCR A6 recognizes the foreign Ag Tax from the human T cell leukemia virus-1 when presented by the class I MHC HLA-A2. In a possible link with the autoimmune disease human T cell leukemia virus-1-associated myelopathy/tropical spastic paraparesis, A6 also recognizes a self peptide from the neuronal protein HuD in the context of HLA-A2. We found in our study that the complexes of the HuD and Tax epitopes with HLA-A2 are close but imperfect structural mimics and that in contrast with other recent structures of TCRs with self Ags, A6 engages the HuD Ag with the same traditional binding mode used to engage Tax. Although peptide and MHC conformational changes are needed for recognition of HuD but not Tax and the difference of a single hydroxyl triggers an altered TCR loop conformation, TCR affinity toward HuD is still within the range believed to result in negative selection. Probing further, we found that the HuD-HLA-A2 complex is only weakly stable. Overall, these findings help clarify how molecular mimicry can drive self/nonself cross-reactivity and illustrate how low peptide-MHC stability can permit the survival of T cells expressing self-reactive TCRs that nonetheless bind with a traditional binding mode.

First-in-human clinical trials with vaccines--what regulators want

Several factors should be taken into account when it comes to the first exposure of humans to a novel vaccine.

Postinfectious immunodeficiency and autoimmunity: pathogenic and clinical values and implications

Autoimmunity is still a mystery of clinical immunology and medicine as a whole. The etiology and pathogenesis of autoimmune disorders remain unclear and, thus, are assessed as a balance between hereditary predisposition, triggering factors and the appearance of autoantibodies and/or self-reactive T cells. Among the immunological armamentarium, molecular mimicry, based on self-reactive T- and B-cell activation by cross-reactive epitopes of infectious agents, is of special value. Hypotheses regarding the possible involvement of molecular mimicry in the development of postinfectious autoimmunity are currently very intriguing. They provide new approaches for identifying etiological agents that are associated with postinfectious autoimmunity, paired microbial- and tissue-linked epitopes targeted for autoimmune reaction determination, postinfectious autoimmunity pathogenesis recognition and specific prevention, and therapy for autoimmune disorder development.

Mycobacterium avium subsp. paratuberculosis as a trigger of type-1 diabetes: destination Sardinia, or beyond?

Type 1 diabetes mellitus (T1DM) is a multifactorial autoimmune disease in which the insulin producing beta cell population is destroyed by the infiltrated T lymphocytes. Even though the exact cause of T1DM is yet to be ascertained, varying degree of genetic susceptibility and environmental factors have been linked to the disease progress and outcome. Mycobacterium avium subsp. paratuberculosis (MAP) is an obligate zoonotic pathogen that causes chronic infection of intestines in ruminants, the Johne's disease. MAP that can even survive pasteurization and chlorination has also been implicated to cause similar type of enteritis in humans called Crohn's disease. With the increasing recognition of the link between MAP and Crohn's disease, it has been postulated that MAP is an occult antigen which besides Crohn's could as well be thought to trigger T1DM. Epitope homologies between mycobacterial proteins (Hsp 65) and pancreatic glutamic acid decarboxylase (GAD 65) and infant nutrition studies implicate MAP as one of the triggers for T1DM. PCR and ELISA analyses in diabetic patients from Sardinia suggest that MAP acts as a possible trigger for T1DM. Systematic mechanistic insights are needed to prove this link. Unfortunately, no easy animal model(s) or in-vitro systems are available to decipher the complex immunological network that is triggered in MAP infection leading to T1DM.

Humoral immunity in tuberculin skin test anergy and its role in high-risk persons exposed to active tuberculosis

The most common test to identify latent tuberculosis is the tuberculin skin test that detects T cell responses of delayed type hypersensitivity type IV. Since it produces false negative reactions in active tuberculosis or in high-risk persons exposed to tuberculosis patients as shown in this report, we studied antibody profiles to explain the anergy of such responses in high-risk individuals without active infection. Our results showed that humoral immunity against tuberculin, regardless of the result of the tuberculin skin test is important for protection from active tuberculosis and that the presence of high antibody titers is a more reliable indicator of infection latency suggesting that latency can be based on the levels of antibodies together with in vitro proliferation of peripheral blood mononuclear cells in the presence of the purified protein derivative. Importantly, anti-tuberculin IgG antibody levels mediate the anergy described herein, which could also prevent reactivation of disease in high-risk individuals with high antibody titers. Such anti-tuberculin IgG antibodies were also found associated with blocking and/or stimulation of in vitro cultures of PBMC with tuberculin. In this regard, future studies need to establish if immune responses to Mycobacterium tuberculosis can generate a broad spectrum of reactions either toward Th1 responses favoring stimulation by cytokines or by antibodies and those toward diminished responses by Th2 cytokines or blocking by antibodies; possibly involving mechanisms of antibody dependent protection from Mtb by different subclasses of IgG.

