Induction of proliferation of human T cells and T-cell blasts by monocyte-derived factors and lectin

Highly purified populations of human T cells and of human monocytes were obtained using a combination of physical separation procedures-plastic adherence, nylon wool fractionation, and fractionation over Percoll density gradients-and of complement-dependent lysis with mouse monoclonal antibody to human T cells (anti-T3) and with rabbit antihuman monocyte and rabbit antihuman p 29, 34 antisera. The proliferative response of purified human T cells to concanavalin A (Con A) was absolutely dependent on the presence of a radio-resistant DR-bearing monocyte. Following stimulation with Con A a DR-bearing monocyte secreted a growth factor which in the presence of lectin induced proliferation in T cells and in T cell growth factor (TCGF)-dependent T-cell blasts. The monocyte-derived growth factor differed from TCGF but in the presence of lectin induced TCGF secretion by T cells. It exhibited properties very similar to those of interleukin-1.