Cim: an MHC class II-linked allelism affecting the antigenicity of a classical class I molecule for T lymphocytes

Two alleles at the major histocompatibility complex (MHC)-linked locus cim determine gain and loss changes in the rat RT1.A^a class I molecule which affect its structure both as an alloantigen and as a restriction element. Alleles at the cim locus also influence the post-translational modification of RT1.A^a. These effects may reflect the participation of the cim gene product in the processes of peptide loading or assembly of RT1.A^a. In this study we have used the discriminating RT1.A^a-specific monoclonal antibody JY3/84, as well as cytotoxic T cells raised in appropriate combinations, to determine the cim alleles of eight haplotypes in 15 independent inbred strains of rat. We have also employed the same techniques to analyse a panel of F1 hybrid animals derived from various MHC recombinant strains. These experiments map the cim locus to the class II region of RT1, probably between the DP-related genes (RT1.H) and the DQ-related RT1.B. Address correspondence and offprint requests to: G. W. Butcher.