T-cell reactivity against streptococcal antigens in the periphery mirrors reactivity of heart-infiltrating T lymphocytes in rheumatic heart disease patients

HLA class II disease associations in southern Africa

Southern Africa harbors several population groups representing a diversity of gene pool origins. This provides a unique opportunity to study genetic disease predisposition in these populations against a common environmental background. Human leukocyte antigen (HLA) association studies of these populations could improve knowledge on inter-population variation and HLA-related disease susceptibility. The aim of this paper is to review HLA class II disease associations reported for southern African population groups, compare them with findings in other populations and identify those unique to southern Africa. A number of HLA class II disease associations appear to be unique to southern African populations. These include DRB1*14011 association with insulin-dependent diabetes mellitus susceptibility in the Xhosa and DRB1*10 and DQB1*0302 with rheumatoid arthritis susceptibility in the South African (SA) Indian and SA Coloreds, respectively. A noteworthy similarity in class II disease association was observed among southern African Caucasoid and their European parental populations. Unique HLA class II disease associations observed in southern Africa are consistent with the notion that unique environmental and natural selective factors have resulted in certain ethnic-specific HLA class II disease associations, while common HLA class II disease associations found across different populations support the notion that common diseases are caused by common, ancient alleles present in indigenous African populations.

Infections and autoimmune diseases

The high percentage of disease-discordant pairs of monozygotic twins demonstrates the central role of environmental factors in the etiology of autoimmune diseases. Efforts were first focussed on the search for triggering factors. The study of animal models has clearly shown that infections may trigger autoimmune diseases, as in the case of Coxsackie B4 virus in type I diabetes and the encephalomyocarditis virus in autoimmune myositis, two models in which viruses are thought to act by increasing immunogenicity of autoantigens secondary to local inflammation. The induction of a Guillain-Barré syndrome in rabbits after immunization with a peptide derived from Campylobacter jejuni is explained by mimicry between C. jejuni antigens and peripheral nerve axonal antigens. Other models involve chemical modification of autoantigens, as in the case of iodine-induced autoimmune thyroiditis. These mechanisms have so far only limited clinical counterparts (rheumatic fever, Guillain-Barré syndrome and drug-induced lupus or myasthenia gravis) but one may assume that unknown viruses may be at the origin of a number of chronic autoimmune diseases, such as type I diabetes and multiple sclerosis) as illustrated by the convergent data incriminating IFN-alpha in the pathophysiology of type I diabetes and systemic lupus erythematosus. Perhaps the difficulties met in identifying the etiologic viruses are due to the long lag time between the initial causal infection and onset of clinical disease. More surprisingly, infections may also protect from autoimmune diseases. Western countries are being confronted with a disturbing increase in the incidence of most immune disorders, including autoimmune and allergic diseases, inflammatory bowel diseases, and some lymphocyte malignancies. Converging epidemiological evidence indicates that this increase is linked to improvement of the socio-economic level of these countries, posing the question of the causal relationship and more precisely the nature of the link. Epidemiological and clinical data support the hygiene hypothesis according to which the decrease of infections observed over the last three decades is the main cause of the incessant increase in immune disorders. The hypothesis does not exclude an etiological role for specific pathogens in a given immune disorder as might notably be the case in inflammatory bowel diseases. Even in this setting, infections could still have a non-specific protective role. Independently of the need for confirmation by epidemiological prospective studies, the hygiene hypothesis still poses numerous questions concerning the nature of protective infectious agents, the timing of their involvement with regard to the natural history of immune diseases and, most importantly, the mechanisms of protection. Four orders of mechanisms are being explored. Antigenic competition is the first hypothesis (immune responses against pathogens compete with autoimmune and allergic responses). This is probably an important mechanism but its modalities are still elusive in spite of considerable experimental data. Its discussion in the context of homeostatic regulation of lymphocyte pools has shed new light on this hypothesis with possible competition for self MHC peptide recognition and interleukin-7. Another hypothesis deals with immunoregulation. Infectious agents stimulate a large variety of regulatory cells (Th2, CD25+, Tr1, NKT, ...) whose effects extend to other specificities than those which triggered their differentiation (bystander suppression). Infectious agents may also intervene through components which are not recognized as antigens but bind to specific receptors on cells of the immune system. Major attention has recently been drawn to Toll receptors (expressed on macrophages and possibly on regulatory T cells) and TIM proteins present on Th cells, which may express the function of the virus receptor (as in the case of the Hepatitis A virus and Tim-1). Experimental data will be presented to support each of these hypotheses. In any event, the final proof of principle will be derived from therapeutic trials where the immune disorders in question will be prevented or better cured by products derived from protective infectious agents. Numerous experimental data are already available in several models. Preliminary results have also been reported in atopic dermatitis using bacterial extracts and probiotics.