Presence of autoimmune antibody in chikungunya infection

Chikungunya infection has recently re-emerged as an important arthropod-borne disease in Thailand. Recently, Southern Thailand was identified as a potentially endemic area for the chikungunya virus. Here, we report a case of severe musculoskeletal complication, presenting with muscle weakness and swelling of the limbs. During the investigation to exclude autoimmune muscular inflammation, high titers of antinuclear antibody were detected. This is the report of autoimmunity detection associated with an arbovirus infection. The symptoms can mimic autoimmune polymyositis disease, and the condition requires close monitoring before deciding to embark upon prolonged specific treatment with immunomodulators.

Lipid autoreactivity in multiple sclerosis

Lipids comprise over 70% of the myelin sheath but have been largely underinvestigated as autoantigens in multiple sclerosis (MS). This paper cites evidence for the involvement of lipid autoreactivity in MS and details how self lipid cross-reactivity may also contribute to the development of type 1 diabetes and autoimmune thyroid disorders (both of which have been associated with MS). A further analysis of myelin chemistry suggests several mechanisms by which infection may contribute to etiology and trigger lipid autoreactivity via molecular mimicry. This analysis may aid the development of new therapies for autoimmune diseases.

Hepatitis B virus (HBV) and autoimmune disease

The etiology and pathogenesis of autoimmune diseases have long been an enigmatic subject that have involved genetic and environmental factors. Recent intriguing data has contributed to the mechanisms involved, including the relationship of infectious agents and loss of tolerance. This loss of tolerance is illustrated by the data on the immune response to Hepatitis B virus such as the molecular mimicry between HBV antigens and self proteins, the generation of immune complexes between HBV antigens and antibodies, and apoptosis/tissue damage resulting in the exposure of intracellular antigens to the immune system. In this paper, we review the current database related to HBV infection and a variety of autoimmune conditions, including autoimmune hepatitis, systemic lupus erythematosus, aplastic anemia, antiphospholipid syndrome, polyarteritis nodosa, rheumatoid arthritis, type 1 diabetes, multiple sclerosis, thyroid disease and uveitis.

Pathophysiology and clinical spectrum of infections in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an inflammatory and multisystemic autoimmune disorder characterized by an uncontrolled autoreactivity of B and T lymphocytes leading to the production of autoantibodies against self-directed antigens and tissue destruction. Environmental factors, such as infections, which are an important cause of morbidity and mortality, are potential triggers of the disease. This article discusses bacterial, viral, and opportunistic microorganism infections in SLE, and the role of immunosuppressive therapy and immunodeficiencies in the disease.

Lymphocyte Subpopulations, Oxidative Burst and Apoptosis in Peripheral Blood Cells of Patients with Multiple Sclerosis–Effect of Interferon-β

