Prothymosin alpha 1 effects on IL-2-induced expression of LFA-1 on lymphocytes and their adhesion to human umbilical vein endothelial cells

Prothymosin alpha 1 (Pro alpha 1) is known to stimulate in vitro and in vivo natural killer (NK) and lymphokine (IL-2)-activated killer (LAK) cells against tumor cells. in this process, LAK cells first adhere to endothelial cells in vivo, raising the question whether Pro alpha 1 affects this interaction as well. The binding ability of peripheral blood lymphocytes (PBL) to human umbilical vein endothelial cells (HUVEC) was increased by incubation with IL-2 in a concentration-dependent manner, reaching a maximal value at 20U/ml IL-2. Although Pro alpha 1 alone was without any stimulating effect, it significantly increased PBL binding to unstimulated HUVECs in combination with suboptimal IL-2 (5 and 10 U/ml). The combination of Pro alpha 1 (1 mu g/ml) and 5 U/ml or 10 U/ml IL-2 is as effective as 10 U/ml or 20 U/ml IL-2 alone. This Pro alpha 1 effect on IL-2-activated lymphocytes was found to be augmented on IL-1 or tumor necrosis factor (TNF)-alpha-activated endothelial cells. Analyzing the effect of Pro alpha 1 on IL-2-activated lymphocytes by flow cytometry revealed an increase of CD16, CD56, and CD18 surface marker expression, whereas CD3, CD11a/b, CD49d, and CD54 were not affected. In conclusion,Pro alpha 1 functions as a mediator of the adhesion of IL-2-activated lymphocytes to HUVECs.