IL-10 and IL-3 synergize to cause proliferation of human T cells.

Interleukin-3 (IL-3) is a well-documented haemopoietic growth factor, but its effects on T-cell function are less clear. Although this cytokine is a potent growth factor for CD4- CD8- alpha beta T-cell receptor-expressing cells, it has few known effects on single-positive T cells. In this report it is shown that IL-3 synergizes with IL-10 to induced proliferation of T-cell lines and single-positive clones. Specificity was verified using blocking anti-IL-10 and anti-IL-3 neutralizing antibodies. This induction of proliferation was dose dependent. Taken together the results imply that IL-3 can act as a growth factor for T-cell lines and single-positive T-helper type-1 (Th1) CD4+ clones in the presence of a cofactor, IL-10, a cytokine that has been documented as being predominantly a T-cell inhibitory, and not proinflammatory, cytokine.