Saliva initiates the formation of pro-inflammatory macrophages in vitro

Objectives: Saliva can support oral wound healing, a process that requires a temporary inflammatory reaction. We have reported previously that saliva provokes a strong inflammatory response in oral fibroblasts. Bone marrow cells also give rise to macrophages, a heterogeneous subset of cell population involved in wound healing. Lipopolysaccharide (LPS) and interleukin 4 (IL-4) induce activation of pro-(M1), and anti-(M2) inflammatory macrophages, respectively. Yet, the impact of saliva on programming bone marrow cells into either M1 or M2 macrophages remains unclear. Design: Herein, we examined whether sterile saliva affects the in vitro process of macrophage polarization based on murine bone marrow cultures and RAW264.7 mouse macrophages. Results: We report that sterile saliva, similar to lipopolysaccharides, provoked a robust activation of the M1 phenotype which is characterized by a strong increase of the respective genes IL-12 and IL-6, based on a real-time gene expression analysis, and for IL-6 with immunoassay. Arginase-1 and Ym1, both genes characteristic for the M2 phenotype, were not considerably modulated by saliva. Inhibition of TLR4 signaling with TAK-242, blocking NFKB signaling with Bay 11-7085, but also autoclaving saliva greatly reduced the development of the M1 phenotype. Conclusion: These data suggest that saliva activates the TLR4 dependent polarization into pro inflammatory M1 macrophages in vitro. (C) 2016 Elsevier Ltd. All rights reserved.