At present, the most efficient therapeutical treatment of multiple sclerosis (MS) is achieved by IFN-beta. However, its in vivo effects remain incompletely understood. If applied parenterally, the hydrophobic IFN-beta acts primarily on blood cells with probable selectivity for functionally different lymphocyte subpopulations, monocytes and granulocytes. We have investigated the expression of the activation marker interleukin-2 receptor-alpha (CD25) on CD3+ T cells, CD19+ B cells, foetal-type gamma(delta)+CD3+ T cells and foetal-type CD5+CD19+ B cells of the peripheral blood. In addition, the oxidative burst activity and apoptosis have been determined in mononuclear and polymorphonuclear blood cells, respectively. The study accompanied a phase III trial with IFN-beta1b (BETAFERON, Schering). Two groups of MS patients with relapsing-remitting course of the disease have been investigated at 8 time points (days 0, 5, 15, 31, 60, 90, 180 and 270 after starting therapy): (1) verum group (n = 8) with application of 8 Mill. units IFN-beta1 b every other day, and (2) placebo group (n = 4) with application of placebo for 3 months and therapy as in (1) from day 90 onward. The main results were: (1) Activated T cells decreased until day 180 in the verum group and return thereafter to pre-treatment values, whereas in the placebo group the values remained relatively stable over the whole observation period. (2) Activated B cells increased between days 90 and 270 in both groups, i.e. after verum application in both groups. (3) Foetal-type B cells were more activated than total B and T cells with increase over time in both groups. (4) Foetal-type T cells exerted relatively stable intra-individual levels with generally low CD25 expression, but punctual CD25 peaks in both groups. (5) The spontaneous oxidative burst was higher in lymphocytes, more variable in monocytes and faster increasing in granulocytes in the verum group than in the placebo group. (6) Apoptosis of mononuclear cells and granulocytes showed similar variations in the verum and placebo groups with the exception of a selective increase over time of the proportion of granulocytes undergoing induced apoptosis in the verum group. It is concluded that IFN-beta has the following main effects on the immune system of MS patients: (1) the T cell immunity is systemically and reversibly suppressed, (2) the foetal-type lymphocytes, which are responsible for the first line of defence of infections, are stimulated in the long range, (3) the oxidative burst activity is increased in lymphocytes and granulocytes and instable in monocytes, and (4) the inducibility of apoptosis in granulocytes is increased. Re-examination of the altered blood cell parameters after long-term IFN-beta therapy is warranted.

Multiple sclerosis - a response-to-damage model

According to a widely supported but unproven concept, the autoimmune mechanisms that drive neuroinflammation in multiple sclerosis (MS) are triggered by virus infection. However, a direct viral trigger of MS has not been identified. MS models in non-human primates suggest that lifelong asymptomatic infection with certain herpesviruses (e.g. cytomegalovirus) creates a repertoire of potentially autoreactive memory T cells. When these are exposed to antigens released after central nervous system injury as a consequence of an unknown pathogenic event, they are reactivated and induce autoimmune neurological disease. This response-to-damage of antiviral memory cells can take place years after the initiating infection. Consequently, elucidating the anti-herpesvirus T-cell repertoire might provide new targets for preventive diagnosis and therapy.

The human microbiome and probiotics: implications for pediatrics

The “human super-organism” refers to the human body and the massive numbers of microbes which dwell within us and on the skin surface. Despite the large numbers of microbes co-existing within the human body, humans including infants and children achieve a physiologic state of equilibrium known as health in the context of this microbial world. These key concepts suggest that many individual members of the human microbiome, including bacterial and fungal species, confer different benefits on the human host. Probiotics, or beneficial microbes, may modulate immune responses, provide key nutrients, or suppress the proliferation and virulence of infectious agents. The human microbiome is in fact dynamic and often in flux, which may be indicative of the continuous interplay among commensal microbes, pathogens, and the human host. In this article we review the state-of-the-art regarding probiotics applications to prevent or treat diseases of the pediatric gastrointestinal and genitourinary systems. Additionally, probiotics may regulate local and systemic immunity, thereby reducing allergic disease severity and susceptibilities of infants and children to allergies and atopic diseases. In summary, beneficial microbes offer promising alternatives for new strategies in therapeutic microbiology with implications for different subspecialties within pediatrics. Instead of simply trying to counteract microbes with vaccines and antibiotics, a new field of medical microbiology is emerging that strives to translate human microbiome research into new probiotics strategies for promotion of health and prevention of disease in children.

Viral infection can induce the production of autoantibodies

PURPOSE OF REVIEW

To review the current literature and summarize the main principles found between viral infections and the subsequent production of autoantibodies.

RECENT FINDINGS

We concentrate on recent findings involving three viral agents, one of which is Epstein-Barr virus, which has been associated with many autoimmune diseases and is classically considered to induce systemic lupus erythematosus. As we will discuss, this occurs through molecular mimicry between Epstein-Barr virus nuclear antigen 1 and lupus-specific antigens such as Ro, La or dsDNA, through induction of Toll-like receptor hypersensitivity by Epstein-Barr virus latent membrane protein 2A or by creating immortal B and T cells by loss of apoptosis. Hepatitis B virus was found to share amino acid sequences with different autoantigens. Tissue damage and the release of intracellular components is just another example of the autoantibody production caused by this virus. Cytomegalovirus has often been controversially associated with several autoimmune diseases and, although is the least understood viral infection of the three, appears to be somewhat suspicious.

