Somatic cell variants of H-2Kb: a point mutation in the first extracellular domain results in altered immune recognition.

A cell-surface-associated variant H-2K product was expressed by an Abelson virus-induced pre-B-cell line after chemical mutagenesis with ethyl methane sulfonate. The variant cell line (R8.313) was previously demonstrated to have altered allodeterminants in Kb as demonstrated by both Kb-specific monoclonal antibody binding and alloreactive cytotoxic T lymphocyte (CTL) cytolysis. The mutant H-2Kb gene from R8.313 was cloned and characterized in detail. DNA sequence analysis of the region of the gene corresponding to the three extracellular domains identified a single point mutation resulting in a leucine-to-phenylalanine substitution at amino acid residue 82. The site of mutation within the alpha 1 domain was confirmed by oligonucleotide hybridization analysis. Mouse L-cell fibroblasts transfected with the mutant gene were recognized with the same monoclonal antibody binding and CTL lytic pattern as the R8.313 cell line, confirming that the altered phenotype of the mutant cell line was due to a point mutation in the H-2Kb gene. These data further extend the hypothesis that the region of amino acid residues 70-90 in the alpha 1 domain is important in the formation of both antibody and CTL-defined recognition structures on major histocompatibility complex class I molecules.