NEUTROPHIL FUNCTIONAL-RESPONSES DEPEND ON IMMUNE-COMPLEX VALENCY

Ligand-induced cross-linking of Fc gamma receptors (Fc gamma R) on neu trophils plays a significant role in their stimulation, shown here by contrasting the responses induced by low valency immune complexes (LIC s) and high valency immune complexes (HICs) and by cross-linking LICs in situ (L/Ab) after their addition to the cells. Multiparameter flow cytometry was used to measure immune complex (IC)-elicited changes in cytoplasmic Ca2+ concentration and initiation of the oxidative burst s imultaneously in the same cell and to correlate these with Fc gamma R occupancy. We have previously shown that subpopulations of neutrophils respond maximally to subsaturating concentrations of HIC; saturating dosages stimulate the entire population. This discrepancy was not due to differenees in receptor occupancy. The magnitude of the transient C a2+ increase was independent of the dose of HIC but depended on the do se when an LIC was used. As shown here, WAb cross-linking elicited Ca2 + responses similar to those observed in HIC-stimulated cells. In cont rast, LIC elicited only minimal intracellular Delta pH and no oxidativ e burst or membrane potential changes at all unless Fc gamma R was cro ss-linked, accomplished by HIC or by L/Ab. However, azurophilic degran ulation, as determined by elastase release, was not observed in cells stimulated by the in situ cross-linking method, whereas the HIC prepar ation triggered azurophilic degranulation. Thus, some Fc gamma R-media ted neutrophil effector functions such as azurophilic degranulation an d oxidative burst initiation have an absolute requirement for Fc gamma R crosslinking, whereas signaling functions such as changes in membra ne potential, intracellular pH, and intracellular Ca2+ concentration c an occur, albeit more slowly and to a lesser extent, if single Fc gamm a R are occupied.