Regulation of OPN expression by inflammatory cells. (A) Schematic diagram of our in vitro assay to determine which leukocytes and which secreted factors are responsible for induction of OPN expression in fibroblasts. Western blot analyses of Swiss 3T3 fibroblast cells treated for 8 h with CM from various leukocytic cell lineages (B) or EGF, PDGF-BB, TGFβ1, TGFβ3, IL-6, or TNF-α (C) to determine which conditions lead to increased OPN expression. (D) Fibroblasts were cotreated with macrophage-CM and Gleevec, PDGF-R neutralizing antibodies (E), or wortmannin (F). (G) Swiss 3T3 fibroblasts were stimulated with 20 ng/ml PDGF-BB for the time indicated, and either immediately analyzed (left), or rinsed in fresh media and cultured for the remainder of 8 h before being analyzed for OPN expression (right).