defines functionally distinct subsets of ocp TCR+CD4"CD8 " thymocytes

We have examined CD38 expression on mouse lymphocytes using the rat mAb NIM-R5 and demonstrate that CD38 expression Is restricted to- 8 % of thymocytes. Although CD38 Is absent from the majority of CD4+CD8 " and CD4~CD8+ T cells, we detected a strong correlation between CD38 expression and af3+CD4"CD8- T cells in the thymus, with nearly 80 % of af3 TCR+CD4"CD8-thymocytes being CD38+. Using heat stable antigen (HSA) and CD38, we divided aP+CD4~CD8-thymocytes into four subsets: HSA+CD38", HSA-CD38hi, HSA-CD38|OW and HSA-CD38". Two established characteristics of a(3 TCR+CD4~CD8 ~ cells, bias towards Vp8.2 TCR expression and high levels of IL-4 production, were used to establish a possible relationship between the above thymocyte subsets. Our present data show that the HSA+CD38 ~ subset Is not biased towards Vp8.2 TCR expression whereas the HSA~CD38 ~ subset does show this bias (-47%). Neither of these subsets make IL-4 upon CD3 mediated stimulation. In contrast, the CD38+ subsets are heavily biased toward Vp8.2 expression and produce large amounts of IL-4 upon stimulation, particularly the CD3810 " cells. Taken together, these data suggest that these four subsets represent various stages of a possible differentiation pathway for o0 TCR+CD4"CD8- cells, with the HSA+CD38" subset being the most immature while the HSA~CD38|OW subset is the most functionally mature. These characteristics support the view that af3 TCR+CD4~CD8 ~ T cells represent an independent lineage with a distinct, but as yet obscure, role in Immunity