T cell mimicry and epitope specificity of cross-reactive T cell clones from rheumatic heart disease

Mimicry between streptococcal M protein and cardiac myosin is important in the pathogenesis of rheumatic heart disease. M protein-specific human T cell clones derived from rheumatic carditis were cross-reactive with human cardiac myosin, and laminin, a valve protein. Among the 11 CD4(+) and CD8(+) cross-reactive T cell clones, at least 6 different reactivity patterns were distinguished, suggesting different degrees of cross-reactivity and a very diverse T cell repertoire. The latter was confirmed by a heterogeneous Vbeta gene and CDR3 usage. HLA restriction and Th1 cytokine production in response to rM6 protein were preserved when the T cell clones were stimulated by human cardiac myosin or other alpha-helical proteins, such as tropomyosin and laminin. The cross-reactive human T cell clones proliferated to B2 and B3A, dominant peptide epitopes in the B repeat region of streptococcal M protein. In human cardiac myosin, epitopes were demonstrated in the S2 and light meromyosin regions. In our study, T cell mimicry was defined as recognition of structurally related Ags involved in disease and recognized by the same T cell. Mimicry in our study was related to alpha-helical coiled coil proteins which have a repetitive seven-aa residue periodicity that maintains alpha-helical structure and thus creates a high number of degenerate possibilities for recognition by T cells. The study of human T cell clones from rheumatic heart disease revealed potential sites of T cell mimicry between streptococcal M protein and human cardiac myosin and represents some of the most well-defined T cell mimicry in human autoimmune disease.

Infections and autoimmunity--good or bad?

The relationship between infections and autoimmunity is complex. Current evidence indicates that microbes can initiate, enhance, or, conversely, abrogate autoimmunity. In this paper, we will review experimental examples illustrating mechanisms involved in these three scenarios. Microbial infections can act as environmental triggers inducing or promoting autoimmunity resulting in clinical manifestations of autoimmune disease in genetically predisposed individuals. However, increasing evidence suggests the opposite outcome, which is the prevention or amelioration of autoimmune processes following microbial encounters. These latter observations support conceptually the "hygiene hypothesis," suggesting that cleaner living conditions will lead to enhanced incidence of autoimmune disorders, asthma, and allergies. Because proof of concept in humans is difficult to obtain, we will discuss relevant animal model data in context with likely or proven human associations. Knowledge of mechanisms that underlie either positive or negative effects of infections on autoimmunity will facilitate exploration of molecular details for prospective clinical studies in the future.

Acute rheumatic fever

Acute rheumatic fever (ARF) and its chronic sequela, rheumatic heart disease (RHD), have become rare in most affluent populations, but remain unchecked in developing countries and in some poor, mainly indigenous populations in wealthy countries. More than a century of research, mainly in North America and Europe, has improved our understanding of ARF and RHD. However, whether traditional views need to be updated in view of the epidemiological shift of the past 50 years is still to be established, and improved data from developing countries are needed. Doctors who work in populations with a high incidence of ARF are adapting existing diagnostic guidelines to increase their sensitivity. Group A streptococcal vaccines are still years away from being available and, even if the obstacles of serotype coverage and safety can be overcome, their cost could make them inaccessible to the populations that need them most. New approaches to primary prevention are needed given the limitations of primary prophylaxis as a population-based strategy. The most effective approach for control of ARF and RHD is secondary prophylaxis, which is best delivered as part of a coordinated control programme.

How an autoimmune reaction triggered by molecular mimicry between streptococcal M protein and cardiac tissue proteins leads to heart lesions in rheumatic heart disease

Molecular mimicry between microbial antigens and host tissue is suggested as a mechanism for post-infectious autoimmune disease. In the present work we describe the autoimmune reactions of two severe rheumatic heart disease (RHD) patients, through an analysis of heart-infiltrating T-cell repertoire, antigen recognition, and cytokine production induced by specific antigens. T-cell clones derived from oligoclonally expanded T cells in the heart cross-recognized M5 peptides, heart tissue-derived proteins, and myosin peptides. We show, using binding affinity assays, that an immunodominant streptococcal peptide (M5(81-96)) is capable of binding to the HLA-DR53 molecule. The same peptide was recognized by an infiltrating T-cell clone from a patient carrying HLA-DR15, DR7, and DR53 molecules. This suggests that this peptide is probably presented to T cells in the context of the HLA-DR53 molecule. Cross-reactive heart-infiltrating T cells activated by the M5 protein and its peptides and by heart tissue-derived proteins produced predominantly inflammatory cytokines. Interleukin (IL)-4 was produced in small amounts by mitral valve intralesional T-cell lines and clones. Altogether, these results suggest that mimicry between streptococcal antigens and heart-tissue proteins, combined with high inflammatory cytokine and low IL-4 production, leads to the development of autoimmune reactions and cardiac tissue damage in RHD patients.

