Extracellular NAD is a regulator for FcγR-mediated phagocytosis in murine macrophages

NAD is available in the extracellular environment and elicits immune modulation such as T cell apoptosis by being used as the substrate of cell surface ADP-ribosyl transferase. However, it is unclear whether extracellular NAD affects function of macrophages expressing cell surface ADP-ribosyl transferase. Here we show that extracellular NAD enhances Fcγ receptor (FcγR)-mediated phagocytosis in J774A.1 macrophages via the conversion into cyclic ADP-ribose (cADPR), a potent calcium mobilizer, by CD38, an ADP-ribosyl cyclase. Extracellular NAD increased the phagocytosis of IgG-coated sheep red blood cells (IgG-SRBC) in J774A.1 macrophages, which was completely abolished by pretreatment of 8-bromo-cADPR, an antagonist of cADPR, or CD38 knockdown. Extracellular NAD increased basal intracellular Ca²⁺ concentration, which also was abolished by pretreatment of 8-bromo-cADPR or CD38 knockdown. Moreover, the chelation of intracellular calcium abolished NAD-induced enhancement of phagocytosis of IgG-SRBC. Our results suggest that extracellular NAD act as a regulator for FcγR-mediated phagocytosis in macrophages.