Quantification of fibrocytes. Fibrocytes, defined as CD45 and collagen I (Col-I) double-positive cells, were counted from 5 random high-power fields (HPFs) per lung section obtained on day 14 of saline and bleomycin (BLM) treatment with or without pirfenidone at × 40 magnification. Fibrocytes in the specimens on day 14 of BLM treatment were increased compared with those in control mice and were significantly attenuated by pirfenidone administration (*P = 0.0097). Data are presented as means ± standard error from 4 separate experiments. n = 5 in each group. PFD, pirfenidone.