Lipopolysaccharide levels adherent to PM2.5 play an important role in particulate matter induced-immunosuppressive effects in mouse splenocytes

Epidemiological studies show that exposure to ambient particulate matter (PM) is associated with serious adverse health effects, including, but not limited to, those on the respiratory system. In the present study, we investigated the splenic response in mice administered PM of 2.5m diameter (PM2.5). Male BALB/c mice (7 or 8 weeks old) were intratracheally administered PM2.5 (0.1mg) four times, at 2week intervals, and dissected 24h after the final administration. The effect of six types of PM2.5, collected in Shenyang or Beijing (China) and Kitakyushu (Japan), on splenocytes was examined. Our results revealed a strong correlation between the levels of lipopolysaccharide (LPS), but not that of -glucan and polycyclic aromatic hydrocarbons, attached to PM2.5 and the effect of PM2.5 on cell activity. PM2.5 with a low amount of LPS (PM2.5LL) reduced splenocyte mitogen-induced proliferation and cytokine production compared with that in control mice. The suppressive effects of PM2.5LL on proliferation and interleukin-2 production in splenocytes were rescued by the antioxidant N-acetylcysteine. Expression of heme oxygenase-1 was elevated after PM2.5LL administration, particularly in CD11b(+)cells, while no elevation was observed in CD4(+), CD8(+) or B220(+) cells. Further, dissociation of the nuclear factor erythroid 2-related factor 2 from Kelch-like ECH-associating protein 1 was observed in splenocytes of PM2.5LL-administered mice. These data suggest that LPS attached to PM2.5 modulates the splenocyte immune responses to PM2.5. Exposure to ambient particulate matter (PM) is associated with serious adverse health effects. We investigated the splenic response in mice administered PM of 2.5m diameter (PM2.5) with various molecules attached, obtained from different sources. PM2.5 with a low amount of lipopolysaccharide significantly reduced splenocyte mitogen-induced proliferation and cytokine production in mice; this effect was abrogated by antioxidant treatments. Our findings indicate that lipopolysaccharide adhering to PM2.5 modulates the immune response induced by these particles in splenocytes.