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

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Abstract
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,LGlu)‐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 associations 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.