Autoimmunity versus tolerance: analysis using transgenic mice

On the basis of our extensive studies on collagen induced arthritis in HLA class II transgenic mice, we proposed a hypothesis to explain role of shared epitope in rheumatoid arthritis (RA) association. According to our hypothesis, complementation between both DQ and DR molecules is required for susceptibility or protection from disease. While certain DQ alleles predispose individuals to RA, DRB1 molecule can modulate disease by shaping T-cell repertoire in the thymus by providing self-peptides and presented by DQ molecules. Using A beta o.DQ8 transgenic mice, we tested ability of peptides derived from HV3 of DR molecules, implicated in RA positively or negatively, to activate T cells. While the peptides derived from RA susceptible DR molecule were poor binders and poor in activating T cells, the peptides derived from RA resistant DR molecules were high affinity binders and efficient T-cell activators. Our experiments suggest that high affinity DR peptides could induce tolerance to autoimmunity while the low affinity peptides could be permissive to autoimmunity. Using peptide from DRB1*0402 molecule, known to be associated with resistance to RA, prior to induction of collagen induced arthritis prevents the onset of disease. Thus, self-peptides derived from HLA molecules could potentially generate tolerance or autoimmunity depending on their binding affinity with HLA molecules.     

Transgenic mouse models of rheumatoid arthritis

Summary: A combined analysis of data available m the literature has demonstrated that the strongest association in rheumatoid arthritis (RA) is with DR genes rather than DQ or DP genes. Functional and structural data of RA-associated DR molecules suggest that selective binding of peptides is the molecular basis for this association. The establishment of functional transgenic mice expressing RA-associated HLA class II molecules has proven to be useful in the delineation of the role of these molecules in immune responses possibly related to RA and in the development of humanized models for this disease. Such humanized mice develop arthritis upon immunization with type II collagen (CII), which shows similarities with RA, Interestingly, the immunodominant T-cell determinant in CII is derived from positions 261–273, which overlap with a previously identified CII T-cell epitope restricted by the mouse Ai molecule, which is associated with collagen-induced arthritis. Studies in collagen transgenic mice have shown that recognition of this peptide may lead either to T-cell tolerance or to an arthritogenic response. It is therefore proposed that the T-cell recognition of the CII peptide bound by DR molecules is one of the molecular interactions of critical importance in the development of RA and accordingly also an important target for prevention and treatment of this disease.     

Role of HLA class II genes in susceptibility/resistance to inflammatory arthritis: studies with humanized mice

Summary: Predisposition to develop rheumatoid arthritis (RA) has been associated with certain human leukocyte antigen (HLA) class II molecules, although the mechanism is still unknown. Various experimental animal models of inflammatory arthritis have been studied to address the role of major histocompatibility complex (MHC) genes in pathogenesis. We have generated transgenic mice expressing HLA class II molecules (DR and DQ) lacking complete endogenous class II molecules to study the interactions involved between class II molecules (DQ and DR) and to define the immunologic mechanisms in inflammatory arthritis. The HLA transgene can positively select CD4⁺ T cells expressing various Vβ T-cell receptors, and a peripheral tolerance is maintained to transgenic HLA molecules. The expression of HLA molecules on various cells in these mice is similar to that known in humans. In this review, we describe collagen-induced arthritis as a model for human inflammatory arthritis using these transgenic mice. The transgenic mice carrying RA-susceptible haplotype develop gender-biased inflammatory arthritis with clinical and histopathological similarities to RA. Our studies show that polymorphism of HLA class II genes determine the predisposition to rheumatoid/inflammatory arthritis and the epistatic interactions between HLA-DQ and HLA-DR molecules dictate the severity, progression, and modulation of the disease.     

