Determination of the complement component C2 by ELISA in human serum and bronchoalveolar lavage fluids

In order to measure the concentration of the human complement component C2 in various biological fluids, an enzyme linked immunosorbent assay (ELISA) was developed. This assay was highly sensitive and allowed to detect as few as 400 pg of C2 in a sample volume of 150 microliters (i.e. 2.6 ng/ml). This is a 10- to 15-fold increase in sensitivity with regard to the conventional hemolytic test. As assessed by an immunoblot analysis, our anti-C2 antiserum was able to detect native C2 as well as the cleavage fragments C2a and C2b generated upon complement activation through the classical pathway. Thus, complement activation involving the classical pathway can easily be evidenced by comparing functional (hemolytic) and immunochemical (ELISA) C2 assays which respectively do not and do reveal activated C2. When C2 was assayed in either normal human serum or bronchoalveolar fluids, in both ELISA and hemolytic tests, a highly significant correlation was observed between the two assays (P less than or equal to 0.01). The specific C2 activity (i.e. functional hemolytic activity/ng C2 assayed in ELISA) was higher in serum than in bronchoalveolar lavage fluids from both normal volunteers and patients with pulmonary diseases.