A structural somatic variant of the Kk antigen is generated by point mutation

We have previously selected structural variants of the K^k antigen from a (C3 × D2)F₁ T-cell lymphoma. Those mutants were identified by the loss of certain epitopes defined by monoclonal antibodies. The variant K^k molecule from HK13.S3 cells is no longer recognized by 40% of the trinitrophenyl-specific, K^k-restricted cytotoxic T lymphocytes. Here we report on the primary structure of the altered K^k molecules from the cell line HK13.S3. Comparison with the parental K^k reveals a single base pair exchange, GCG to GTG, that results in an alanine to valine exchange in position 40 of the protein. This observation emphasizes that minor structural alterations in class I molecules may have a strong effect on the H-2-restricted T-cell response.