SUMMARY

Understanding the infectious origin of autoimmune diseases is important as we aim to identify high-risk patients and disrupt this process with vaccines or other medications, ultimately delaying or even preventing the evolution of autoimmune diseases.

Epstein Barr Virus and Cytomegalovirus in Autoimmune Diseases: Are They Truly Notorious? A Preliminary Report

To date, it is believed that the origin of autoimmune diseases is one of a multifactorial background. A genetic predisposition, an immune system malfunction or even backfire, hormonal regulation, and environmental factors all play important roles in the pathogenesis of autoimmune diseases. Among these environmental factors, the role of infection is known to be a major one. Epstein-Barr virus (EBV) and cytomegalovirus (CMV) are considered to be notorious as they are consistently associated with multiple autoimmune diseases. A cohort of 1595 serum samples, of 23 different autoimmune disease groups, was screened for evidence of prior infection with EBV and CMV. All samples were screened for antibodies against EBV nuclear antigen-1 (IgG), EBV viral capsid antigen (IgG and IgM), EBV early antigen (IgG), EBV heterophile antibody, and CMV (IgG and IgM) antibodies using Bio-Rad's BioPlex 2200. A new association is proposed between EBV and polymyositis, as results show a significant increase in titers of various EBV target analytes when compared with healthy controls. Our results also support prior information suggesting the association between EBV and multiple autoimmune diseases, including SLE, antiphospholipid syndrome, rheumatoid arthritis, multiple sclerosis, pemphigus vulgaris, giant cell arthritis, Wegener's granulomatosis, and polyarteritis nodosa (PAN). Elevated CMV IgG titers were observed in sera of SLE patients. Our data support the theory that EBV is notoriously associated with many autoimmune diseases. CMV appears to be associated to autoimmune diseases as well, yet establishing this theory requires further investigation.

Chemical validation of molecular mimicry: interaction of cholera toxin with Campylobacter lipooligosaccharides

It is generally believed that molecular mimicry between bacterial lipooligosaccharide (LOS) and nerve glycolipids may play an important pathogenic role in immune-mediated peripheral neuropathy. One of the putative infectious agents is Campylobacter jejuni (C. jejuni). To elucidate the structural basis for the molecular mimicry, we investigated the structure of the lipooligosaccharide (LOS) fraction of C. jejuni, strain HS19, and found that it includes at least two components, characterized as fast-and slow-moving bands (LF and LS) by thin-layer chromatography as revealed by cholera toxin B subunit (Ctxb) overlay. Structural analysis of the oligosaccharide portion of LS established that it had the following structure: Gal-GalNAc-(NeuAc)Gal-Hep-(Glc;PO(3)H)Hep-Kdo. The GM1-like epitope was validated by a terminal tetrasaccharide unit within this structure. On the other hand, analysis of LF revealed an entirely different structure: 1, 4'-bisphosphoryl glucosamine disaccharide N, N'-acylated by 3-(2-hydroxytetracosanoyloxy)octadecanoic acid at 2- and 2'-positions, which is consistent with that of lipid A. No GM1-like epitope was observed in LF. Both LS and LF interacted with Ctxb as demonstrated by TLC-overlay and sucrose density gradient centrifugation. Surprisingly, LF does not have the basic GM1 structure for interacting with Ctxb. Instead, the affinity of LF to Ctxb required that one or both of the phosphate groups be present in the glucosamine disaccharide residue because after alkaline phosphatase treatment the dephosphorylated LF was unable to bind to Ctxb. We conclude that LS is likely the component contributing to GM1-mimicry in autoimmune peripheral neuropathy and that the role of LF is not clear but may be associated with the initial activation of autoreactive T cells.

