Abstract Recently, it has become evident that stimulated phosphoinositide (PI) hydrolysis plays a crucial role in early T lymphocyte activation. We have investigated the effects of the nonmitogenic lectin wheat germ agglutinin (WGA) on several parameters associated with PI hydrolysis in human T cells. It was found that WGA was as effective as anti-T3 antibody and PHA in producing a rise in cytosolic free Ca++ ((Ca++)i) in blood T cells and in cells of the T cell line CCRF-CEM. It was inferred that identical cells within the blood T cell preparation responded to each of the three agents, refuting the contention that WGA only stimulated a subfraction of circulating mature T lymphocytes. WGA-induced, but not PHA-induced rises in (Ca++)i could be blocked completely by N-acetyl-D-glucosamine, demonstrating that the sugar-binding characteristics of the lectin dictate its action on T lymphocytes. Anti-T3 antibody, PHA, and WGA all initiated inositol phosphate formation in blood T cells, indicating that each of the agents stimulated PI hydrolysis. The combination of WGA with nonmitogenic amounts of phorbol-12-myristate-13-acetate resulted in strong mitogenicity. It is concluded that WGA, like anti-T3 antibody and PHA, is a pan-T activator of PI hydrolysis.
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