Phospholipases D1 and D2 coordinately regulate macrophage phagocytosis.
Phagocytosis is a fundamental feature of the innate immune system, required for antimicrobial defense, resolution of inflammation, and tissue remodeling. Furthermore, phagocytosis is coupled to a diverse range of cytotoxic effector mechanisms, including the respiratory burst, secretion of inflammatory mediators and Ag presentation. Phospholipase D (PLD) has been linked to the regulation of phagocytosis and subsequent effector responses, but the identity of the PLD isoform(s) involved and the molecular mechanisms of activation are unknown. We used primary human macrophages and human THP-1 promonocytes to characterize the role of PLD in phagocytosis. Macrophages, THP-1 cells, and other human myelomonocytic cells expressed both PLD1 and PLD2 proteins. Phagocytosis of complement-opsonized zymosan was associated with stimulation of the activity of both PLD1 and PLD2, as demonstrated by a novel immunoprecipitation-in vitro PLD assay. Transfection of dominant-negative PLD1 or PLD2 each inhibited the extent of phagocytosis (by 55-65%), and their combined effects were additive (reduction of 91%). PLD1 and PLD2 exhibited distinct localizations in resting macrophages and those undergoing phagocytosis, and only PLD1 localized to the phagosome membrane. The COS-7 monkey fibroblast cell line, which has been used as a heterologous system for the analysis of receptor-mediated phagocytosis, expressed PLD2 but not PLD1. These data support a model in which macrophage phagocytosis is coordinately regulated by both PLD1 and PLD2, with isoform-specific localization. Human myelomonocytic cell lines accurately model PLD-dependent signal transduction events required for phagocytosis, but the heterologous COS cell system does not.
Iyer
Shankar S
SS
Inflammation Program, Division of Infectious Diseases, Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City 52241, USA.
Barton
James A
JA
Bourgoin
Sylvain
S
Kusner
David J
DJ
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D042381:Granulocyte Precursor Cells / Q000276:immunology*; D006801:Humans; D008262:Macrophage Activation / Q000276:immunology; D008264:Macrophages / Q000201:enzymology* / Q000276:immunology; D018613:Microscopy, Confocal; D018448:Models, Immunological; D010587:Phagocytosis / Q000276:immunology*; D010739:Phospholipase D / Q000276:immunology*; D011233:Precipitin Tests; D020033:Protein Isoforms / Q000276:immunology; D014162:Transfection
D020033:Protein Isoforms; C105606:phospholipase D2; D010739:Phospholipase D; C106801:phospholipase D1