Detection of proteases of Pseudomonas aeruginosa in immune complexes isolated from sputum of cystic fibrosis patients

Abstract

Sera and sputa of 12 cystic fibrosis patients suffering from chronic Pseudomonas aeruginosa lung infections were assayed for immune complexes using the Raji cell assay. Whereas all sera were negative, 33% of the sputa were positive for immune complexes. Sera and sputa of these patients were also assayed for antibodies against P.aeruginosa alkaline protease (AP) and elastase (Ela) and sputa for AP and Ela, using radioimmunoassays. All patients revealed antibody titers to the proteases in serum (1:5-1:1000) and eight patients had antibody titers to the proteases in sputum (1:5-1:100); all sputa were negative for AP and Ela. Sputum immune complexes and IgG were separated from whole sputum on a Protein A-Sepharose C1-4B column and treated with 0.75 M 2-mercaptoethanol and iodoacetamide after elution. After treatment, 58% of the sputa were positive for AP and/or Ela (5-200 ng/ml sputum). The present study shows that proteases of P.aeruginosa are bound in immune complexes after the initiation of the immune response to these antigens and it yields new insights into the role of these proteases in chronic lung infection in cystic fibrosis.