ExtractThe present study using immunologic methodology confirms previous observations from this laboratory of an absence of a protease component with arginine esterase activity in plasma of patients with cystic fibrosis. In this study, the pooled plasma from control individuals was activated and partially purified after adsorption on columns of soybean trypsin inhibitor conjugated to Sepharose 4B followed by elution with benzamidine. The fraction was further purified by isoelectrofocusing on polyacrylamide gels. Proteins around the pI range of 5.5 were eluted and utilized to prepare an antiserum. Immunoelectrophoresis of activated plasma samples from control subjects and patients with cystic fibrosis was performed utilizing the antiserum. In controls, four precipitin arcs with residual esterase activity were observed, whereas only three were seen in plasma from patients with cystic fibrosis. Double gel diffusion experiments using specific antisera ruled out the presence of trypsin, chymotrypsin, plasminogen, prothrombin, C1 esterase,α1-trypsin inhibitor, and inter-α-trypsin inhibitor in the concentrated benzamidine eluate. The antisera toα2-macroglobulin gave an immunoprecipitate which was readily stained for proteolytic activity. On immunoelectrophoresis, theα2-macroglobulin precipitin band corresponded to the band absent in plasma of patients with cystic fibrosis. In contrast, theα2-macroglobulin levels were similar in plasma of control subjects and patients with cystic fibrosis. Using the antiserum to the protein fraction with a pI of 5.5 in cross immunoelectrophoresis, three “rockets” with proteolytic activity could be demonstrated in control plasma. One specific enzyme-active “rocket” was absent in plasma of patients with cystic fibrosis. In a double blind study of 15 control samples and 15 samples from patients with cystic fibrosis, a specific “rocket” was shown to be present in 13 control samples and absent in 14 cystic fibrosis samples.α2-Macroglobulin was determined by both an immunologic procedure and by its trypsin binding (trypsin protein esterase concentration). The ratio of the immunologic assay to the biologic activity assay was 90 for the normal plasma samples and only 65 for cystic fibrosis samples.SpeculationThe absentα2-macroglobulin-protease complex in plasma of patients with cystic fibrosis might reflect a molecular defect in either a protease with arginine esterase activity or within theα2-macroglobulin molecule.