Induction of lysosomal enzyme secretion by alveolar macrophages in response to the purified complement fragments C5a and C5a des-arg.

Purified C5a and its "inactive" form, C5a des-arg, were shown to induce secretion of acid hydrolases from rabbit alveolar macrophages (AM) in a concentration-dependent manner. Secretion increased with time to 5 times above controls by 72 hr. Concentrations of these enzymes in the cell lysates did not decrease during the incubation, suggesting that synthesis of new enzyme was occurring. The lysosomal enzyme secretion was accompanied by increased pinocytosis and release of proteolytic enzymes from the macrophages. At no time was significant lactic dehydrogenase liberated, indicating that secretion was selective and not due to cell death. Data presented also suggest that C5a des-arg induced secretion from the macrophages of a chemotactic factor for neutrophils. It was concluded that C5a and C5a des-arg may play a role in lung injury by interactions with AM, inducing the secretion of acid hydrolases and proteolytic enzymes that can cause tissue damage, and by regulating the influx of other inflammatory cells into the interstitium and air spaces.