Stimulatory antibodies to PDGFR from patients with ecGVHD induce type I collagen. Type I collagen gene expression by normal human fibroblasts after incubation with 0.2% fetal calf serum for 48 hours, PDGF (15 ng/mL for 15 minutes), extensive cGVHD IgG (ecGVHD; 200 μg/mL for 15 minutes), IgG from patients without GVHD (No GVHD IgG; 200 μg/mL for 15 minutes) in the presence and absence of AG1296 (2 μM for 1 hour before treatment), N-acetylcysteine (NAC; 20 mM for 1 hour before treatment), and farnesyl protein transferase inhibitor FTI-277 (20 μM for 2 hours before treatment). Real-time quantitative (RT)-PCR of the transcripts of genes encoding the α1 and α2 chain of type I collagen was performed as described in “Material and methods.”