CLASS-I DEPENDENCE OF THE DEVELOPMENT OF CD4+CD8-NK1.1+ THYMOCYTES

A small subset of functionally active CD4(+)CD8(-) thymocytes express the NK1.1 marker, as do most CD4(-)CD8(-)NK1.1(+) thymocytes. Previous studies have failed to implicate a role for major histocompatibility complex (MHC) or related molecules in the selection of the CD4(+)CD8(-)K1.1(+) subset. We report here that the development of most of these cells is sharply reduced in class I-deficient mice, but not in class II-deficient mice. Hence, some CD4(+) T cells are class I dependent and not class II dependent. Unlike conventional T cells, however, the development of NK1.1(+) thymocytes in both the CD4(+)CD8(-) and CD4(-)CD8(-) subsets is dependent on class I MHC expression by hematopoietic cells and not thymic epithelial cells. We propose that these populations are selected by nonpolymorphic class Ib or CD1 molecules.