Establishment and clinical application of an assay for the activity of circulating immune complexes using human O-erythrocytes as an indicator system

Abstract

ObjectiveTo develop a suitable clinical laboratory assay for detecting the activity of circulating immune complexes (CICs) that activate complement (ACIC). MethodsCICs measured in serum were initially used to activate complement, and the remaining complement was activated through sensitized human O-erythrocytes. ACIC was quantified by the degree of hemolysis. Each serum sample was tested for ten consecutive days to determine its stability. Reference ranges are suggested. ACIC was measured in both healthy individuals and patients with autoimmune diseases as well. ResultsThe OD values of the hemolysis degree index were inversely proportional to ACIC (r = -0.986, P = 0.002). A pooled serum was used to eliminate interference and optimize the experiment. The hemolysis degree (HD) was used to indicate the detection result. HD = (detection value OD/negative value OD)*100. Both the intra-batch and the inter-batch results showed good stability with a CV of 6.5% and 8.1%, respectively. HD differences between males and females were significant (P = 0.015) while the normal distribution for both genders was conformed. The HD recommended reference range for men is 56–88 while for women is 51–86. Serum HD of healthy subjects and autoimmune disease patients showed a significant difference (P = 0.001). Autoimmune disease patients have lower HD which was a result of having stronger ACIC. ConclusionThe ACIC assay while utilizing human O-erythrocytes as an indicator system is sensitive and accurate, and has potential in clinical applications.