[MOMP of Legionella inhibits phagocytosis of RAW264.7 macrophages and enhances their chemotaxis by activating NOD2/RIP2 signaling pathway].

Objective To investigate the effect of the main outer membrane protein (MOMP) of Legionella on the phagocytosis and chemotaxis of RAW264.7 macrophages and explore its mechanism. Methods MOMP and RAW264.7 macrophages were cultured in vitro. The toxicity of MOMP to RAW264.7 macrophages was detected by CCK-8 assay and 50% inhibitory concentration (IC) was determined. The RAW264.7 macrophages were treated by MOMP (1.14, 0.57, 0.28) μg/mL and the control group was established. The cells and cultivate supernatants were collected 24, 48 and 72 hours after the RAW264.7 macrophages were treated by MOMP. The phagocytic function of macrophages was detected by the neutral red phagocytosis experiment; the chemotaxis function of macrophage was examined by Transwell assay, and the levels of monocyte chemoattractant protein 1 (MCP-1) and interleukin 10 (IL-10) in cell culture supernatant monocytes were detected by ELISA. Real-time quantitative PCR was used to check the mRNA level of macrophage nucleotide-binding oligomerization domain 1 (NOD1), NOD2 and receptor-interacting protein 2 (RIP2). The protein levels of NOD1, NOD2 and RIP2 were detected by Western blot analysis. Results The IC of MOMP on RAW264.7 macrophages was 5.69 μg/mL. Compared with the control cells, MOMP treatment caused a decrease of RAW264.7 macrophage phagocytosis in a dose- and time-dependent manner. With the increase of MOMP dosage, the chemotaxis of macrophages and the secretory levels of MCP-1 and IL-10 in the cell culture supernatant increased, and peaked in 36 hours. The mRNA and protein expression levels of NOD2, RIP2 also increased, mRNA levels of NOD2 and RIP2 peaked in 12 hours, and protein levels peaked in 24 hours. Conclusion MOMP can inhibit the phagocytosis of RAW264.7 macrophages and enhance its chemotaxis function, which is related to the activation of NOD2/RIP2 signaling pathway.