Complement deposition on immune complexes reduces the frequencies of metabolic, proteolytic, and superoxide oscillations of migrating neutrophils

Abstract

Neutrophils exhibit intrinsic sinusoidal metabolite concentration oscillations of 3 min in resting cells and an additional approximately 10- or 20-s oscillation in migrating/adhering cells. To better understand immune complex (IC)-mediated leukocyte activation, we have studied neutrophil metabolic oscillations in the presence of ICs either with or without fixed complement. Using a microscope photometer we quantitated NAD(P)H autofluorescence oscillations. Cells exposed to ICs exhibited metabolic oscillation periods of approximately 12 s in the absence of complement and approximately 22 s in the presence of complement opsonization. To determine if the effects could be associated with C3 deposition, we used ICs opsonized with only C3 or only C1 and C4. Untreated ICs, heat-inactivated complement-treated ICs, and C1,C4-treated ICs trigger rapid metabolic oscillations, as do fMLP and yeast; in contrast, ICs treated with full complement or C3 alone did not affect NAD(P)H oscillations in comparison to controls. The induction of higher frequency (approximately 10 s) NAD(P)H oscillations by ICs could be blocked by addition of anti-FcgammaRII, but not FcgammaRIII mAb fragments, suggesting the participation of FcgammaRII in cellular metabolic responses to ICs. Parallel changes in the frequencies of oxidant release and pericellular proteolysis were found for all of these stimuli. Thus, immune complex composition affects both intracellular metabolic signals and extracellular functional oscillations. We suggest that complement attenuates the phlogistic potential of ICs by reducing the frequency of cytoplasmic NAD(P)H oscillations.