Enhanced T-cell-activation due to combined stimulation by both endothelial cells and monocytes.

Mitogen-induced interleukin 2 (IL-2) secretion by T cells was greatly enhanced by the combined presence of endothelial cells (EC) and monocytes (AC). EC also altered the time course of IL-2 secretion by peripheral blood mononuclear cells (PBM) in response to mitogens. The response to EC did not require expression of HLA-DR antigen and occurred equally well in response to autologous EC. At least one live accessory cell was required to induce T cells to secrete IL-2. When added to T cells plus live AC, both fixed EC and EC supernatant partially reproduced the enhancing effect of EC. Surface membrane IL-1 was present on both live and fixed EC. However, active EC supernatant contained no detectable IL-1 activity. Anti-IL-1 abolished the enhancement of T-cell responses by fixed but not live EC.