Why much of the pathophysiology of preeclampsia-eclampsia must be of an autoimmune nature

Preeclampsia-eclampsia (PE-E) is a poorly understood condition of human pregnancy, which can affect multiple organs and is a leading cause of maternal deaths worldwide. The etiology and pathophysiology remain enigmas, however, which hampers progress in prevention, diagnosis, and treatment of this condition. PE-E is characterized by many features typically seen in autoimmune diseases, or in association with autoimmune reactions. Although this does not mean that PE-E should be considered an autoimmune condition, it does suggest that abnormal autoimmune processes play an important part in the clinical presentation of PE-E. In that regard, PE-E mimics autoimmune responses also observed in situations of allograft rejection and graft-versus-host disease (GVHD). Indeed, PE-E shares many other clinical and laboratory characteristics with allograft rejection and GVHD. Recognizing PE-E as a clinical condition that is characterized by autoimmune abnormalities may facilitate earlier and more specific diagnosis, along with preventive and more specific therapies for women at risk.

Autoantibodies that recognize functional domains of hnRNPA1 implicate molecular mimicry in the pathogenesis of neurological disease

As a model for molecular mimicry in neurological disease, we study people infected with human T-lymphotropic virus type 1 (HTLV-1) who develop HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP), an immune-mediated disease of the central nervous system (CNS). In HAM/TSP, data suggests molecular mimicry is the result of cross-reactive antibodies between HTLV-1-tax and heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), a protein over-expressed in human CNS neurons. The hnRNP A1 epitope recognized by autoantibodies was unknown. In this study, we hypothesized that antibodies purified from HAM/TSP patients would react with functionally significant domains of hnRNP A1. Western blotting of functionally significant deletion mutants and overlapping fusion proteins using HAM/TSP IgG revealed two core epitopes within the C-terminal region of hnRNP A1. The first (aminoacids 191-SSQRGRSGSGNF-202), overlapped the RGG domain and the second (aminoacids 293-GQYFAKPRNQGG-304), with the M9 shuttling sequence, two functionally important regions of hnRNP A1. Monoclonal antibodies to HTLV-1-tax also reacted with the epitopes. These data fulfill an important criterion of molecular mimicry, namely that mimicking epitopes are not random, but include biologically significant regions of target proteins. This suggests an important role for the cross-reactive immune response between HTLV-1 and hnRNP A1 in the pathogenesis of immune-mediated neurological diseases via molecular mimicry.

Molecular basis for the binding polyspecificity of an anti-cholera toxin peptide 3 monoclonal antibody

The onset of autoimmune diseases is proposed to involve binding promiscuity of antibodies (Abs) and T-cells, an often reported yet poorly understood phenomenon. Here, we attempt to approach two questions: first, is binding promiscuity a general feature of monoclonal antibodies (mAbs) and second, what is the molecular basis for polyspecificity? To this end, the anti-cholera toxin peptide 3 (CTP3) mAb TE33 was investigated for polyspecific binding properties. Screening of phage display libraries identified two epitope-unrelated peptides that specifically bound TE33 with affinities similar to or 100-fold higher than the wild-type epitope. Substitutional analyses revealed distinct key residue patterns recognized by the antibody suggesting a unique binding mode for each peptide. A database query with one of the consensus motifs and a subsequent binding study uncovered 45 peptides (derived from heterologous proteins) that bound TE33. To better understand the structural basis of the observed polyspecificity we modeled the new cyclic epitope in complex with TE33. The interactions between this peptide and TE33 suggested by our model are substantially different from the interactions observed in the X-ray structure of the wild-type epitope complex. However, the overall binding conformation of the peptides is similar. Together, our results support the theory of a general polyspecific potential of mAbs.

Trypanosoma cruzi-induced molecular mimicry and Chagas' disease

Chagas' disease, caused by Trypanosoma cruzi, has been considered a paradigm of infection-induced autoimmune disease. Thus, the scarcity of parasites in the chronic phase of the disease contrasts with the severe cardiac pathology observed in approximately 30% of chronic patients and suggested a role for autoimmunity as the origin of the pathology. Antigen-specific and antigen-non-specific mechanisms have been described by which T. cruzi infection might activate T and B cells, leading to autoimmunity. Among the first mechanisms, molecular mimicry has been claimed as the most important mechanism leading to autoimmunity and pathology in the chronic phase of this disease. In this regard, various T. cruzi antigens, such as B13, cruzipain and Cha, cross-react with host antigens at the B or T cell level and their role in pathogenesis has been widely studied. Immunization with those antigens and/or passive transfer of autoreactive T lymphocytes in mice lead to clinical disturbances similar to those found in Chagas' disease patients. On the other hand, the parasite is becoming increasingly detected in chronically infected hosts and may also be the cause of pathology either directly or through parasite-specific mediated inflammatory responses. Thus, the issue of autoimmunity versus parasite persistence as the cause of Chagas' disease pathology is hotly debated among many researchers in the field. We critically review here the evidence in favor of and against autoimmunity through molecular mimicry as responsible for Chagas' disease pathology from clinical, pathological and immunological perspectives.

