Platelet-derived growth factor (PDGF) isoforms are chemoattractants and mitogens for cells of mesenchymal origin that could be important mediators of pulmonary fibrogenesis. We have previously reported that particle-activated alveolar macrophages secrete homologues of PDGF that are composed of all three PDGF isoforms (PDGF-AA, -AB, and -BB). This mixture of macrophage-derived PDGF, once dissociated from the PDGF-alpha-macroglobulin complex, induces chemotaxis of rat lung fibroblasts (RLF) in the nanomolar range. In addition, we have reported that PDGF isoforms induce differential proliferation of RLF (PDGF-BB > PDGF-AB > PDGF-AA). In the present study, we sought to determine the relative chemotactic potency of the three PDGF isoforms and correlate these responses to the relative abundance of the two types of PDGF cell-surface receptors: PDGF-alpha receptor (PDGF-R alpha) and PDGF-beta receptor (PDGF-R beta). We also investigated the chemotactic activity of combinations of two PDGF isoforms simultaneously. Isolates of early-passage RLF were assayed for chemotaxis in 48-microwell chambers. Swiss mouse 3T3 cells were assayed in parallel as a positive control cell line for PDGF-R alpha and PDGF-R beta expression. RLF responded differentially to the PDGF isoforms: PDGF-AB and PDGF-BB were potent chemoattractants and stimulated maximal chemotactic responses between 4 and 8 ng/ml PDGF, whereas PDGF-AA elicited a weak chemotactic response that was maximally 15% of that obtained with either B-chain isoform. PDGF-AB and PDGF-BB were also the most potent chemoattractants for Swiss 3T3 cells, and their response to these B-chain isoforms was approximately 40% greater than that obtained for RLF.(ABSTRACT TRUNCATED AT 250 WORDS)