PDGFB and pulmonary arterial hypertension: They found that after hypoxic exposure, Pdgfb mRNA was up-regulated in mouse macrophages and Pdgfb expression was down-regulated in mouse macrophages carrying hypoxia-inducible factor 1α (hif-1α), hypoxia-inducible factor 2α (hif-2α) or the Pdgfb allele LysM-Cre and protected from distal muscularization and PAH.