Effects Of Lactic Acid On Macrophage Phenotype And Function

Background and Objects:Tumor cells produced amount of lactic acid via Aerobic glycolysis. Lactic acid, a fundamental trait and essential component of tumor microenvironment (TME), exerts profound and unique effect on tumor cells and immune cells such as T cells, dendritic cells and macrophages. Clinical data also unraveled a close relevance between lactic acid and tumor occurrence and prognosis. Macrophage, an important component of innate immunity, can be activated by different stimuli and differentiate into two phenotypes:M1and M2. M1activated by Th1cytokines can kill pathogens and tumor cells; but, Th2cytokines activated macrophage turn into M2phenotype. Tumor associated macrophages (TAM) manifest M2macrophage characteristics which promote tumor growth and progress, aid the tumor angiogenesis and suppress anti-tumor immunity. However, the mechanism contributing to the shift from M1to M2in TME is still unclear. Therefore, our study focus on demonstrating the role that lactic acid in TME plays in regulating macrophages’ phenotype and function.Methods:Firstly, The group of Balb/c mice was challenged by4T1breast tumor cells with the mammary gland injection. The tumor tissues were harvested at different time points and lactic acid concentrations in tumor tissue were detected. Then, the expression of M1and M2markers in the macrophage cell line RAW264.7treated with different doses of lactic acid were detected by RT-PCR, Real-time PCR, FACS or Western blot. The mouse cytokine array panel was used to evaluate the release of cytokines in the supernatant of RAW cells treated with15mmol/L lactic acid. Phagocytosis and antigen presenting function were evaluated by using FACS. The expression of NFκB P50, P65, phosphorylated NFκB P65, Stat3or Fral in RAW cells treated with15mmol/L lactic acid was detected by RT-PCR or Western blot.Results:The results revealed that lactic acid concentration in mouse breast tumor tissue was higher than that in normal breast tissue. The expression of M2markers CD206and Arg1in RAW cells treated by15mmol/L lactic acid were up-regulated, whereas the expression of M1marker NOS2was down-regulated. Furthermore, M1cytokines secretions of RAW cells treated with15mmol/L lactic acid were down-regulated. The phagocytosis was not affected by lactic acid, but down-regulated the expression of the antigen presenting and co-stimulatory molecules were determined in RAW cells treated with15mmol/L lactic acid. Moreover, phosphorylated NFκB P65was decreased, but Fral was up-regulated in RAW cells treated by15mmol/L lactic acid.Conclusion:Our study demonstrated that the Macrophages with M2phenotype can be induced by lactic acid in tumor microenvironment, and the antigen presenting function of RAW cells was impaired by lactic acid. The transcription factor NFκB P50/P65and Fral might be involved in the phenotype polarization of macrophage. These results suggested that lactic acid promotes tumor associated macrophage shift to M2phenotype, thus modulating anti-tumor immunity.