Interleukin-4 mediates CD8 induction on human CD4+ T-cell clones

CD4 and CD8 antigens are simultaneously expressed on most of the cortical thymocytes, that weakly express the T-cell antigen receptor(TCR)/CD3 complex1,2. Mature peripheral T cells, however, strongly express the TCR complex and are positive for either CD4 or CD8. Nevertheless, a small percentage of peripheral CD3+ T cells express CD4 and CD8 simultaneously3. These mature, double positive cells could be intermediates between CD4+CD8+ thymocytes and mature, single positive T cells, or they may originate from single positive T cells that acquire either CD4 or CD8. Here we report that activation and culturing of cloned CD4+ T cells in interleukin-4 (IL-4), results in the acquisition of CD8 due to its de novo synthesis. The IL-4-induced co-expression of CD8 on CD4+ T cells is reversible, in that CD8 disappeared from double positive T-cell clones isolated in IL-4, when they were cultured in IL-2. CD8 induced by IL-4 can be functional as a monoclonal antibody to CD8 inhibited anti-CD3-mediated cytotoxicity by a double positive T-cell clone.