Phorbol myristate acetate-induced macrophage aggregation.

Phorbol myristate acetate (PMA) at nanomole concentrations induces a rapid aggregation of guinea pig macrophages. This aggregation is dependent on extracellular Mg2+ (but not Ca2+) for its development. Additionally, it is inhibited by some agents which also inhibit aggregation induced by lymphokines and the ionophore A23187. Although the mechanism of aggregation has not been determined, it does not appear to be related to either arachidonic acid metabolites or products of the respiratory burst. In this respect, it resembles the PMA-induced aggregation of neutrophils.