Response of neutrophils to stimulus infusion: Differential sensitivity of cytoskeletal activation and oxidant production

Abstract

The responses of human neutrophils to N-formyl peptides were studied under conditions where ligand binding was controlled by infusing a cell suspension with the peptide over a time period comparable to the normal half-time for binding. Receptor occupancy was measured in real time with a fluorescently labeled peptide using flow cytometry. This binding was approximated by a simple reversible model using typical on (7 x 108 M- min-1) and off (0.35/min) rate constants and the infusion rates (0.02-0.2 nM/min). Under conditions of stimulus infusion intracellular calcium elevation, superoxide generation, and right angle light scatter and F-actin formation were measured. As the infusion rate was decreased into the range of 10 pM/min, lowering the rate of increase of receptor occupancy to ~0.5% per min, the calcium and right angle light scatter responses elongated in time and decreased in magnitude. Superoxide generation decreased below infusion rates of ~100 pM/min (occupancy increasing at a rate in the range of 5% per min). This behavior could contribute to differnces between chemotactic responses, which appear to require low rates of receptor occupany over long periods, and bactericidal or inflammatory responses (free radical generation and degranulation), which require bursts of occupancy of several percent of the receptors.