Immunoglobulins from patients with ecGVHD immunoprecipitate and phosphorylate PDGF receptor. (A) Fα and F−/− lysates were immunoprecipitated with IgG purified from extensive cGVHD patients (ecGVHD) and patients without GVHD (No GVHD). The filters were developed with specific antibodies against the PDGFR α and β subunits (WB). Total lysates indicate immunoblots of total proteins. Representative results from 1 of 3 experiments are shown. (B) Normal human fibroblasts were stimulated with different concentrations of IgG from patients with ecGVHD (15 minutes), PDGF (15 ng/mL for 15 minutes), or grown in 0.2% fetal calf serum. Cell lysates were immunoprecipitated with a polyclonal antibody against PDGFR (subunit α), and the immunoblots were developed with a specific antibody against phosphorylated tyrosine. FCS indicates fetal calf serum.