Fcgamma-receptors induce Mac-1 (CD11b/CD18) mobilization and accumulation in the phagocytic cup for optimal phagocytosis.
Functional interactions between Fcgamma-receptors (FcgammaR) and the beta2 integrin Mac-1 (CD11b/CD18) have been described, but the molecular basis of this relationship remains unclear. Although the glycosylphosphatidylinositol-linked receptor FcgammaRIIIB of human neutrophils is constitutively associated with Mac-1, we found no evidence for direct physical association between Mac-1 and the FcgammaR of mouse macrophages, which are transmembrane proteins. Nevertheless, Mac-1 accumulated in the phagocytic cup following engagement of FcgammaR by IgG-opsonized particles. Blocking the CD18 chains of beta2 integrins by using specific antibodies reduced Mac-1 accumulation in the cup. These antibodies or the addition of the recombinant CD11b I-domain inhibited the ingestion of IgG-opsonized particles. FcgammaR cross-linking stimulated cell adhesion to surfaces coated with Mac-1 ligands and in addition enabled macrophages to bind C3bi-opsonized particles, indicating that FcgammaR-derived signals induce activation of Mac-1. Measurements of fluorescence recovery after photobleaching revealed that whereas most (>80%) of Mac-1 is immobile in resting cells, stimulation of FcgammaR markedly increases the mobile fraction of the integrin. Activation of Mac-1 by FcgammaR required the activity of Src family tyrosine kinases, phosphatidylinositol 3-kinase and phospholipase C, with the release of diacylglycerol and stimulation of protein kinase C. Because elevated cytosolic Ca2+ was not required, we suggest that novel protein kinase C isoforms are involved in Mac-1 activation. These results suggest that FcgammaR stimulation promotes Mac-1 clustering into high avidity complexes in phagocytic cups by releasing the integrin from cytoskeletal constraints and enhancing its lateral diffusion. FcgammaR can enhance host defense by activating Mac-1 (and possibly other integrins), having a synergistic effect on pathogen engulfment and promoting the adherence of phagocytes at sites of infection.
Jongstra-Bilen
Jenny
J
Cell Biology Program, Hospital for Sick Children and the Department of Biochemistry, University of Toronto, Toronto, Ontario M5G 1X8, Canada.
Harrison
Rene
R
Grinstein
Sergio
S
D000818:Animals; D015703:Antigens, CD / Q000737:chemistry*; D039481:CD11b Antigen / Q000378:metabolism*; D018821:CD18 Antigens / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism; D005434:Flow Cytometry; D058851:GPI-Linked Proteins; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D006801:Humans; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009504:Neutrophils / Q000378:metabolism; D010587:Phagocytosis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms; D017452:Receptors, IgG / Q000737:chemistry*; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism
D015703:Antigens, CD; D039481:CD11b Antigen; D018821:CD18 Antigens; D004075:Diglycerides; C428200:FCGR3B protein, human; D058851:GPI-Linked Proteins; D017261:Glycosylphosphatidylinositols; D020033:Protein Isoforms; D017452:Receptors, IgG; D011994:Recombinant Proteins; D019869:Phosphatidylinositol 3-Kinases; D010738:Type C Phospholipases; D002118:Calcium