DR4Dw4/DR53 molecules contain a peptide from the autoantigen calreticulin

Abstract: Rheumatoid arthritis (RA) occurs more frequently in HLA-DR4⁺ individuals than in those who do not express this MHC class II molecule. Although the role of this genetic factor in the immunopathology of this autoimmune disease is unclear, the association of RA with HLA-DR4 may indicate that DR4 molecules present autoantigen(s) to T cells. Here we report the analysis of naturally processed peptides, eluted from a mixture of HLA-DR4Dw4 (DRB1*0401) and DR53 (DRB4* 0101) molecules isolated from an RA patient-derived EBV-transformed B cell line. Several (size variants of) self-peptides originating from the autologous molecules HLA-A2, HLA-Cw9, HLA-B62, HLA-DR4Dw4 and HLA-DR53, were identified. We also found a sequence that has no homology to any protein in the SwissProt protein sequence databank, and a peptide identical to an internal fragment of the autoantigen calreticulin. The association of the identified peptides with cells expressing HLA-DR4Dw4/DR53 was confirmed by peptide binding analysis. In agreement with previously described peptide binding motifs for DR4Dw4, most peptides contained an aromatic residue (Phe, Tyr, Trp) at relative position i and a small hydroxyl-containing residue (Ser, Thr) at i+5. Our findings indicate that in RA patient-derived EBV-transformed B cells DR4Dw4/ DR53 molecules present a peptide from the autoantigen calreticulin. Interestingly, autoantibodies against calreticulin have been found in various rheumatic diseases, including rheumatoid arthritis. Thus, the analysis of HLA class II-bound peptides can lead to the identification of putative T helper epitopes, which might be involved in the immunopathology of autoimmune diseases.     

An HLA-DRB1*0402 derived peptide (HV3 65-79) prevents collagen-induced arthritis in HLA-DQ8 transgenic mice.

On the basis of our studies with HLA class II transgenic mice, we had proposed that complementation of HLA-DQ and HLA-DR alleles may determine both disease susceptibility and severity in rheumatoid arthritis (RA). According to our model, certain HLA-DQ alleles, such as HLA-DQ8, predispose individuals to RA, while a self-peptide derived from the third hypervariable region (HV3 65-79) of HLA-DR alleles, such as DRB 1*0402, can protect from disease if presented by the DQ molecule. To test this hypothesis, we examined the immunomodulatory effects of the DRB1*0402 derived peptide (HV3 65-79) on collagen-induced arthritis (CIA) in HLA-DQ8 mice. Co-immunization of the DRB 1*0402 peptide significantly reduced the severity of arthritis (mean score = 1.5+/-0.6 vs 5.2+/-1.4 in controls), whereas multiple doses of the peptide reduced the incidence of disease (3.5% vs 35-60% in controls). Subsequent analysis revealed that the DRB1*0402 peptide mediated protection may be due to the generation of a subset of regulatory cells, which down-regulate collagen-specific pro-inflammatory responses. These results provide additional insights towards understanding the role of MHC class II molecules in RA predisposition.     

To B or not to B: role of B cells in pathogenesis of arthritis in HLA transgenic mice

Population studies have shown that amongst all the genetic factors linked with autoimmune disease development, MHC class II genes are the most significant. Experimental autoimmune arthritis resembling human rheumatoid arthritis (RA) can be induced in susceptible strains of mice following immunization with type II collagen (CIA). We generated transgenic mice lacking endogenous class II molecules and expressing various HLA genes including RA-associated, HLA-DRB1*0401 and HLA-DQ8, and RA-resistant, DRB1*0402, genes. The HLA molecules in these mice are expressed on the cell surface and can positively select CD4+ T cells expressing various Vβ T cell receptors. Endogenous class II invariant chain is required for proper functioning of the class II transgene. Arthritis development in transgenic mice is CD4+ and B cells dependent. Studies in humanized mice showed that B cells are required as antigen presenting cells in addition to antibody producing cells for the development of CIA. The transgenic mice expressing *0401 and *0401/DQ8 genes developed sex-biased arthritis with predominantly females being affected, similar to that of human RA. Further, the transgenic mice produced autoantibodies like rheumatoid factor and anti-cyclic antibodies. Antigen presentation by B cells leads to a sex-specific immune response in DRB1*0401 mice suggesting a role of B cells and HLA-DR in rendering susceptibility to develop arthritis in females.     

B cells as effectors and regulators of sex-biased arthritis

B cells have been implicated both with pathogenic as well as protective capabilities in induction and regulation of autoimmune diseases. Rheumatoid arthritis (RA) is an autoimmune disease that occurs more often in women than men. A significant role of B cells as antibody producing and antigen-presenting cells has been demonstrated in RA. Predisposition to RA is associated with the presence of certain HLA class II alleles that share sequences with DRB1*0401. To determine the role of HLA genes and B cells in vivo, we have generated transgenic mice carrying HLA genes, DRB1*0401 and DQ8, known to be associated with susceptibility to RA. Humanized mice can be induced to develop arthritis that mimics human disease in clinical, histopathological and sex bias. Effect of hormones on immune cells and their function has been described in humans and mice and has been suggested to be the major reason for female bias of autoimmune diseases. An immune response to an antigen requires presentation by HLA molecules thus suggesting a critical role of MHC in combination with sex hormones in susceptibility to develop rheumatoid arthritis. Based on our observations, we hypothesize that modulation of B cells by estrogen, presentation of modified antigens by DR4 and production of antigen-specific B cell modulating cytokines leads to autoreactivity in females. These data suggest that considering patient's sex may be crucial in selecting the optimal treatment strategy. Humanized mice expressing RA susceptible and resistant haplotype provide a means to investigate mechanism sex-bias of arthritis and future strategies for therapy.     

