Epitopes on H-2Dd somatic cell mutants recognized by cytotoxic T cells.

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Abstract
Several cell lines that express an altered H-2Dd molecule were generalized. These cell lines, which were selected by the failure to express the serological specificity reacting with the monoclonal antibody 34-2-12, have also undergone alterations in epitopes recognized by CTL [cytotoxic T-lymphocytes]. One of the mutants, 2.12-4 was not killed by an allogeneic anti-Dd CTL line, CTLL-A2, even though this line was cytotoxic for the parental cell line and 2 other 34-2-12- mutant lines. Two of the 34-2-12- mutant lines had an identical serological profile using other monoclonal Dd antibodies, these 2 mutants differed markedly in their susceptibility to cytotoxicity by CTLL-A2. In addition to the determinants recognized by allogeneic CTL the effect of the mutation on the determinants involved in restricting the anti-FITC [fluorescein isothiocyanate] modified-self-cytotoxic response was examined. An anti-FITC-Dd CTL line did not react with 2 of the mutants and reacted only weakly with the other mutant, demonstrating not only that the Dd epitopes recognized by this cell line and the allogeneic CTL were different, but also that it is possible for a H-2 class I molecule to express epitopes recognized by allogeneic CTL but not epitopes that function as restricting elements to certain antigens. The observation that both T cell- and B cell-defined determinants were altered in these mutant cell lines is in contrast to the findings, with the mutant mouse strains which were selected for by changes in T cell-defined determinants, which show few, if any, alterations to serological specificities. Characterization of T cell-recognized epitopes expressed on serologically selected somatic cell variants may prove to be most useful for the study of structure-function relationships of H-2 class I molecules.