Exposure duration of ambient fine particulate matter determines the polarization of macrophages.

Ambient fine particulate matter (FPM) promotes airway inflammation and aggravates respiratory and cardiovascular diseases. Macrophage polarization plays an essential role in FPM-induced inflammation and tissue repair. The balance of pro-inflammatory M1-type and anti-inflammatory M2-type macrophages determines the fate of tissues and is involved in the pathogenesis of various FPM-induced diseases. The mechanism of macrophage polarization induced by FPM is still not fully understood. Here, we explored the effect of ambient FPM exposure duration on the polarization of peritoneal macrophages. Mice were exposed to concentrated ambient FPM for different duration. Markers of M1-type macrophage and M2-type macrophage in peritoneal macrophages were detected. We found that macrophage polarization was affected by FPM both in vitro and in vivo. Acute FPM stimulation in vitro and short-term concentrated ambient FPM exposure in vivo promoted the expression of NLRP3 and NOS2 and inhibited the expression of ARG1 and CD206. With the extension of concentrated ambient FPM exposure time, ARG1 was gradually up-regulated, and NLRP3 was gradually down-regulated. These results indicate that FPM exposure duration interferes with macrophage polarization. This may provide new insight into the treatment of patients exposed to FPM.