Estimates of the precursor frequency of cytotoxic T lymhocytes against antigens controlled by defined regions of the H-2 gene complex: comparison of the effect of H-2 differences due to intra-H-2 recombination vs mutation.

Lymph node cells were sensitized in a limiting dilution assay against B10.D2 (H-2d) and the frequency of cytotoxic T lymphocyte (CTL.P) precursors was determined. A mean CTL.P frequency of 0.047% was observed when responding strains differed from the stimulators at the entire H-2 gene complex. When intra-H-2 recombinant strains were sensitized against B10.D2, lower frequencies of CTL.P were observed. Responding strains that differed from the stimulators at the H-2K-end only had 2- to 6-fold more CTL.P compared to strains sensitized against the D-end only. In order to study the CTL.P frequency against minor antigenic differences, the B10.D2 (M504-H-2da) mutant strain, which carries a mutation with an antigenic gain-loss in the D-region of H-2d, was examined. This mutant showed an identical CTL.P frequency against H-2d as H-2D-end recombinant strains. Therefore, this H-2 mutant (M504) has either undergone extensive mutation or the qualitative nature of the antigenic loss in this strain results in a high CTL.P frequency against the strain of origin.