EFFECT OF STRONG AND WEAK HISTOCOMPATIBILITY ANTIGENS ON THE MIXED LYMPHOCYTE CULTURE REACTION IN RATS

Individual rats belonging to two different F2 crosses were serotyped for HI (AgB) determined antigens and tested in mixed lymphocyte culture (MLC) against parental strain rats. In agreement with the general contention that MLC reactivity is controlled solely by the major histocompatibility locus of the species, all HI different mixtures were found to stimulate, while HI identical mixtures failed to stimulate. The lack of MLC stimulation by minor loci antigens may be due to low frequency of antigen sensitive cells against these antigens. Immunization may be expected to increase their frequency and indeed in some combinations low but clear-cut stimulation was produced by non HI antigens after specific immunization. In the HI (different AS-AS2 combination an unexpected discrepancy was found between the relative antigenic strength as measured by MLC on one side and by the local graft-versus-host assay (12, 13) and by kidney graft survival on the other side. Possible reasons for this discrepancy are discussed.