IL-6 knockout alleviates inflammatory response and improve acute lung injury via regulating macrophage polarization in sepsis

Abstract Background Sepsis is a fatal disease with a high rate of morbidity and mortality, during which acute lung injury is the earliest and most serious complication. Macrophage plays a crucial role in the initiation and progress of sepsis. This study meant to explore the effect of IL-6 knockout in CLP induced sepsis. Methods In this study, cecal ligation and puncture (CLP) was performed on wildtype and interleukin 6 (IL-6) knockout C57 mice. General condition and death rate of sepsis mice were observed. organ samples (lungs, livers, kidneys and hearts) and serum were collected for histology observation and inflammatory cytokine detection. Lung tissue injury detection were conducted via lung injury score, wet/dry ration and protein concentrations measurement of Bronchoalveolar lavage fluid (BALF). In in vivo studies, RAW264.7 macrophages were transfected with IL-6 specific siRNA and treated with LPS. After exposed to IL-6 specific siRNA and LPS, expression of inflammatory cytokines interleukin 1 (IL-1), tumor necrosis factor-α (TNF-α), IL-6 and interleukin 10 (IL-10) were detected by RT-qPCR, concentration of IL-1 and TNF-α in culture supernatant were detected by ELISA and M1 and M2 markers were detected by western blot and flow cytometry. Results We constructed CLP induced sepsis models and found that inhibition of IL-6 could improve general condition and death rate of sepsis mice. Mice in IL-6 knockout group display improved tissue damage, especially in the lung tissue. IL-6 knockout relieved inflammatory cytokines storm in both serum and bronchoalveolar lavage fluid while polarized macrophage to an anti-inflammatory M2 phenotype. In cell model, inhibition of IL-6 could alleviate LPS induced expression of inflammatory cytokines IL-1, TNF-α, and IL-6 in macrophages. Western blot and Flow cytometry results indicated that expression of M1 markers (iNOS and CD86) in LPS stimulated macrophages were significantly declined while M2 (Arg-1 and CD206) were enhanced when expression of IL-6 was blocked. Conclusion Inhibition of IL-6 alleviated LPS induced inflammation and exerted protective effect in sepsis via regulating macrophage function and polarization.