MiR‐16 regulates mouse peritoneal macrophage polarization and affects T‐cell activation

MiR‐16 is a tumour suppressor that is down‐regulated in certain human cancers. However, little is known on its activity in other cell types. In this study, we examined the biological significance and underlying mechanisms of miR‐16 on macrophage polarization and subsequent T‐cell activation. Mouse peritoneal macrophages were isolated and induced to undergo either M1 polarization with 100 ng/ml of interferon‐γ and 20 ng/ml of lipopolysaccharide, or M2 polarization with 20 ng/ml of interleukin ( IL )‐4. The identity of polarized macrophages was determined by profiling cell‐surface markers by flow cytometry and cytokine production by ELISA . Macrophages were infected with lentivirus‐expressing miR‐16 to assess the effects of miR‐16. Effects on macrophage–T cell interactions were analysed by co‐culturing purified CD 4 + T cells with miR‐16‐expressing peritoneal macrophages, and measuring activation marker CD 69 by flow cytometry and cytokine secretion by ELISA . Bioinformatics analysis was applied to search for potential miR‐16 targets and understand its underlying mechanisms. MiR‐16‐induced M1 differentiation of mouse peritoneal macrophages from either the basal M0‐ or M2‐polarized state is indicated by the significant up‐regulation of M1 marker CD 16/32, repression of M2 marker CD 206 and Dectin‐1, and increased secretion of M1 cytokine IL ‐12 and nitric oxide. Consistently, miR‐16‐expressing macrophages stimulate the activation of purified CD 4 + T cells. Mechanistically, miR‐16 significantly down‐regulates the expression of PD ‐L1, a critical immune suppressor that controls macrophage–T cell interaction and T‐cell activation. MiR‐16 plays an important role in shifting macrophage polarization from M2 to M1 status, and functionally activating CD 4 + T cells. This effect is potentially mediated through the down‐regulation of immune suppressor PD ‐L1.