Characterization of protein-antiproteinase imbalance in bronchoalveolar lavage from patients with pneumonia.

In order to clarify the mode of inactivation of alpha1-proteinase inhibitor (alpha 1-PI) in pneumonia, 21 immunocompetent patients and 19 immunocompromised patients with acute pneumonia (Groups I and II) were studied. Nine patients successfully treated for pneumonia and 10 healthy volunteers served as controls (Groups III and IV, respectively). The concentrations of alpha 1-PI, elastase and myeloperoxidase (MPO) in bronchoalveolar lavage fluid (BALF) were determined using a luminometric assay. Elastase inhibition capacity was determined using a colorimetric assay. Thus, the functional activity of alpha 1-PI was calculated. Both elastase and MPO were significantly higher in group I, when compared with the other groups. The mean concentration of alpha 1-PI was significantly higher in patients with acute pneumonia (Group I 13 mg.l-1, Group II 4.22 mg.l-1) than in Groups III and IV (2.65 and 0.33 mg.l-1, respectively), whereas, the proportion of active alpha 1-PI was significantly lower in Group I than in the other groups. Only a small proportion was present as a complex with elastase (ca. 5.9%) or in oxidised form (ca. 4.8%), 85% of alpha 1-PI was irreversibly proteolyzed. This resulted in free elastase activity in 7 of the 40 patients (18%) with acute pneumonia. We conclude that functional activity of alpha 1-PI is markedly impaired due to irreversible proteolysis in acute pneumonia, despite high immunological concentrations.