Molecular characterization of T-cell antigen receptor expression by subsets of CD4- CD8- murine thymocytes

Abstract

Precursors of all T-lineage cells are found in a population of thymocytes that lack the CD4 and CD8 surface glycoproteins. These 'double-negative' thymocytes are markedly heterogeneous in their expression of other surface markers and include cells at various stages of development. In this study, CD4- CD8- adult murine thymocytes were separated into subsets based on the expression of the 'heat stable antigen' (HSA) and of Ly 1 (CD5). The sorted subsets were analyzed directly (without prior expansion in culture) for T-cell antigen receptor (TcR) gene rearrangement and mRNA expression and for TcR and CD3 cell-surface protein expression. Very little surface CD3 or TcR expression was detected on the major HSA+ Ly 1(low) subset. However, the HSA+ Ly 1(high), HSA- Ly 1(high), and HSA- Ly 1(low) subsets all contained cells with surface expression of CD3 and TcR. In contrast to previous studies, we found no subset that exclusively expressed either the αβ or γδ heterodimer, although the ratio of αβ+ to γδ+ varied widely. Two of these three subsets (HSA- Ly 1(low) and HSA- Ly 1(high)) showed very high usage of Vβ8 gene products in the αβ heterodimer, but nevertheless included ~15% non-Vβ8 αβ forms. All CD4- CD8- subsets were found to have extensively rearranged their TcRγ genes and to express γ mRNA. Expression of a high ratio of mature [1.3 kilobases (kb)] to truncated (1.0 kb) β message and presence of α message was largely restricted to subsets with TcR αβ surface expression.