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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 × 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 ≥ 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.