HLA-DR4 (DRB1-ASTERISK-0401) TRANSGENIC MICE EXPRESSING AN ALTERED CD4-BINDING SITE - SPECIFICITY AND MAGNITUDE OF DR4-RESTRICTED T-CELL RESPONSE

Optimum function of HLA-DR molecules in transgenic mice requires effic ient interaction between the class II molecules on APCs and CD4 on T c ells. Residues 110 and 139 of the second domain of class LT molecules are considered to be critical for recognition of CD4, We generated an HLA-DR4 beta(NT) transgene construct in which positions 110 and 139 we re altered to resemble endogenous mouse H2 A beta molecules. This cons truct was introduced into (B10 x SWR) embryos, and DR4 beta(NT) transg enic mice were produced. The transgene was transferred into B10.RFB3 ( E beta(0) E alpha(p)) mice. The transgene-encoded DR4 beta molecules p aired with endogenous E alpha chains to form stable DR4 beta/E alpha d imers expressed on the cell surface, The hybrid dimers showed similar Ag-binding specificity to MLA-DR4 molecules and positively selected CD 4(+) T cells in vivo. Immunization of HLA-DR4 beta(NT) transgenic mice with DR4-restricted peptides induced T cell proliferation in vitro. W hile the purified T cells from DR4 beta(NT) transgenic mice responded strongly to the HA(307-319) presented by M12C3 transfectants expressin g altered DR4 beta/E alpha heterodimers, the response to the same pept ides presented by transfectants expressing wild-type DR4 beta/E alpha molecules was substantially reduced. Taken together, these data confir med in vitro studies on the importance of these residues in CD4-MHC cl ass II interaction. The altered HLA-DR4 beta transgenic mice were able to overcome the species barrier and generate efficient HLA-DR4-restri cted CD4-specific immune responses. Thus, residues 110 and 139 were cr itical for the interaction of class II with CD4 T cells during thymic selection as well as peripheral immune responses.