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NLRC5, the largest member of the Nod‐like receptor (NLR) family, has been reported to play a pivotal role in regulating inflammatory responses. Recent evidence suggests that NLRC5 participates in Toll‐like receptor (TLR) signaling pathways and negatively modulates nuclear factor‐κB (NF‐κB) activation. In this study, we investigated the interaction between NLRC5 and TLR2 in the NF‐κB inflammatory signaling pathway and the involvement of NLRC5 in TLR2‐mediated allergic airway inflammation. We knocked down TLR2 and NLRC5, respectively in the RAW264.7 macrophage cell line by small interfering RNA (siRNA) and then stimulated the knockdown cells with lipoteichoic acid (LTA). In comparison with the negative siRNA group, the level of NLRC5 expression was lower in the TLR2 siRNA group, with a reduction in the NF‐κB‐related inflammatory response. Conversely, in the NLRC5 knockdown cells, after LTA‐treated the level of TLR2 expression did not change but the expression levels of both NF‐κB pp65 and NLRP3 increased remarkably. Thus, we hypothesize that NLRC5 participates in the LTA‐induced inflammatory signaling pathway and regulates the inflammation via TLR2/NF‐κB. Similarly, in subsequent in vivo experiments, we demonstrated that the expression level of NLRC5 was significantly increased in the ovalbumin‐induced allergic airway inflammation. However, this effect disappeared in TLR2‐deficient (TLR2 −/−) mice and was accompanied by reduced levels of NF‐κB expression and airway inflammation. In conclusion, NLRC5 negatively regulates LTA‐induced inflammatory response via a TLR2/NF‐κB pathway in macrophages and also participates in TLR2‐mediated allergic airway inflammation. [ABSTRACT FROM AUTHOR]

Mer receptor tyrosine kinase (MerTK) expressed in macrophages is essential for phagocytosis of apoptotic cells. Here, we investigate whether MerTK is involved in the phagocytosis of Staphylococcus aureus ( S. aureus) and regulation of staphylococcal lipoteichoic acid (LTA)-induced inflammatory response in macrophages. We found that stimulating RAW264.7 macrophages with S. aureus activated multiple signaling pathways including toll-like receptor 2 (TLR2), scavenger receptor A (SR-A), and MerTK. Meanwhile, S. aureus stimulation also induced activation of proteins focal adhesion kinase (FAK) and Rac1, which are related to phagocytosis. Pretreatment with a specific Mer-blocking antibody significantly inhibited S. aureus-induced phosphorylation of MerTK, while it had no effect on S. aureus-induced activation of FAK and Rac1. Moreover, by confocal laser microscope, we observed that the antibody blockade of MerTK had little impact on the phagocytosis of S. aureus by RAW264.7 macrophages. Additionally, pretreatment with this antibody further promoted LTA-induced phosphorylation of nuclear factor κB (NF-κB) p65 subunit and production of pro-inflammatory cytokines, such as TNF-α, IL-6, IL-1β, and macrophage inflammatory protein-2 (MIP-2). Collectively, these results suggest that MerTK does not play an essential role in the phagocytosis of S. aureus but attenuates inflammation induced by staphylococcal LTA through blocking NF-κB activation. [ABSTRACT FROM AUTHOR]