Purification and characterization of a silica-induced bronchoalveolar lavage protein with fibroblast growth-promoting activity.

Experimentally induced silicosis provides a good model for chronic interstitial pulmonary inflammation and fibrosis. In the present study, a specific single polypeptide with an apparent molecular mass of 58,000 and a pl of 4.5 was purified and characterized from the bronchoalveolar lavage fluid of silicotic rats. The same protein was also isolated from both the extract and conditioned medium of alveolar macrophages of silicotic rats. Therefore, this protein was termed an inducible silicotic (rat) bronchoalveolar lavage protein-p58 (iSBLP58) or an inducible silicotic (rat) pulmonary macrophage factor (iSPMF-p58). iSBLP58 has been purified to homogeneity by a combination of gel permeation, Mono Q ion exchange, and reverse-phase high performance liquid chromatography. This polypeptide displayed a potent fibroblast growth-promoting activity in vitro. The sequence of the first 15 NH2-terminal amino acids was determined and was found to have high sequence homology with members of the mammalian chitinase-like protein family, which includes human cartilage gp39, mammalian oviduct-specific glycoprotein, and a secretory protein from activated mouse macrophages.