Rheumatic heart disease: proinflammatory cytokines play a role in the progression and maintenance of valvular lesions

Heart lesions of rheumatic heart disease (RHD) patients contain T-cell clones that recognize heart proteins and streptococcal M peptides. To functionally characterize heart-infiltrating T lymphocytes, we evaluated their cytokine profile, both directly in situ and in T-cell lines derived from the heart (HIL). Interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, interleukin (IL)-4, and IL-10 expressions were characterized in 20 heart tissue infiltrates from 14 RHD patients by immunohistochemistry. IFN-gamma-, TNF-alpha-, and IL-10-positive cells were consistently predominant, whereas IL-4 was scarce in the valves. In agreement with these data, the in vitro experiments, in which 13 HILs derived from heart samples of eight patients were stimulated with M5 protein and the immunodominant M5 (81-96) peptide, IL-4 was detected in HIL derived from the atrium (three of six) but not from the valve (zero of seven). IFN-gamma and IL-10 production were detected in culture supernatants in 11 of 13 and 6 of 12 HILs, respectively. The predominant IFN-gamma and TNF-alpha expression in the heart suggests that Th1-type cytokines could mediate RHD. Unlike in reversible myocardium inflammation, the significantly lower IL-4 expression in the valvular tissue (P = 0.02) may contribute to the progression of the RHD leading to permanent valvular damage (relative risk, 4.3; odds ratio, 15.8). The lack of IL-4 in vitro production by valve-derived HIL also emphasizes the more severe tissue destruction in valves observed in RHD.

Rheumatic Fever: From Sore Throat to Autoimmune Heart Lesions

Molecular mimicry between streptococci and heart components has been proposed as the triggering factor leading to autoimmunity in rheumatic heart disease (RHD). In this review, we present data from cellular autoimmune responses, focusing on the interactions between HLA class II molecules, streptococcal peptides and heart tissue proteins and T-cell receptor (TCR) usage. HLA-DR7DR53 associated with DQ molecules seem to be related with the development of valvular lesions in severe RHD patients. DR7DR53 molecules were also involved in the recognition of an immunodominant M5 peptide in these patients. T cells infiltrating RHD hearts displayed several oligoclonal expansions. Intralesional T-cell clones presenting identical TCR-BVBJ AVAJ and -CDR3 sequences were able to recognize several antigens with little or low homology, showing an intramolecular degenerate pattern of antigen recognition. Peripheral blood mononuclear cells of rheumatic fever (RF) patients produced proinflammatory cytokines, and intralesional mononuclear cells from severe RHD patients produced predominantly Th1-type cytokines. These results illustrate the complex mechanisms leading to heart tissue damage in RF/RHD patients.

HLA class II associations with rheumatic heart disease among clinically homogeneous patients in children in Latvia

Genetic control of immune reactions has a major role in the development of rheumatic heart disease (RHD) and differs between patients with rheumatic fever (RF). Some authors think the risk of acquiring RHD is associated with the HLA class II DR and DQ loci, but other views exist, due to the various HLA-typing methods and ways of grouping cases. Our goal was to determine the relations between HLA class II alleles and risk of or protection from RF in patients with relatively homogeneous clinical manifestations. A total of 70 RF patients under the age of 18 years were surveyed in Latvia. HLA genotyping of DRB1*01 to DRB1*18 and DQB1*0201-202, *0301-305, *0401-402, *0501-504, and *0601-608 was performed using polymerase chain reaction sequence-specific primers. Data for a control group of 100 healthy individuals typed for HLA by the same method were available from the databank of the Immunology Institute of Latvia. Of the RF patients, 47 had RHD and 8 had Sydenham's chorea. We concluded that HLA class II DRB1*07-DQB1*0401-2 and DRB1*07-DQB1*0302 could be the risk alleles and HLA class II DRB1*06 and DQB1*0602-8, the protective ones. Patients with mitral valve regurgitation more often had DRB1*07 and DQB1*0401-2, and patients with multivalvular lesions more often had DRB1*07 and DQB1*0302. In Sydenham's chorea patients, the DQB1*0401-2 allele was more frequent. Genotyping control showed a high risk of RF and RHD in patients with DRB1*01-DQB1*0301-DRB1*07-DQB1*0302 and DRB1*15-DQB1*0302-DRB1*07-DQB1*0303.

