C57BL/6 mice preferentially generate cytolytic T lymphocytes (CTL) to a limited number of immunodominant minor antigens and associated immunogenic peptides when primed with H2-matched Balb.B spleen cells despite multiple minor histocompatibility (H) antigen differences. We have examined the complexity of dominant H antigens recognized by these CTLs to estimate the number of peptides associated with single antigens. Peptides eluted from Kb molecules of lymphoblasts from Balb.B and CXB recombinant inbred (RI) strains were tested for sensitization of RMA-S cells for lysis by short-term C57BL/6 CTL lines specific for Balb.B and CXB strains. Anti-Balb.B CTLs recognized four Kb-bound peptides; subsets of these peptides were recognized by anti- CXB CTLs when tested with peptides from the respective CXB strains. Single peptides segregated independently among the CXB strains, confirming that single peptides were encoded by independently segregating alleles. These peptides were expressed in diverse inbred mouse strains and were recognized preferentially by C57BL/6 CTLs stimulated by different inbred mouse strains. This set of peptides was subclassified by their capacity to sensitize targets when presented in unfractionated mixtures of Kb-bound peptides. The peptide associated with the previously classified dominant CTT-2 antigen was the only peptide to strongly sensitize RMA-S cells for lysis under these conditions. These results suggest that dominant peptides have a wide strain distribution and may have a distinct advantage over dominated peptides in binding to class I molecules and/or in presentation to CTLs.
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