Cytolytic T lymphocyte precursors reactive against mutant Kb alloantigens are as frequent as those reactive against a whole foreign haplotype.

Minimal frequencies of CTL-P in C57BL/6 spleen responding to H-2 mutational or whole haplotype differences were estimated by using a limiting dilution MLC technique. The frequency of CTL-P reacting against cells from each of three different H-2Kb mutant strains, carrying H-2 haplotypes ba, bg2, or bh, was determined to be within the range of frequencies of CTL-P directed against cells from strains carrying the independently derived H-2d and H-2k haplotypes.