Fig. 3

Mice lung tissue sections from different groups were stained by immunohistochemistry, Masson’s trichrome and Picro Sirius Red. a The blue color in Masson’s trichrome staining indicates collagen fiber, while b red color in Picro Sirius Red staining indicates collagen. These data demonstrate that PM aggravated bleomycin-induced pulmonary fibrosis. c Elevated levels of ACE2 and TMPRSS2 are observed in the bleomycin and PM group. These data indicate that PM upregulates the expression of ACE2 and TMPRSS2, mainly in areas with exacerbation of pulmonary fibrosis. d In the boxplots, quantification of pulmonary fibrosis and the levels of ACE2 and TMPRSS2. Data are shown as the median value with the interquartile range. 20X magnification. Scale bar: 50 μm. P values were determined by Kruskal-Wallis test as * p < 0.05, ** p < 0.001 and *** p < 0.001 compared with control. # p < 0.05 and ## p < 0.01 compared with bleomycin plus PM group. PM: particulate matter; ACE2: angiotensin-converting enzyme 2; TMPRSS2: transmembrane serine protease 2; Bleo:Bleomycin; Bleo+PM: Bleomycin+PM. (n = 4 per group)