A NOVEL ELISA FOR THE EVALUATION OF THE CLASSICAL PATHWAY OF COMPLEMENT

Assessment of the overall function of the classical pathway of complem ent is traditionally performed by the hemolytic titration assay CH50. In the present study, we established a novel method for the quantitati on of complement activity by measuring the deposition of C1q, C4, C3 a nd C9 on solid-phase IgM by an enzyme-linked immunosorbent assay (ELIS A). Using the CH50 method as the reference, C9 deposition values displ ayed a sensitivity of 96.3% and a specificity of 99.4% in sera from pa tients with a variety of diseases. For C3, the sensitivity was 91.3% a nd the specificity 100%, for C4, the values were 95% and 100%, and for Clq, the corresponding values were 52.9% and 98.9%. A close correlati on was found between CH50 values below 30 U/ml and the deposition of C 9 (r = 0.92), C3 (r = 0.91) and C4 (r = 0.92). In two patients with po stinfectious glomerulonephritis normal C4 and Clq deposition was accom panied by decreased C3 and C9 deposition reflecting complement activat ion predominantly through the alternative pathway. In contrast, in two patients with complete C2 deficiency the deposition of C3 and C9 was undetectable together with normal C4 deposition values. Furthermore, i n two patients with hereditary C1-inhibitor deficiency distinctly incr eased Clq deposition was accompanied by decreased C4 deposition values . In conclusion, the determination of complement deposition by ELISA r epresents a novel, quantitative method for the evaluation of complemen t activity. The measurement of C9 deposition alone or in combination w ith further complement proteins makes this ELISA a valuable tool for a ssessing the degree and level of complement consumption as well as loc alizing the missing protein in the case of complement deficiencies. (C ) 1998 Elsevier Science B.V.