Humanized transgenic mice expressing HLA DR4-DQ3 haplotype: reconstitution of phenotype and HLA-restricted T-cell responses

Many autoimmune conditions have close genetic linkages to particular human histocompatibility leukocyte antigen (HLA) class II genes. With the aim of establishing a murine model of autoimmune disease, we have generated an HLA DR4-DQ3 haplotype transgenic (Tg) mouse that expresses a 440-kb yeast artificial chromosome harbouring DRA, DRB1*040101, DRB4*010301, DQA1*030101, DQB1*0302 and all the internal regulatory segments. This Tg mouse line was crossed to human CD4 (hCD4) Tg mice and endogenous class II knockout mice (I-A(o/o) and I-E(o/o)) lines to generate a DR4-DQ3.hCD4.IAE(o/o) Tg line. The Tg DR and DQ molecules are expressed on the physiological cell types in these animals, i.e. on most B cells (>85%), dendritic cells (DCs) and macrophages but not on T cells, with levels of expression comparable with those of human B cells (where DR > DQ expression). The DR4/DQ3 transgenes fully reconstituted the CD4 T-cell compartment, in both the thymus and the periphery, and the analysis of the T-cell receptor repertoire in the Tg mice confirmed that these class II molecules were able to mediate thymic selection of a broad range of Vbeta families. HLA DR4- and DQ3-restricted T-cell responses were elicited following immunization with known T-cell determinants presented by these molecules. Furthermore, the DR4-DQ3-restricted CD4(+) T cells conferred protective antibody-mediated immunity against an otherwise lethal infection with Salmonella enterica var. typhimurium. These new DR4-DQ3 Tg mice should prove to be valuable tools for dissecting the importance of this class II haplotype in autoimmune disorders like rheumatoid arthritis.     

A Peptide-Binding Assay for the Disease-Associated HLA-DQ8 Molecule

The study of peptide binding to HLA class II molecules has mostly concentrated on DR molecules. Since many autoimmune diseases show a primary association to particular DQ molecules rather than DR molecules, it is also important to study the peptide-binding properties of DQ molecules. Here we report a biochemical peptide-binding assay for the type I diabetes-associated DQ8, i.e. DQ (α1*0301, β1*0302), molecule. Affinity-purified DQ8 molecules were tested in peptide-binding assays using a radiolabelled influenza haemagglutinin (Ha) peptide encompassing positions 255–271(Y) as an indicator peptide. The Ha 255–271(Y) peptide bound to DQ8 in a pH-dependent fashion showing optimal binding around pH 5. The association kinetics were relatively slow and the resulting complexes were heat labile. The specificity of peptide binding to DQ8 was investigated in competitive inhibition experiments with a panel of 43 peptides of different lengths and sequences. The DQ8 molecules showed a different pattern of peptide binding compared to a previously studied DQ2 molecule. Peptides derived from thyroid peroxidase, HLA-DQ(α1*0301), HLA-DQ(α1*0302), retinol receptor and p21ras were among the high-affinity binders, whereas peptides derived from myelin basic protein were among the low-affinity binders. The sequence of the high-affinity peptides conformed with a previously published peptide-binding motif of DQ8.     

Differences in self-peptide binding between T1D-related susceptible and protective DR4 subtypes

