Dissociation of phagocytosis, metabolic stimulation and lysosomal enzyme release in human leukocytes

Abstract

In this paper studies are reported concerning the relationship between particle binding to the plasma membrane of human polymorphonuclear leukocytes (PMN's), phagocytosis, generation of oxidative metabolites, and the release of lysosomal enzymes by these cells. Superoxide (O2-) generation by, and lysosomal enzyme release from, normal PMN's and cytochalasin B-treated cells were measured. We have found that neither phagocytosis nor lysosomal degranulation are prerequisites for enhanced O2- generation. Cytochalasin B-treated PMN's, incapable of ingesting particles but still able to bind particles to membrane receptors, generated enhanced amounts of O2- when treated with serum-treated zymosan (STZ), a C3b receptor stimulus, or with aggregated IgG (agg IgG), an Fc receptor stimulus. Moreover, the soluble stimulators complement component C5a, phorbol myristate acetate (PMA), and calcium ions in the presence of the ionophore A23187, also increased the O2- production of these cells. In all cases a time and dose-dependent stimulation was found of both the O2- generation and the lysosomal enzyme release, but there was no correlation between ability of any stimulus to provoke enzyme release and its ability to stimulate O2- generation. When PMN's were preincubated with 5 X 10(-4) M hydrocortisone-Na-succinate, lysosomal enzyme exocytosis with the immune reactants was inhibited 16-35%. Hydrocortisone also inhibited O2- generation, except when STZ was used as the stimulus. Thus, in the case of stimulation of functional processes of PMN's via the C3b receptor, hydrocortisone inhibits membrane fusion without interfering with one of the early biochemical events (O2-production).