Close association between particular I region-determined cell surface antigens and Ir gene-controlled immune responsiveness to synthetic polypeptides in wild rats.

The relationship between major histocompatibility complex (MHC) and genetic control of immune responsiveness to the synthetic polypeptides (T,G)-A--L [poly-(LTyr,LGlu)-poly(DLAla)--poly(LLys)] and (H,G)-A--L [poly(LHis,L-Glu)-poly-(DLAla)--poly(LLys)] has been studied in 26 wild rats. The major histocompatibility complex (MHC) genotype frequencies observed were not different from those expected according to the Hardy-Weinberg formula. More than half of the wild rats carried MHC-linked responder Ir-TGAL and Ir-HGAL genes. High or intermediate responsiveness to (T,G)-A--L and high responsiveness to (H,G)-A--L were always found to be associated with particular I region-determined cell surface antigens. These antigens could be identified serologically and by primary and secondary mixed lymphocyte reactions, and were similar or identical to I region products of (T,G)-A--L high responder or (H,G)-A--L intermediate responder inbred rat strains. The strong association between cell surface antigens and immune responsiveness could be due to linkage disequilibrium or to pleiotropy. Since the same I region-determined cell surface structure could be associated either with high or intermediate anti-(T,G)-A--L antibody titers, the presence of the Ia antigen(s) identified did not seem to guarantee high antibody responsiveness to the test antigen.