HLA-DR0401, 0403 and 0405 are associated with variable T1D susceptibilities when linked with a common HLA-DQ8 (DQA110301/DQB110302). It is unknown how the modest differences within the peptide binding regions of DR4 subtypes lead to distinct autoimmune risks. Since all Class II HLA molecules share the same intracellular compartments during biosynthesis, it is possible that DQ and DR compete with one another to bind and present antigenic peptides. As such, it is reasonable to hypothesize that a strong DR4 self-peptide binder down-modulates DQ8 epitope presentation more than a weak one. In this study, we first examined the binding of the peptides derived from two putative beta-cell autoantigens – GAD65 and insulin. Protective DR0403 bound similar number of self-peptides as susceptible DR0401 while highly susceptible DR0405 bound substantially less self-peptides than rest two molecules. Kinetic assays were used to further compare the stability of peptide:DR complexes formed between DR0401, 0403 and selected GAD65 peptides, which also bound DQ8. Two peptides with naturally processed DQ8 epitopes bound protective DR0403 with longer half-life and lower dissociation rate than susceptible DR0401, confirming DR0403 as a better peptide competitor than DR0401. The distinguishing peptide binding features of DR0401, DR0403, and DR0405 highlighted in this study help to explain the hierarchy of genetic associations between T1D and these DR4 subtypes. The enhanced peptide competition of DR0403 leads to a down-modulation of DQ8 epitope presentation, as compared to weak competitors such as DR0401 and DR0405, and therefore contributes to disease protection.     

Selection of Self-reactive Peptides Within Human Aggrecan by use of a HLA-DRB1*0401 Peptide Binding Motif

The pathogenesis of joint destruction in rheumatoid arthritis remains ill-defined. Joint destruction is thought to be the result of tissue damage mediated by T cells. The mere presence of articular cartilage appears responsible for sustaining chronic synovitis and thereby forwards a role for cartilage-responsive T cells in RA. Taking advantage of the positive DRB1*0401 association with RA susceptibility, we reasoned that T-cell recognition of autoantigens in RA would be restricted by DRB1*0401-encoded molecules. A DR4 (B1*0401) peptide binding motif was used for the identification of putative T-cell epitopes within human aggrecan, a candidate autoantigen. Thirteen peptides were synthesized and tested for binding DRB1*0401 or 0404-encoded molecules. Selected binders were tested for induction of pro-liferative responses in peripheral blood mononuclear cells from donors carrying the DR4 or DR1 specificity. Both healthy and RA donors responded to human aggrecan-derived peptides, thereby identifying these sequences as T-cell epitopes. Interestingly, responses to aggrecan-derived epitopes were significantly decreased in RA patients compared to controls. This was not due to an overall hyporesponsiveness of RA patients since responses to a recall antigen or mitogen did not differ from controls. The data suggest that in RA, aggrecan-specific T cells may exist in a different stage of activation or may have left the periphery to home to the joint.     

HLA class II association with rheumatoid arthritis: facts and interpretations

We have reviewed the literature on the association of HLA class II with rheumatoid arthritis (RA). Strong linkage disequilibrium among DQB1, DQA1 and DRB1 alleles makes it difficult to evaluate the individual contribution of each locus. Nonetheless, there is a strong case for the role of DQB1*03 and *04 combined with DQA1*03 in susceptibility to severe RA while DQB1*0501 combined with DQA1*0101 and *0104 weakly predisposes to a mild form of RA. However, it is also clear that DRB1*0401 has a particular role in predisposition to the most severe form of the disease while other DRB1 alleles might provide protection. We would like to propose that in RA, as in type I diabetes, both DQ and DR loci contribute to predisposition to the disease.     

B cells as effectors and regulators of sex-biased arthritis

B cells have been implicated both with pathogenic as well as protective capabilities in induction and regulation of autoimmune diseases. Rheumatoid arthritis (RA) is an autoimmune disease that occurs more often in women than men. A significant role of B cells as antibody producing and antigen-presenting cells has been demonstrated in RA. Predisposition to RA is associated with the presence of certain HLA class II alleles that share sequences with DRB1*0401. To determine the role of HLA genes and B cells in vivo, we have generated transgenic mice carrying HLA genes, DRB1*0401 and DQ8, known to be associated with susceptibility to RA. Humanized mice can be induced to develop arthritis that mimics human disease in clinical, histopathological and sex bias. Effect of hormones on immune cells and their function has been described in humans and mice and has been suggested to be the major reason for female bias of autoimmune diseases. An immune response to an antigen requires presentation by HLA molecules thus suggesting a critical role of MHC in combination with sex hormones in susceptibility to develop rheumatoid arthritis. Based on our observations, we hypothesize that modulation of B cells by estrogen, presentation of modified antigens by DR4 and production of antigen-specific B cell modulating cytokines leads to autoreactivity in females. These data suggest that considering patient's sex may be crucial in selecting the optimal treatment strategy. Humanized mice expressing RA susceptible and resistant haplotype provide a means to investigate mechanism sex-bias of arthritis and future strategies for therapy.     

