Brief Definitive Report Human Cd3 + T Lymphocytes That Express Neither Cd4 nor Cd8 Antigens

Differential expression o f the CD4 and CD8 antigens on T lymphocytes has been used as a basis to construct models of thymic differentiat ion, and to identify functionally distinct subsets o f T cells (1, 2). In the thymus, most cells coexpress both CD4 and CD8, while minor subpopulations express the phenotypes CD4,8; CD4+,8-; and CD4,8 + (1, 2). It has been proposed that dur ing thymic on togeny CD4,8 precursor cells different iate into CD4÷,8 + thymocytes. Upon maturat ion, CD4+,8 + thymocytes acquire the C D 3 / T i complex and presumably lose ei ther CD4 or CD8, then CD3÷,4+,8 and CD3+,4-,8 + T lymphocytes migrate into per ipheral tissues (1, 2). Mature CD3+,4+,8 T cells augment Ig secretion by B lymphocytes and facilitate the generat ion of cytotoxic T cells, whereas CD3+,4-,8 + T cells predominate ly mediate cytotoxicity and immune suppression (3, 4). In general, antigenic recognit ion by CD4 + T cells is restricted by class II MHC gene products , whereas antigenic recognit ion by CD8 ÷ cells is restricted by class I MHC antigens (5, 6). It has been generally accepted that all per ipheral T cells express e i ther CD4 or CD8, with a minor population expressing both antigens. However , we have recently observed that a small subset o f human peripheral blood CD3 + T lymphocytes express nei ther CD4 nor CD8. Herein , we describe the characteristics o f this unique subset of T cells.