Upregulation of platelet-derived growth factor-A and -B gene expression in alveolar macrophages of individuals with idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is characterized by accumulation of alveolar macrophages spontaneously releasing exaggerated amounts of the potent mesenchymal cell growth factor platelet-derived growth factor (PDGF). To evaluate the relative contribution of the two PDGF genes to this process, PDGF-A and -B gene transcription rates and mRNA levels were examined in normal and IPF alveolar macrophages. While normal alveolar macrophages constitutively transcribe both PDGF-A and PDGF-B genes, LPS stimulation increases the transcription of both genes more than threefold. Importantly, IPF alveolar macrophages spontaneously transcribe both genes at a rate similar to that observed for normal macrophages after in vitro stimulation. Consistent with the transcription data, normal macrophages contain mRNA for both PDGF-A and -B, but PDGF-B mRNA is 10-fold more abundant. Strikingly, in IPF, both PDGF-A and -B mRNA levels were markedly increased, with persistence of the 10-fold dominance of PDGF-B mRNA. Thus, the exaggerated release of PDGF by IPF alveolar macrophages is likely modulated by upregulated PDGF gene transcription rates and concomitantly increased mRNA levels and the persistent 10-fold excess of B greater than A PDGF mRNA suggests that the PDGF released by alveolar macrophages is likely mostly of the potent B-chain homodimeric form.