Analysis of class I MHC antigens in the rat by monoclonal antibodies.

Monoclonal antibodies (mAb) were made against class I MHC antigens of the i (mAb 42,70,39) and u (mAb 68-D) haplotypes in the rat by using specific strain combinations in order to obtain reagents for identifying the products of the RT1.An, RT1.Au, and RT1.Eu loci. These antibodies were hemagglutinating only; were IgG except for mAb 68-D3, which had a defective heavy chain; reacted identically with MHC-congenic strains and with their inbred donor strains; and precipitated class I MHC antigens. Strain distribution, sequential immunoprecipitation, and peptide mapping studies were used to define the specificities of the mAb, and the assignments were checked by comparing the specificities of the mAb with those of haplotype-specific alloantisera. The specificities were the following: mAb 42, An; mAb 68-D, Au; mAb 70, Eu; and mAb 39, an antigen encoded by a locus different from A and E. This new locus was designated RT1.F, and the allele detected by mAb 39, as Fa. The serologic data place RT1.F between RT1.A and RT1.D. The plasma membranes of DA.1I(BI) lymphocytes contain comparable amounts of An, Eu, and Fa antigens but express them on the cell surface in the order An much greater than Eu greater than Fa.