Histaminase release from human granulocytes.

Abstract

Histaminase (EC 1.4.3.6), 1 of the 2 catabolic enzymes for histamine, is contained in human granulocytes. Opsonized zymosan [from Saccharomyces cerevisiae] or the calcium ionophore A-23187 induce a dose-dependent release of histaminase from human granulocytes in vitro. Release is completed within 30 min, is temperature dependent, and requires divalent cations. Opsonized zymosan-induced histaminase release was maximal in the presence of Ca and Mg; ionophore release was Mg independent. The total cellular content of histaminase could be released by opsonized zymosan and ionophore. Only 25% of the cellular .beta. glucuronidase, a lysosomal enzyme, was released after maximal stimulation with opsonized zymosan; there was minimal release of .beta. glucuronidase with ionophore. Zymosan- and ionophore-induced histaminase release was inhibited by agents that are presumed to interfere with cell metabolism and disrupt microtubules. Human granulocytes thus may modulate the effect of histamine [in hypersensitivity reactions] by releasing histaminase at a site of inflammation. Studies of granulocyte histaminase release in vitro may also provide a new model to explore granulocyte function and secretion.