The Localized Primary Cytotoxic T‐cell Response to Cells Expressing Minor Histocompatibility Differences

Cytotoxic T lymphocytes (CTL) are able to eliminate P815 (DBA/2) mastocytoma cells growing in cerebrospinal fluid of BALB/c H-2-compatible but minor histocompatibility (H) antigen-different mice and in H-2-incompatible C3H/He mice. We examined the magnitude of the primary CTL response to multiple, minor H antigens and to determinants of the major histocompatibility complex (MHC) by using a direct cytolytic assay and limiting-dilution analysis to estimate CTL frequency. By these criteria, no obvious differences emerged, and the responses appeared comparable at the site of inflammatory process, despite differences in the number of clonal progenitors. Experiments with radiation chimeras showed evidence of a strong cytotoxic T-cell response against P815 cells in [(ddd X bbb)F1----ddd] and (F1----bbd), but not in (F1----bbb) radiation chimeras. Therefore, this cytotoxic T-cell response against minor H antigens obeys the postulated rules for thymic restriction of precursors. Compatibility at the H-2 D-end of the MHC is apparently sufficient to ensure a strong response.