Interaction between human neutrophils and zymosan particles: the role of opsonins and divalent cations.

Abstract

Human neutrophils were incubated with zymosan particles coated with either C3, IgG, or both. The cells formed rosettes with and ingested all 3 kinds of particle. Although C3-coated zymosan bound to about 80% of the neutrophils, the uptake of these particles was slow in comparison with IgG-coated or (C3 + IgG)-coated zymosan. All particles initiated an increase in the respiration of the cells as well as a specific release of lysosomal enzymes from the cells. IgG and C3 on zymosan reacted with different cell structures, as judged by the specific inhibition of F(ab')-anti-IgG on the IgG-mediated reactions and of F(ab') 2 -anti-C3 on the C3-mediated reactions. Moreover, trypsin treatment of the cells inhibited only the C3-mediated reactions. The binding of C3-coated zymosan and (C3 + IgG)-coated zymosan to the neutrophils was completely inhibited by addition of EDTA to or by omission of calcium and magnesium salts from the incubation medium. As a consequence, the ingestion of these particles and the stimulation of cell respiration and release of lysosomal enzymes was also strongly depressed under these conditions. In the presence of either calcium or magnesium ions, these reactions were suboptimally stimulated by zymosan coated with C3 or IgG + C3. In sharp contrast, IgG-coated zymosan and other IgG-coated material interacted with and stimulated the neutrophils in the absence as well as in the presence of divalent cations. The stimulation of neutrophil functions by phorbol myristate acetate did not require the presence of these ions either. Nonopsonized zymosan did not interact with the neutrophils during incubation in suspension. When centrifuged with the cells in a pellet, however, nonopsonized zymosan was ingested and induced a strong release of lysosomal enzymes but did not enhance the release of superoxide anions. Similar results were obtained when trypsin-treated cells were centrifuged with C3-coated zymosan. These reactions were inhibited by EDTA. The results indicate that: 1) Both IgG receptors and zymosan receptors on neutrophils mediate phagocytosis, stimulation of the respiratory burst, and initiation of lysosomal enzyme release; probably, C3 receptors only mediate binding of particles to neutrophils, a prerequisite for the interaction with the zymosan receptors. 2) Neutrophil functions are stimulated in the absence of extracellular divalent cations; therefore, influx of calcium ions into neutrophils is not required for neutrophil stimulation.