In silico prediction of peptides binding to multiple HLA-DR molecules accurately identifies immunodominant epitopes from gp43 of Paracoccidioides brasiliensis frequently recognized in primary peripheral blood mononuclear cell responses from sensitized individuals

One of the major drawbacks limiting the use of synthetic peptide vaccines in genetically distinct populations is the fact that different epitopes are recognized by T cells from individuals displaying distinct major histocompatibility complex molecules. Immunization of mice with peptide (181-195) from the immunodominant 43 kDa glycoprotein of Paracoccidioides brasiliensis (gp43), the causative agent of Paracoccidioidomycosis (PCM), conferred protection against infectious challenge by the fungus. To identify immunodominant and potentially protective human T-cell epitopes in gp43, we used the TEPITOPE algorithm to select peptide sequences that would most likely bind multiple HLA-DR molecules and tested their recognition by T cells from sensitized individuals. The 5 most promiscuous peptides were selected from the gp43 sequence and the actual promiscuity of HLA binding was assessed by direct binding assays to 9 prevalent HLA-DR molecules. Synthetic peptides were tested in proliferation assays with peripheral blood mononuclear cells (PBMC) from PCM patients after chemotherapy and healthy controls. PBMC from 14 of 19 patients recognized at least one of the promiscuous peptides, whereas none of the healthy controls recognized the gp43 promiscuous peptides. Peptide gp43(180-194) was recognized by 53% of patients, whereas the other promiscuous gp43 peptides were recognized by 32% to 47% of patients. The frequency of peptide binding and peptide recognition correlated with the promiscuity of HLA-DR binding, as determined by TEPITOPE analysis. In silico prediction of promiscuous epitopes led to the identification of naturally immunodominant epitopes recognized by PBMC from a significant proportion of a genetically heterogeneous patient population exposed to P. brasiliensis. The combination of several such epitopes may increase the frequency of positive responses and allow the immunization of genetically distinct populations.

Induction of autoimmune valvulitis in Lewis rats following immunization with peptides from the conserved region of group A streptococcal M protein

Rheumatic heart disease (RHD) is considered to be an autoimmune disorder mediated by group A streptococcal (GAS) M protein-specific T cells and antibodies that cross-react with cardiac antigens and epitopes of the GAS M protein. In this study, Lewis rats were immunized with a pool of overlapping peptides spanning the conserved region of the GAS M protein in Complete Freund's Adjuvant, followed by immunization with Bordetella pertussis. Controls received adjuvants alone. Spleen-derived lymphocytes from rats immunized with the conserved region peptides proliferated in response to the immunogen and to cardiac myosin. Moreover, histological examination of cardiac tissue from rats immunized with conserved region peptides revealed the presence of inflammatory lesions in both the myocardium and valve tissue indicating a role for GAS M protein-specific autoreactive T cells in the development of cardiac lesions. This study may support the use of the rat model of autoimmune valvulitis to investigate the immunopathogenesis of RHD and possible preventive strategies.

A lipid core peptide construct containing a conserved region determinant of the group A streptococcal M protein elicits heterologous opsonic antibodies

The study reported here investigated the immunogenicity and protective potential of a lipid core peptide (LCP) construct containing a conserved region determinant of M protein, defined as peptide J8. Parenteral immunization of mice with LCP-J8 led to the induction of high-titer serum immunoglobulin G J8-specific antibodies when the construct was coadministered with complete Freund's adjuvant (CFA) or administered alone. LCP-J8 in CFA had significantly enhanced immunogenicity compared with the monomeric peptide J8 given in CFA. Moreover, LCP-J8/CFA and LCP-J8 antisera opsonized four different group A streptococcal (GAS) strains, and the antisera did not cross-react with human heart tissue proteins. These data indicate the potential of an LCP-based M protein conserved region GAS vaccine in the induction of broadly protective immune responses in the absence of a conventional adjuvant.

Rheumatic Fever

Rheumatic fever is an immunologically mediated inflammatory disease, that occurs as a delayed sequel to group A streptococcal throat infection, in genetically susceptible individuals. Chronic rheumatic heart disease remains an important public health problem in developing countries. Aetiopathogenesis and guidelines for the diagnosis, prevention and treatment of acute rheumatic fever are reviewed.