An epitope on class II antigens that is maintained across species barriers and important in immunologic functions.

Serological, functional, and chemical analyses of murine class II antigens were performed using a unique monoclonal antibody, 1E4, which was obtained from a rat-mouse hybridoma. 1E4, which is specific for a monomorphic determinant on HLA-DR antigens in humans and a polymorphic determinant on RT1-Da antigens in rats, detected class II antigens on the cells from mice carrying H-2 haplotypes of b, d, p, q, u, v, k, j, r, but not those with f or s haplotypes. Analysis of two-dimensional gel electrophoresis revealed that 1E4 monoclonal antibody recognized at least Ek/b, d, k and Ab, d molecules. 1E4 blocked the T cell proliferative responses to beef insulin and TGAL in B10 and BALB/c mice, as well as proliferative responses to GLT in BALB/c mice and to PPD in C3H/He mice, as had been demonstrated in other species. Furthermore 1E4 inhibited MLR to stimulator cells that expressed Ab, d or Ek/b, k, d molecules. Taken together, these findings indicate that an epitope detected by 1E4 on class II antigens has been well preserved across species barriers. This epitope may play a major role or be closely related to the functional site that is involved in recognition of nominal antigens by T cells.