Specific Modulation of Complement-dependent Human Granulocyte Function by Imidazole Acetic Acid

Because imidazole acetic acid (IAA), a product of histamine catabolism was shown to inhibit histaminase release from human polymorphonuclear leukocytes (PMNs), the effect of this compound on other neutrophil functions was investigated. IAA at concentrations of 10(-10) or more inhibited histaminase release induced by particle-bound C3b, the larger fragment of the activated form of the third component of complement. Release of histaminase induced by aggregated IgG, phorbal myristate acetate (PMA), formyl-methionyl-leucyl-phenylalanine (FMLP) and calcium ionophore was not affected by IAA. In addition IAA had no effect on release of beta-glucuronidase, myeloperoxidase, and lysozyme or on phagocytosis and superoxide generation. IAA did modestly inhibit neutrophil chemotaxis. These findings suggest a highly specific modulating effect of the histamine catabolite IAA on complement-mediated PMN function.