Bombesin-like peptides in alveolar macrophage: Increased release in pulmonary inflammation and fibrosis

Rat bronchoalveolar cells (99% alveolar macrophages (AM)) were obtained by bronchoalveolar lavage and examined for their content of bombesin-like immunoreactivity (BLI) by radioimmunoassay (RIA), immunocytochemistry and high performance liquid chromatography (HPLC) analysis. Rat AM contained and released in their culture media significant levels of BLI, the major molecular form corresponding to gastrin-releasing peptide (GRP). Release of BLI by AM was not affected by in vitro activation of AM with lipopolysaccharide and muramyl dipeptide, but was enhanced following in vivo treatment with inflammatory agents. AM from animals with inflammation and fibrosis released higher levels of BLI than controls at 3 and 6 weeks after treatment. These changes were correlated with a significant increase in the proportion of low density mature AM as determined by Percoll density gradient fractionation. Together, our data indicate that increased release of BLI by AM may be related to AM maturation and support a role for bombesin-like peptides as modulator(s) of inflammatory reactions.