The HLA-DQ7 and -DQ8 associations in DR4-positive rheumatoid arthritis patients A combined analysis of data available in the literature

Several different lines of evidence have demonstrated that inherited susceptibility to rheumatoid arthritis (RA) is associated with the DRB1 genes encoding the HLA-DR4 and HLA-DR1 molecules. A contrasting hypothesis has recently been proposed, suggesting that, in general, the DRB1 locus is associated with protection to RA and that the RA-associated DRB1 alleles are not responsible for the primary disease association but merely permissive for the susceptibility conferred by the HLA-DQ alleles with which they are in linkage disequilibrium. We have performed a critical review of the literature on the HLA association in RA with special emphasis on studies in which both an HLA-DR and -DQ association has been investigated. Our analyses provide strong evidence against the hypothesis that HLA-DQ molecules play a major role in the general susceptibility to RA. Thus, the strongest association in rheumatoid arthritis is with DRB1 genes rather than DQB1 genes.     

Immunodominant T‐cell epitopes of hnRNP‐A2 associated with disease activity in patients with rheumatoid arthritis

The heterogeneous nuclear ribonucleoprotein A2 (hnRNP‐A2) has been described as an important autoantigen in rheumatoid arthritis (RA) since it is targeted by autoantibodies, autoreactive T cells, and is aberrantly expressed in synovial cells in patients. To identify hnRNP‐A2‐specific T‐cell epitopes possibly associated with pathogenicity, we used an innovative approach. We first scanned 280 overlapping hnRNP‐A2 peptides for binding to the RA‐associated class II molecules HLA‐DR4 and HLA‐DR1, leading to a comprehensive selection of binders. The selected peptides were tested in IFN‐γ‐specific ELISPOT assay: PBMC from 18% of RA patients showed a significant IFN‐γ response to hnRNP‐A2 peptides, 15% to the overlapping sequences 117–133 and/or 120–133, whereas PBMC from healthy individuals tested negative. We measured proliferative responses to these two peptides in another cohort of patients with RA or osteoarthritis: positive responses were found in 28% of RA, but also in 11% of osteoarthritis patients and these responses could be blocked by anti‐MHC class II Ab. Remarkably, the presence of 117/120–133‐specific T cells was significantly associated with active disease in RA patients, and bone erosion appeared to be more common in T‐cell positive patients. These data suggest involvement of hnRNP‐A2 specific cellular autoimmune responses in RA pathogenesis.     

Analysis of the binding of gluten T-cell epitopes to various human leukocyte antigen class II molecules

Celiac disease is a prevalent disorder of the small intestine that is caused by an inflammatory reaction to dietary gluten in genetically susceptible individuals. More than 90% of patients express the HLA-DQ2 molecule, whereas DQ8 is carried by most of the remaining patients. DQ2- and DQ8-mediated presentation of gluten peptides to CD4+ T cells is a key event in the pathogenesis of the disease. The association of celiac disease with these human leukocyte antigen (HLA) molecules is explained by a preferential binding of gluten peptides to these HLA molecules, although the actual data on this in the literature are scarce. The objective of this study was to test this hypothesis. A panel of peptides representing DQ2-restricted gluten T-cell epitopes was tested for binding to various HLA class II molecules using various experimental approaches. The results demonstrate that the gluten T-cell epitopes mainly bind to the DQ2 molecule.     

Protection against severe disease is conferred by DERAA-bearing HLA-DRB1 alleles among HLA-DQ3 and HLA-DQ5 positive rheumatoid arthritis patients

Experimental studies in transgenic mice have suggested that HLA-DQ predisposes to rheumatoid arthritis (RA), but could also modulate disease severity by presenting peptides derived from self-DR molecules. In particular, a short amino acid sequence, (70)DERAA(74), in the third hypervariable region of HLA-DRB1 confers protection for the disease, while particular HLA-DQ [DQB1*0501/DQA1*01 (DQ5) and DQB1*03/DQA1*03 (DQ3)] molecules predispose to the disease. We have therefore analyzed the allelic distribution of HLA-DRB1, DQA1, and DQB1 and the presence of rheumatoid factor and nodules among 199 German RA patients and 196 healthy controls. Our results show that HLA-DQB1*03/DQA1*03 (or DRB1*04) predisposes to RA more than HLA-DQB1*0501/DQA1*01 (i.e., DRB1*01 and DRB1*10). Homozygosity for DQ3 confers the strongest genetic risk for RA (OR = 19.79 compared to OR = 10.05 for two doses of shared epitope (SE) positive HLA-DRB1 alleles). Furthermore, patients carrying both predisposing DQ and (70)DERAA(74)-positive HLA-DRB1 alleles are more often rheumatoid factor (RF) negative than patients carrying predisposing DQ alleles alone. Only one out of 14 patients (7%) with a protective combination (DQ3/(70)DERAA(74) and DQ5/(70)DERAA(74)) had rheumatoid nodules compared to 67 out of 144 patients (46.5%) with predisposing DQ alleles alone (OR = 0.12, 95% CI: 0.02-0.72, p = 0.004). These results demonstrate a protective role of (70)DERAA(74)-positive DRB1 alleles against disease severity among RA patients.     

