Surface expression of Fc gamma receptor III (CD16) on chemoattractant-stimulated neutrophils is determined by both surface shedding and translocation from intracellular storage compartments.

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Abstract
Stimulation of neutrophils (PMN) with chemoattractants markedly increases surface expression of several membrane proteins, including the complement receptors, CR1 and CR3, by translocation from intracellular storage compartments to the cell surface. When we stimulated freshly-isolated PMN with FMLP, we observed little net change in surface Fc gamma receptor (R) III expression. However, if elastase was first used to cleave most (85-90%) of the Fc gamma R III from the PMN surface, subsequent treatment with FMLP induced a rapid renewal of surface Fc gamma R III, achieving levels of approximately 70% of that originally present on the cell surface after 15 min, suggesting translocation of intracellular receptors. This was confirmed by demonstrating concomitant depletion of greater than 80% of the intracellular Fc gamma R III. Studies of density gradient fractions of N2-cavitated PMN indicated at least two distinct intracellular membrane fractions that contain Fc gamma R III. Shedding of Fc gamma R III induced by FMLP was about half-maximal by 15 min and nearly complete by 60 min. Stoichiometric assessment of FMLP-induced changes in PMN surface and intracellular Fc gamma R III showed a marked depletion in intracellular Fc gamma R III, little net change in surface Fc gamma R III, and a large overall loss of total cell Fc gamma R III that could be attributed to shedding. We conclude that stimulation by chemoattractants causes a rapid translocation of intracellular Fc gamma R III to the PMN surface that is roughly balanced by the concomitant FMLP-induced shedding of this receptor.