DISTRIBUTION OF LY-6C ON LYMPHOCYTE SUBSETS .1. INFLUENCE OF ALLOTYPEON T-LYMPHOCYTE EXPRESSION

The expression patterns of the Ly-6C Ag were examined on splenic and t hymic lymphocyte subsets of Ly-6.1 and Ly-6.2 strains of mice using th e rat mAb 15.1. Ly-6C is expressed on subsets of CD4(+) and CD8(+) spl enocytes, and a portion of NK cells. Within the splenic and lymph node CD4(+) T cell compartment, Ly-6C expression is restricted to Ly-6.2 s trains of mice, and is present on a subset of naive cells, Ly-6C is ex pressed on the majority of peripheral CD8(+) T cells in both Ly-6.1 an d Ly-6.2 strains, and is found primarily on the Ag-experienced subset. In the thymus, Ly-6C is present on subpopulations of CD4(-)CD8(+), CD 4(-)CD8(-), and CD4(+)CD8(-) cells. Ly-6C(+)CD4(-)CD8(+) thymocytes sh ow a mature phenotype, while Ly(-)6C(+)CD4(-)CD8(-) and Ly6C(+)CD4(+)C D8(-) thymocytes appear to be part of the recently described NK1.1(+) alpha beta TCR+ population. On account of the marked differences in Ly -6C expression on peripheral CD4(+) T cells from Ly-6.1 and Ly-6.2 str ains of mice, additional experiments were undertaken to assess Ly-6C e xpression in parental and Ly-6.1 x Ly-6.2 F-1 mice. Neither phenotype dominated in the F-1 offspring, with frequencies of Ly-6C(+)CD4(+). sp lenocytes falling in the intermediate range. Further experiments compa red the staining patterns of the rat anti-pan Ly-6C (Ly-6.1 and Ly-6.2 ) Ab with a mouse anti-Ly-6.2 allotype specific Ab, with emphasis on b oth Ly-6.2 and Ly-6.1 x Ly-6.2 F-1 mice. The results demonstrate the p resence of lymphocytes that express the pan form of Ly-6C but not the form recognized by the alloantibody. This latter finding suggests the presence of more than one form of the Ly-6C Ag.