Zanelli, Eric

Abstract Recently, we have proposed that the combination of HLA-DQ and -DR alleles is responsible for the association of the HLA class II region with rheumatoid arthritis (RA). According to this model, some HLA-DQ alleles, namely DQ4, DQ7, DQ8, and DQ9, predispose carriers to severe RA, but a self peptide of sequence KDILEDERAAVDTYC from the third hypervariable (HV3) region of some DRB1 alleles, including DRB1*0402, can protect from the disease if presented by DQ molecules. This model implies that DQ4, DQ7, DQ8, and DQ9 should be able to present a set of common peptides, despite polymorphisms in their Ag binding groove. In the present study, we have further analyzed the immunogenicity of the DRB1*0402 HV3 peptide in DQ8-transgenic mice. We found that the motif DERAA guarantees DQ8-restricted immunogenicity, and that R is the main anchor residue for binding of the DRB1*0402 peptide to DQ. Interestingly, the p1 pocket that probably controls binding of the R residue is identical in all four RA-associated DQ molecules. Our results imply that the association of RA with some DR subtypes can be explained by their linkage with DQ alleles displaying a binding site for similar “arthritogenic” peptides.

Collagen-induced arthritis (CIA) is an animal model of autoimmune inflammatory polyarthritis that has features similar to rheumatoid arthritis (RA). Much like RA, susceptibility to mouse CIA is influenced by the major histocompatibility complex (MHC), H-2, and restricted to the H-2q and H-2r haplotypes. Whereas the role of the H-2A molecule in susceptibility to CIA is well established, little is known about the role of H-2E molecule in the disease. In this study, we analyzed the effect of a transgenic E beta d molecule on CIA susceptibility in a recombinant mouse B10.RQB3, which expresses the CIA susceptible Aq genes and an Eak gene, but does not produce an E molecule since Ebq is nonfunctional. In the presence of an Ebd transgene, a viable E molecule is generated. Whereas B10.RQB3 were susceptible to CIA, B10.RQB3-E beta d+ showed a dramatic reduction in the incidence of arthritis as well as a decrease in the level of anti-mouse and anti-bovine CII antibodies in their serum. No clear cut differences in the expression of T cell receptor (TCR) V beta was observed between E beta d+ and E beta d- transgenic mice. Mechanisms underlying the protective effect of E beta d transgenic molecule on CIA may shed light on how HLA-DR molecules influence human RA.

The major histocompatibility complex class II genes play an important role in the genetic predisposition to many autoimmune diseases. In the case of rheumatoid arthritis (RA), the human leukocyte antigen (HLA)-DRB1 locus has been implicated in the disease predisposition. The "shared epitope" hypothesis predicts that similar motifs within the third hypervariable (HV3) regions of some HLA-DRB1 alleles are responsible for the class II-associated predisposition to RA. Using a line of transgenic mice expressing the DQB1*0302/DQA1*0301 (DQ8) genes in the absence of endogenous mouse class II molecules, we have analyzed the antigenicity of peptides covering the HV3 regions of RA-associated and nonassociated DRB1 molecules. Our results show that a correlation exists between proliferative response to peptides derived from the HV3 regions of DRB1 chains and nonassociation of the corresponding alleles with RA predisposition. While HV3 peptides derived from nonassociated DRB1 molecules are highly immunogenic in DQ8 transgenic mice, all the HV3 peptides derived from RA-associated DRB1 alleles fail to induce a DQ8-restricted T-cell response. These data suggest that the role of the "shared epitope" in RA predisposition may be through the shaping of the T-cell repertoire.

T helper 1 cells play a major role in protective immunity against mycobacterial pathogens. Since the antigen (Ag) specificity of CD4 + human T cells is strongly controlled by HLA class II polymorphism, the immunogenic potential of candidate Ags needs to be defined in the context of HLA polymorphism. We have taken advantage of class II-deficient (Ab 0 ) mice, transgenic for either HLA-DRA/B1*0301 (DR3) or HLA-DQB1*0302/DQA*0301 (DQ8) alleles. In these animals, all CD4 + T cells are restricted by the HLA molecule. We reported previously that human DR3-restricted T cells frequently recognize heat shock protein (hsp)65 of Mycobacterium tuberculosis , and only a single hsp65 epitope, p1–20. DR3.Ab 0 mice, immunized with bacillus Calmette–Guérin or hsp65, developed T cell responses to M. tuberculosis , and recognized the same hsp65 epitope, p1–20. Hsp65-immunized DQ8.Ab 0 mice mounted a strong response to bacillus Calmette–Guérin but not to p1–20. Instead, we identified three new DQ8-restricted T cell epitopes in the regions 171–200, 311–340, and 411–440. DR3.Ab 0 mice immunized with a second major M. tuberculosis protein, Ag85 (composed of 85A, 85B, and 85C), also developed T cell responses against only one determinant, 85B p51–70, that was identified in this study. Importantly, subsequent analysis of human T cell responses revealed that HLA-DR3+, Ag85-reactive individuals recognize exactly the same peptide epitope as DR3.Ab 0 mice. Strikingly, both DR3-restricted T cell epitopes represent the best DR3-binding sequences in hsp65 and 85B, revealing a strong association between peptide-immunodominance and HLA binding affinity. Immunization of DR3.Ab 0 with the immunodominant peptides p1–20 and p51–70 induced T cell reactivity to M. tuberculosis . Thus, for two different Ags, T cells from DR3.Ab 0 mice and HLA-DR3+ humans recognize the same immunodominant determinants. Our data support the use of HLA-transgenic mice in identifying human T cell determinants for the design of new vaccines.