An Lyt differentiated thymocyte subpopulation detected by flow microfluorometry

Abstract

DATA on the T-cell antigens, Lyt 1, 2, 3 (refs 1, 2), relating to functional T-cell subsets, suggest that some peripheral T cells express restricted Lyt phenotypes, that is, Lyt 1⁺23⁻ or Lyt 1⁻23⁺ (ref. 3). Evidence has been presented showing that two major subpopulations of lymphocytes, Lyt 1⁺ T cells and Lyt 23⁺ T cells, are committed to particular lines of functional differentiation in the immune response before encountering exogenous antigen in peripheral lymphoid tissue^4,5. It has been suggested that the two major subpopulations representing T-cell help (Lyt 1⁺) and T-cell cytotoxicity or suppression (Lyt 23⁺) arise in the periphery from peripheral Lyt 123⁺ cells⁶. Recent studies have concluded that as stem cells mature in the thymus, the thymic epithelium is important in determining which H–2 specificities the maturing T cells are able to recognise as self⁷. Previous cytotoxicity data have been interpreted as indicating that Lyt 1, 2, 3 antigens are expressed on each of most if not all, mouse thymocytes; that is, that most thymocytes are Lyt 123⁺ (refs 1–4, 8–10). However, the data presented here suggest that the commitment to differentiation of the Lyt 1⁺ or the Lyt 123⁺ phenotype, and thus presumably the relevant functional differentiation occurs before cell migration from the thymus. Using flow microfluorometry (FMF) and anti-Lyt antisera, we demonstrate a normal thymocyte subpopulation which is not expressing Lyt 2 or Lyt 3 antigens (Lyt 1⁺23⁻). This subpopulation represents a significant constant proportion (10%) of normal thymocytes which is markedly increased following in vivo cortisone treatment. The data also show that Lyt 1 expression, rather than being decreased on cortisone-resistant thymocytes (CRT), as would have been predicted from previous cytotoxicity data^2,8, is expressed in increased amounts on CRT.