Endogenous PAI-1 levels increase during Klebsiella pneumonia. PAI-1 protein concentrations in lung homogenates (A) and mRNA levels in lung tissues (B) were determined before and at 24 and 48 hours after intranasal (i.n.) administration of K pneumoniae. Data are means ± SE. n = 6 per group. *P < .05 versus 0 hours (uninfected mice). Murine PAI-1 in situ hybridization was performed on lung tissues before (C) and 48 hours after (D) infection. Positive signal is indicated in black. Magnification, × 100.