ACTIVATION OF ALVEOLAR MACROPHAGES BY NATIVE AND SYNTHETIC COLLAGEN-LIKE POLYPEPTIDES

Interstitial connective tissue fragments are known to be chemotactic for neutrophils and these have been implicated in mediating the migration of inflammatory cells to the lung following injury. In the present studies, we determined if degradation products of collagen also induced chemotaxis and functional activation of alveolar macrophages. For these studies, we used bovine dermal collagen digested with bacterial collagenase or cyanogen bromide and small molecular weight synthetic polypeptides containing proline (Pro), glycine (Gly), and hydroxyproline (Hyp). We found that collagenase or cyanogen bromide digests of native collagen, as well as synthetic polypeptides containing Pro and Gly in the pentameric (Pro-Pro-Gly), form, were potent chemoattractants for rat alveolar macrophages inducing migration in the nanomolar concentration range. We also found that native and synthetic collagen peptides stimulated the release of superoxide anion and hydrogen peroxide, as well as elastase and gelatinase release from alveolar macrophages. These effects were dose and time dependent, reaching a maximum after 72 h with 0.1 to 1 muM peptides. In contrast to chemotaxis, synthetic peptides containing Hyp also stimulated reactive oxygen intermediate and elastase release from the cells. Although the pentameric and decameric forms of the synthetic peptides were equally effective in stimulating elastase release, (Pro-Pro-Gly)5 and (Pro-Hyp-Gly) 5 peptides were more active in inducing a respiratory burst. We also determined if alveolar macrophages were activated for cytotoxicity by collagen peptides. Treatment of the macrophages with native collagen digests or (Pro-Pro-Gly)5 was found to induce cytotoxicity of these cells towards both transformed and nontransformed rat-derived targets. As observed with chemotaxis, peptides containing Hyp had no effect on cytotoxicity. These data provide additional evidence that collagen degradation products participate in the pathogenesis of inflammatory lung disease and suggest that the structural requirements for activating alveolar macrophage receptors for chemotaxis, oxidative metabolism, and hydrolytic enzyme release by collagen peptides are distinct.