AUTOMATED HOMOGENEOUS LIPOSOME-BASED ASSAY SYSTEM FOR TOTAL COMPLEMENT ACTIVITY

We developed an automated homogeneous immunoassay, based on immune lys is of dinitrophenyl (DNP)-labeled liposomes, for measuring total compl ement activity. Liposome lysis caused by complement activity was detec ted spectrophotometrically from entrapped glucose-6-phosphate dehydrog enase activity. Complement activity in human sera was quantified by co mparison with a calibration curve. For ease of application to fully au tomated routine clinical analyzers, we adopted a two-reagent system, o ne reagent containing a homogeneous population of small DNP-labeled li posomes and one containing antibody/substrate. This system required ca libration only once a week. Within-run and between-run CVs were 0.4-1. 3% (n = 10) and 1.8-4.7% (n = 10), respectively. Serum results were li near upon dilution (with saline) over a twofold range. Bilirubin, hemo globin, Intrafat(R), and serum proteins such as rheumatoid factor, M p rotein, IgG, and IgA did not affect the assay results. The results (y) correlated well with those from a hemolytic complement activity test (x): y = 1.05x - 1.14, r = 0.92, on 66 samples in the range <10->50 kU /L. This method should therefore be of great use for the determination of complement activity.