A human fibroblast cell line (WI-38) derived from normal embryonic lung tissue was obtained from ATCC, Rockville, MD. Immortalized PAR-1 deficient (PAR-1-/-) and PAR-2 deficient (PAR-2 -/-) murine lung myofibroblasts were derived from PAR-11 and PAR-22 knock-out mice. Immortalized wild-type murine lung myofibroblasts were derived from the same strain of mouse that was used to generate the knock-out mice. PAR-1 -/- cells, which lack all functional PARs, were transfected with human PAR-1 or PAR-2 cDNA using a mammalian expression vector encoding hygromycin resistance gene (pcDNA3.1). All cell lines were grown in Dulbecco''s modified Eagle medium (GIBCO BRL Life Technologies, Grand Island, NY) supplemented with 10% heat-inactivated fetal bovine serum (Cellgro, Herndon, VA), 1% penicillin and streptomycin (Bio Whittaker, Walkersville, MD), and 1% L-glutamine (Bio Whittaker). The medium was supplemented with hygromycin B (250 μg/ml) when transfected cell lines were cultured.