Based on the susceptibility of DR1 Tg mice to CIA and their T cell proliferative response to hCII, we proceeded to identify the hCII antigenic determinants bound and presented to T cells by the DR1 molecule. of DR1-specific therapies for RA. It is well established that strong correlations exist between the expression of specific MHC alleles and increased susceptibility to certain immune-mediated diseases. Some of these diseases, such as ankylosing spondylitis, have been shown to be associated with the expression of a specific class I allele (HLA-B27), whereas many other diseases are strongly linked with the expression of certain class II alleles. One autoimmune disease that has been studied extensively for its association with class II alleles is usually rheumatoid arthritis (RA)1. Many years ago it was noted that a strong correlation existed between the expression of HLA-DR1 or DR4 and an increased risk of developing RA (1C3). We now know that in most cases, this increased susceptibility is usually associated with the DRB1 locus, and more specifically with the presence of the DRB1*0101, DRB1*0401, DRB1*0404, or DRB1*0405 genetic allotypes (4). Sequence analysis of these alleles revealed that each encodes a similar amino acid sequence within residues 67C74, termed the shared epitope (5, 6). The role of this shared epitope has been the focus of several hypotheses (5C8); however, little is known about how it affects the function of the DR molecules and confers susceptibility to RA. Although the etiology of RA remains unsolved, several antigens have been proposed to be involved in the stimulation of pathogenic T cells in RA. Viral proteins such as CMV and EBV have been implicated (9, 10), as well as autologous proteins normally expressed in diarthroidial joints. One autologous protein, type II collagen (CII), has received considerable attention as a potential antigen in RA because of both its ability to induce experimental autoimmune arthritis in MRS1186 several animal models (11C13), and the demonstration of CII-specific immunity in the diseased synovium and cartilage of RA patients (14C17). Although it MRS1186 has not been confirmed that autoimmunity to CII initiates RA, it seems clear that at least some of the autoimmunity in RA is usually directed towards CII. The difficulty, however, has been in determining the relationship between immunity to CII and the role of the class II alleles that confer susceptibility to RA. One approach to analyzing the role of the HLA-DR molecules in RA is usually to establish them as transgenes in animals. Using transgene models, antigens proposed to be recognized by DR-restricted T cells can be tested for their ability to induce an immune response as well as elicit an experimental autoimmune disease. In addition, HLA transgenic (Tg) mice facilitate the identification of peptides presented by DR molecules from an antigen in question, especially from human proteins. Toward these aims, we have established transgene expression of a chimeric (human/ mouse) HLA-DR1 molecule (DRB1*0101, DRA1*0101) in the arthritis-resistant B10.M (H-2f) mouse in an attempt to determine if the DR1 molecule is usually capable of presenting peptides derived from human CII (hCII), and if this presentation would lead to the development of an experimental autoimmune arthritis. Here we report that this chimeric DR1 transgene is usually fully functional as a class LAMC2 II restriction element in the mouse and strongly confers susceptibility to an autoimmune, collagen-induced arthritis (CIA) after immunization with hCII. In contrast, non-Tg control mice were totally resistant MRS1186 to arthritis induction and mounted only a negligible immune response to hCII. The autoimmune arthritis that develops MRS1186 in the DR1 Tg mice is usually accompanied by strong T and B cell responses to hCII. Virtually all of the DR1-restricted T cell responses to hCII are directed to two antigenic determinants, with the core of the dominant determinant located within CII(263C270). Antibodies produced by DR1 Tg mice after hCII immunization bound strongly to both the immunogen, hCII, and the autoantigen murine CII (mCII). These data indicate that this DR1 molecule is usually capable of binding and presenting peptides derived from hCII, supporting the hypothesis that autoimmunity to CII plays a role in the pathogenesis of RA. Materials and Methods Animals. (C57BL/6 SJL/J)F2 and B10.M/Sn (H-2f?) mice were obtained from (Bar Harbor, ME). Generation of Tg Mice Expressing DR1. Chimeric (human/mouse) DRB1*0101 constructs were made using the chimeric DRB1*0401 chain gene construct that has been previously described (18). To generate the chimeric DRB1*0101 gene construct, the plasmid made up of the chimeric.