CD4⁺ murine T cells develop from CD8⁺ precursors in vivo

Abstract

The adult murine thymus contains four subpopulations of thymocytes defined by the T-cell surface antigens CD4 (L3T4) (a marker of helper T cells) and CDS (Lyt2) (a marker of cytotoxic/suppressor T cells): CD4⁺8⁻ and CD4^–8⁺ (single positives), CD4⁺8⁺ (double positives) and CD4⁻8⁻ (double negatives). To understand how T cells develop in the thymus, it is important to determine the lineage relationships among these subpopulations. In particular, the status of double positives, which make up ∼80% of the total thymocyte population¹, has long been controversial. Some propose that double positives are 'dead-end cells' that all die in the thymus, perhaps because they have been rejected by some selection process. Others suggest that, although most double positives die in the thymus, some develop into the more mature single positives that leave the thymus^1–5. The experiments presented here show that repeated injections of anti-CD8 monoclonal antibodies block the development of CD4⁺ cells, demonstrating that these cells develop from CD8⁺ precursors, probably double positive thymocytes, in vivo.