The Ca2+ Dependence of Human Fcγ Receptor-initiated Phagocytosis

doi:10.1074/jbc.270.38.22301

The Ca²⁺ Dependence of Human Fcγ Receptor-initiated Phagocytosis (*)

From the (1) Cornell University Medical College, Graduate Program in Immunology, The Hospital for Special Surgery, New York, New York 10021 and the
(2) Mount Sinai School of Medicine, Department of Biochemistry, City University of New York, New York, New York 10029

^§ To whom correspondence should be addressed:
The Hospital for Special Surgery, Cornell University Medical Center, 535 E. 70th St., New York, NY 10021.
Tel.: 212-606-1214; Fax: 212-717-1192.

Abstract

Differing roles for transients in FcR-mediated phagocytosis have been suggested based on the observations that antibody-opsonized erythrocyte phagocytosis by human neutrophils shows a [Ca] dependence, while that by murine macrophages appears [Ca]-independent. To explore whether this difference might reflect different receptor isoforms or different cell types, we studied the [Ca] dependence of receptor-initiated phagocytosis by human FcRIIa and a panel of FcRIIa cytoplasmic domain mutants expressed in murine P388D1 cells and by human FcR endogenously expressed on human neutrophils and monocytes. Wild-type and point mutants of huFcRIIa stably transfected into murine P388D1 cells have different capacities to initiate a [Ca] transient, which are closely correlated with quantitative phagocytosis (r = 0.94, p < 0.0001). Phagocytosis both by huFcRIIa in P388D1 cells and by huFcRIIa endogenously expressed on neutrophils and blood monocytes shows [Ca] dependence. Phagocytosis of antibody-opsonized erythrocytes by neutrophils demonstrated greater susceptibility to [Ca] quenching compared with FcRIIa-specific internalization with E-IV.3, suggesting that the phagocytosis activating property of FcRIIIb in neutrophils also engages a [Ca]-dependent element. In contrast, phagocytosis by human FcRIa, endogenously expressed on blood monocytes, is [Ca]-independent. Despite the importance of a consensus tyrosine activation motif for both receptors, FcRIa and FcRIIa engage at least some distinct signaling elements to initiate phagocytosis. The recognition that both of the phagocytic receptors on murine macrophages and human FcRIa associate with the FcRI -chain, which contains a tyrosine activation motif distinct from that in the FcRIIa cytoplasmic domain, suggests that [Ca]-independent phagocytosis is a property associated with the utilization of -chains by FcR.

Footnotes

↵* The work was supported by United States Public Health Service Grants AR-33062 (to R. P. K.), AI-24322, and AI-24671 (to J. C. U.) and a Young Scholar Award from the New York Chapter of the Arthritis Foundation (to J. C. E.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

FcR

receptors for the Fc region of IgG

EA

bovine erythrocytes opsonized with the IgG fraction of rabbit antibovine erythrocyte polyclonal antisera

BAPTA

1,2-bis(2-aminophenoxy)ethane-N,N,N‘,N‘-tetraacetic acid

mAb

monoclonal antibody

GAM

polyclonal F(ab′) goat anti-mouse IgG

PBS

phosphate-buffered saline

PI

phagocytic index (number of erythrocytes phagocytosed per 100 phagocytes)

E

biotinylated bovine erythrocytes

E

avidin coated E

FMLP

formylmethionylleucylphenylalanine

E-IV.3 and E-22

erythrocytes coated with the anti-FcRII mAb IV.3 Fab fragments or the FcRI mAb 22 F(ab′) fragments through a biotin-avidin bridge.
- Received June 20, 1995.
- Revision received July 24, 1995.