N-Formylmethionyl-leucyl-phenylalanine: Different releasing effects on human neutrophils and rat mast cells

N-Formylmethionyl-leucyl-phenylalanine (FMLP) is a synthetic chemotactic peptide which induced β-glucuronidase and lysozyme release from human neutrophils treated with cytochalasin B. FMLP-releasing effects were rapid and dose dependent. Unlike other secretagogues of neutrophils (e.g., zymosan and immune complexes), FMLP secretory activity was not modulated by acetylcholine, which by itself did not release lysosomal enzymes from human neutrophils. Isolated rat mast cells did not respond to FMLP, which has been demonstrated to release histamine from human neutrophils. Two markers of rat mast cell secretory granules, histamine and β-glucuronidase, were assayed, but the results were negative for both. In the same experimental conditions, 48/80 released histamine and the enzyme: the ratio of the net percentage release of β-glucuronidase to the net percentage release of histamine was ∼-0.4.