NOD2 Mediates Intracellular Staphylococcus Aureus-induced Proinflammatory Responses Of U937 Cells And Caco-2 Cells

Objective To observe the inflammatory responses of macrophages and Caco-2 cells to Staphylococcus aureus infection. To investigate effects of NOD2 interference on inflammatory responses of macrophages and Caco-2 cells to Staphylococcus aureus.Methods Real-time PCR assay was used to detect the NOD2 mRNA expression in macrophages and Caco-2 cells during infection by S. aureus. By using ELISA assay and flow cytometry methods the cytokine secretion, NF-κB activation and cell apoptosis of the macrophages and Caco-2 cells infected by S. aureus were observed. The siRNA against NOD2 gene was synthesized and transfected into macrophages and Caco-2 cells infected with S. aureus. ELISA assay and flow cytometry methods were used to detect the effects of NOD2 gene silencing on cell phagocytosis, cytokine secretion, NF-κB activation and cell apoptosis of the macrophages and Caco-2 cells infected by S. aureus.Results It was found that S. aureus can be internalized by macrophages and Caco-2 cells. S. aureus infection could increase the expression of NOD2 mRNA, the cytokines secretion, the NF-κB activation in both macrophages and Caco-2 cells. S. aureus infection can cause apoptosis in macrophages and Caco-2 cells. NOD2 gene interference in macrophages and Caco-2 cells reduced the number of S. aureus engulfed by the cells, the levels of cytokines released and the activation of NF-κB. NOD2 gene silencing did not affect the cell apoptosis rate.Conclusion Our data suggest that the intracellular pattern recognition receptor NOD2 plays a key role in pathogen recognition, signal transduction, and NF-κB activation in the inflammatory responses of macrophages and Caco-2 cells infected by S. aureus.