Phorbol ester-stimulated T lymphocytes show enhanced adhesion to human endothelial cell monolayers

Phorbol esters have been used to study changes in the adhesiveness of T cells to endothelial cells (EC) after activation. The phorbol esters 12-O-tetra-decanoylphorbol-13-acetate (TPA) and 4-beta-phorbol-12,13-dibutyrate (P(Bu)2), but not the biologically inert 4-alpha-phorbol-12,13-didecanoate, strongly increased the binding of 51Cr-labeled T cells to human umbilical vein EC monolayers in microtiter wells. Binding to fibroblasts and gelatin-coated plastic was also increased, but to a lesser extent. Increased binding was observed at 0.3 ng/ml, with maximal enhancement at 33 to 100 ng/ml. Enhancement occurred within 1 min, with maximal increase after 15 min. Preincubation studies with P(Bu)2 showed that binding enhancement was entirely attributable to an effect on T cells, with no action on EC. Additive binding enhancement was seen when phorbol esters and agents that alter adhesion by acting on EC (LPS, IL 1, or IFN-gamma) were used together. The increase in T cell adhesion to EC after T cell activation may contribute to the selective emigration of activated T cells from the blood into developing inflammatory lesions. The rapid increase in binding suggests that this may be an important mechanism for immediate localization of circulating T cells, particularly sensitized T cells, in the cellular immune response, perhaps involving the activation of these cells at the endothelial blood-tissue interface.