CD38 EXPRESSION ON MOUSE T-CELLS - CD38 DEFINES FUNCTIONALLY DISTINCTSUBSETS OF ALPHA-BETA-TCR(-)CD8(-) THYMOCYTES()CD4()

We have examined CD38 expression on mouse lymphocytes using the rat mA b NIM-R5 and demonstrate that CD38 expression is restricted to similar to 8% of thymocytes. Although CD38 is absent from the majority of CD4 (+)CD8(-) and CD4(-)CD8(+) T cells, we detected a strong correlation b etween CD38 expression and alpha beta(+)CD4(-)CD8(-) T cells in the th ymus, with nearly 80% of alpha beta TCR(+)CD4(-)CD8(-)thymocytes being CD38(+). Using heat stable antigen (HSA) and CD38, we divided alpha b eta(+)CD4(-)CD8(-)thymocytes into four subsets: HSA(+)CD38(-), HSA(-)C D38(hi), HSA(-)CD38(low) and HSA(-)CD38(-). Two established characteri stics of ap TCR(+)CD4(-)CD8(-) cells, bias towards V(beta)8.2 TCR expr ession and high levels of IL-4 production, were used to establish a po ssible relationship between the above thymocyte subsets. Our present d ata show that the HSA(+)CD38(-) subset is not biased towards V(beta)8. 2 TCR expression whereas the HSA(-)CD38(-) subset does show this bias (similar to 47%). Neither of these subsets make IL-4 upon CD3 mediated stimulation. In contrast, the CD38(+) subsets are heavily biased towa rd V(beta)8.2 expression and produce large amounts of IL-4 upon stimul ation, particularly the CD38(low) cells. Taken together, these data su ggest that these four subsets represent various stages of a possible d ifferentiation pathway for alpha beta TCR(+)CD4(-)CD8(-) cells, with t he HSA(+)CD38(-) subset being the most immature while the HSA-CD38(low ) subset is the most functionally mature. These characteristics suppor t the view that alpha beta TCR(+)CD4(-)CD8(-) T cells represent an ind ependent lineage with a distinct, but as yet obscure, role in immunity .