Cytotoxic T lymphocytes of the rat are predominantly restricted by RT1.A and not RT1.C-determined major histocompatibility class I antigens.

Two types of biochemically defined class I major histocompatibility complex (MHC) antigens are found in the rat, RT1.A antigens that are ubiquitously expressed and RT1.C antigens which so far are detectable only on certain cell types, notably B and T lymphocytes. It is shown that the cytotoxic T lymphocyte response to minor H antigens of the LEW strain, including the H-Y antigen, and to TNP-modified syngeneic lymphoid cells is restricted by RT1.A but not RT1.C gene products. This conclusion is based on bulk culture assays including cold target inhibition tests and limiting dilution experiments using recombinants between the RT1a and RT1u haplotypes. The possibility that class I MHC antigens exist which have no major restriction function is discussed.