Secretion of Alpha1 -Proteinase Inhibitor by Cultured Rat Alveolar Macrophages1–3

Alpha1 proteinase inhibitor, metabolically labeled with 35S1 was detected in concentrated culture medium of rat alveolar macrophages by immunoelectrophoresis autoradiography. The metabolically labeled macrophage alpha1proteinase inhibitor had the same electrophoretic mobility as did pure rat serum alpha^proteinase inhibitor. Moreover, monospecific antiserum to rat serum alpha1proteinase inhibitor precipitated a 35S-labeled protein from macrophage culture supernates, and this protein was shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis to have a molecular weight close to that of rat serum alpha^proteinase inhibitor. Cycloheximide (an inhibitor of protein synthesis) at a concentration of 0.50 μg/m\, inhibited secretion of labeled inhibitor. Thus, cultured rat alveolar macrophages secrete detectable concentrations of a proteinase inhibitor believed to play a major role in lung defense.