Phorbol myristate acetate--fate and usability in a human interleukin-1 assay

Phorbol myristate acetate (PMA) has been widely used to produce interleukin-1 (IL-1) from monocytes (Mø) of various species, including man. Supernatants from cultures of human Mø, stimulated with PMA, 2 X 10(-6) M, contained IL-1-like activity, as judged by their high co-mitogenic effect on mitogen-stimulated human T-cells. However, a solution of PMA in culture medium was equally as active as the supernatants. By way of 3H-PMA it was demonstrated that the IL-1-like effect of PMA-induced supernatants was non-dialyzable, was coupled to proteins with a molecular weight greater than 70,000 Dalton and could be dependent mainly upon the PMA content. Thus, previous reports dealing with basic immunological as well as immunopharmacological aspects of IL-1, must be interpreted with caution if the conclusions have been based on results obtained with crude or high molecular weight forms of PMA-induced IL-1. It could be that PMA can be used as an IL-1 inducer. However, it must first be demonstrated that PMA does not interfere with the detection of IL-1 or, if so, that PMA has been removed sufficiently from the test material to avoid interference. Secondly, the specificity of PMA with respect to IL-1 inducing effect must be demonstrated under endotoxin-free culture conditions.