Different pathways of human T-cell activation revealed by PHA-P and PHA-M.

Antigen-specific T-cell activation is mediated via the CD₃-T₁(antigen receptor) complex. and monoclonal antibodies to both CD₃ and T₁ cause a rapid rise in intracellular Ca²⁺. This calcium mobilization is not inhibited by monoclonal antibodies to CD₂. The rise in calcium mobilization induced by purified PHA (PHA-P) does not occur in a cell line which lacks CD₂ expression, and can be blocked in other I cells by anti-CD₂ antibodies. A combination of monoclonal antibodies to different epitopes of CD₂ causes calcium mobilization and mitogenesis. Reagent grade PHA (PHA- M) induces calcium moblization in cells that lack CD₂, and its effects in other T cells cannot be blocked by anti-CD₂ antibodies. The effects of PHA-P and PHA-M arc thus mediated predominantly through different activation pathways. [ABSTRACT FROM AUTHOR]