Studies of the MHC-linked "CT" alloantigenic system in rats. II. Evidence for more than one locus and several different determinants.

Previous studies have defined a novel, MHC-linked alloantigenic system in the rat (CT) detectable with cytotoxic T cells (CTL) generated by alloimmunization and restimulation using strain combinations thought to be RT1-compatible, for instance, Lewis and Fischer 344. CTLs generated in this way are able to lyse targets from a variety of different strains without any evidence of MHC-restricted interactions, and yet these CT determinants possess properties unlike conventional class I and class II MHC gene products. The present studies employ cold target competition assays to derive a minimal estimate of the number of different CT determinants detected with Lewis anti-Fischer 344 CTLs, the number of loci involved in their expression, and their strain distribution. The results indicate that Lewis anti-Fischer CTLs define at least four different determinants encoded by at least two different loci.