Self-peptides that bind with low affinity to the diabetes-associated I-A(g7) molecule readily induce T cell tolerance in non-obese diabetic mice

Although non-obese diabetic (NOD) mice spontaneously develop T cell autoimmunity, it is not clear whether this phenomenon results from a defect in tolerance to self-Ag. Furthermore, as autoimmunity has been postulated to result from T cell responses directed toward self-peptides that bind with low affinity to NOD I-A(g7) MHC class II molecules, it is important to determine whether the expression of such peptides induces tolerance. We have constructed NOD transgenic (Tg) mice expressing the Leishmania antigen receptor for C kinase (LACK) Ag in either the thymus or pancreatic beta cells. We identified LACK peptides that were the targets of T cells in LACK-immunized NOD mice while binding to I-A(g7) with low affinity. While CD4(+) T cells from NOD mice secreted IFN-gamma, IL-4, IL-5 and IL-10 in response to LACK, those from LACK-expressing Tg mice secreted reduced levels of cytokines. Experiments using peptide/MHC multimers showed that LACK-expressing Tg mice exhibited self-reactive CD4(+) T cells with impaired proliferation capabilities. Hence, even self-peptides that bind to I-A(g7) with low affinity can induce tolerance in NOD mice. This result is important in light of the commonly held hypothesis that T cells reacting to peptides that bind to MHC with low affinity escape tolerance induction and cause autoimmunity.     

Discordant expression of HLA class II-associated co-chaperones and HLA-DRB alleles in cultured fibroblast-like synoviocytes

Human leukocyte antigen (HLA)-DR-positive synovial fibroblasts are frequently observed in rheumatoid arthritis (RA) and may be implicated in the autoimmune reaction because RA is associated with certain HLA-DRB1* alleles. The question of whether components of the class II antigen presentation pathway and specific DRB alleles are efficiently expressed by synovial fibroblasts is germane to this hypothesis. To address this, cultured fibroblast-like synoviocytes (cFLS) were analyzed for constitutive and interferon (IFN)-γ-induced expression of specific DRB alleles and class II-associated cochaperones. IFN-γ induction of invariant chain, DM, and DR molecules was observed in all cFLS, but expression of specific DR allotypes was variable. Interestingly, DM-modulated epitopes on RA-associated DR molecules were either absent or delayed, despite strong DM expression and a paucity of major histocompatibility complex/class II-associated invariant chain peptide complexes. Altered expression of specific peptide-dependent epitopes on RA-associated HLA-DR molecules suggests differences in antigen presentation by cFLS, which may have implications for the immunopathogenesis of RA.     

HLA class II transgenic mice as models of human diseases

Summary: Predisposition co develop Various autoimmune disorders has been associated with certain HLA class II molecules but there is a lack of information on che pathophysiological rule of HLA genes in conferring susceptibility Various experimental animal models of autoimmune disease have been studied to address the role of immune response genes. To study the interactions involved between class II molecules (DQ and DR) and define the immunologic mechanisms in various diseases, we generated HLA-DR and DQ transgenic mice that lacked endogenous class II molecules. The HLA molecules in these mice arc expressed on the cell surface and can positively select CD4+ T cells expressing Various Vβ T-cell receptors (TCR). A peripheral tolerance is maintained co transgenic HLA molecules thus indicating that these molecules act as self, Mouse co stimulatory and accessory molecules can interact with the HLA-peptide-TCR complex leading to efficient T-cell activation. In this review, we describe immunogenetic models for human diseases using these transgenic mice. Our studies show that HLA class II transgene-restricted T cells recognize the immunodominant antigens and peptide epitopes, similar to HLA class II-restricted human T cells. Thus these mice provide powerful tools to understand the role of HLA class II molecules in predisposition and onset of human diseases and to develop immunotherapy and vaccines.