Women and autoimmune diseases

Autoimmune diseases affect approximately 8% of the population, 78% of whom are women. The reasons for the high prevalence in women are unknown, but circumstantial evidence links autoimmune diseases with preceding infections. Animal models of autoimmune diseases have shown that infections can induce autoimmune disease. For example, coxsackievirus B3 (CB3) infection of susceptible mice results in inflammation of the heart (myocarditis) that resembles myocarditis in humans. The same disease can be induced by injecting mice with heart proteins mixed with adjuvant(s), which indicates that an active infection is not necessary for the development of autoimmune disease. We have found that CB3 triggers autoimmune disease in susceptible mice by stimulating elevated levels of proinflammatory cytokines from mast cells during the innate immune response. Sex hormones may further amplify this hyperimmune response to infection in susceptible persons, which leads to an increased prevalence of autoimmune diseases in women.

A structural basis for CD8+ T cell-dependent recognition of non-homologous peptide ligands: implications for molecular mimicry in autoreactivity

Molecular mimicry of self-epitopes by viral antigens is one possible pathogenic mechanism underlying induction of autoimmunity. A self-epitope, mDBM, derived from mouse dopamine beta-mono-oxygenase (KALYDYAPI) sharing 44% sequence identity with the lymphocytic choriomeningitis virus-derived immunodominant epitope gp33 (KAVYNFATC/M), has previously been identified as a cross-reactive self-ligand, presentation of which results in autoimmunity. A rat peptide homologue, rDBM (KALYNYAPI, 56% identity to gp33), which displayed similar properties to mDBM, has also been identified. We herein report the crystal structure of H-2Db.rDBM and a comparison with the crystal structures of the cross-reactive H-2Db.gp33 and non-cross-reactive H-2Db.gp33 (V3L) escape variant (KALYNFATM, 88% identity to gp33). Despite the large sequence disparity, rDBM and gp33 peptides are presented in nearly identical manners by H-2Db, with a striking juxtaposition of the central sections of both peptides from residues p3 to p7. The structural similarity provides H-2Db in complex with either a virus-derived or a dopamine beta-mono-oxygenase-derived peptide with a shared antigenic identity that conserves the positioning of the heavy chain and peptide residues that interact with the T cell receptor (TCR). This stands in contrast to the structure of H-2Db.gp33 (V3L), in which a single conserved mutation, also present in rDBM, induces large movements of both the peptide backbone and the side chains that interact with the TCR. The TCR-interacting surfaces of the H-2Db.rDBM and H-2Db.gp33 major histocompatibility complexes are very similar with regard to shape, topology, and charge distribution, providing a structural basis for CD8 T cell activation by molecular mimicry and potential subsequent development of autoreactivity.

Limited in vivo reactivity of polyclonal effector cytotoxic T cells towards altered peptide ligands

T cell responses are regulated by the affinity/avidity of the T cell receptor for the MHC/peptide complex, available costimulation and duration of antigenic stimulation. Altered peptide ligands (APLs) are usually recognized with a reduced affinity/avidity by the T cell receptor and are often able to only partially activate T cells in vitro or may even function as antagonists. Here we assessed the ability of APLs derived from peptide p33 of lymphocytic choriomeningitis virus (LCMV) to mediate lysis of target cells in vivo, confer anti-viral protection and cause auto-immune disease. In general, in vitro cross-reactivity between APLs was rather limited, and even strongly cross-reactive cytotoxic T lymphocytes were only able to mediate moderate anti-viral protection. Partial protection was observed for infection with LCMV or low doses of recombinant vaccinia virus, while no reduced viral titers could be seen upon infection with high dose of vaccinia virus. In a transgenic mouse model expressing LCMV glycoprotein in the islets of the pancreas, APLs induced a transient insulitis but failed to induce autoimmune diabetes. Thus, effector functions induced by even highly homologous APLs are rather limited in vivo.