Co-expression of the CD8 receptor in a human CD4+ T-cell clone influences proliferation, cytosolic Ca2+ release and cytokine production

In normal human subjects a small proportion of peripheral blood T-cells simultaneously express both CD4 and CD8 differentiation antigens. In this study we characterized a subset of CD4+ clones, from a healthy donor, that is specific for the thyrotropin receptor (TSHR) and that showed cells co-expressing the CD8 receptor. To address whether the expression of the CD8 receptor on the cell membrane was associated to differences in the physiology of the T-cells, we isolated, from the same clone, CD4 single positive (SP) cells from those co-expressing CD4/CD8 receptors (DP cells) and stimulated them in vitro with antigen presenting cells (APC) carrying TSHR. The results demonstrated that CD8 co-expression has a profound effect on the physiology of T helper (Th) cells. In comparison to cells expressing the CD4 receptor alone, DP T-cells showed: (1) increased proliferation; (2) higher and more sustained release of free Ca2+ in the cytosol, under stimulus; (3) lower levels of IL-2 and IL-4 released in the supernatants; (4) increased amounts of IFN-gamma released.