NADPH oxidase 2 inhibitor diphenyleneiodonium enhances ROS-independent bacterial phagocytosis in murine macrophages via activation of the calcium-mediated p38 MAPK signaling pathway.

Activation of NADPH oxidase 2 (NOX2) triggers reactive oxygen species (ROS) generation, both of which are essential for robust microbial clearance by phagocytes. However, it is unknown whether inhibition of NOX2 activation or ROS generation affects cellular phagocytosis. Here, we found that the classic NOX2 inhibitor diphenyleneiodonium (DPI) induced uptake of E. coli by murine peritoneal macrophages through enhancing phagocytosis, and this effect was temperature-sensitive and attenuated by cytochalasin D as well as chemical inhibition of Syk and PLCγ, two downstream kinases involved in actin polymerization during phagocytosis. DPI also decreased the production of TNF-α and IL-6 resulting from E. coli stimulation. The DPI-induced enhancement of phagocytosis was independent of NOX2 inhibition or ROS generation but depended on increased intracellular calcium and activation of the p38 MAPK signaling pathway. Furthermore, DPI enhanced bacterial elimination and ameliorated inflammation in E. coli-infected mice, leading to improved survival. Our results demonstrate that DPI facilitates ROS-independent bacterial phagocytosis by macrophages through activation of calcium and p38 MAPK signaling pathways.