NEW PROCEDURE FOR THE DETECTION OF COMPLEMENT DEFICIENCY BY ELISA - ANALYSIS OF ACTIVATION PATHWAYS AND CIRCUMVENTION OF RHEUMATOID-FACTOR INFLUENCE

A procedure using enzyme-linked immunosorbent assays for the assessmen t of complement function has been evaluated. The sera investigated wer e incubated in microtiter plates with solid-phase complement activator s. Human polyclonal IgG or monoclonal IgM were used for classical acti vation pathway assays and Salmonella typhosa lipopolysaccharide (LPS) for alternative activation pathway assays. The analysis focussed on de position of C9 and properdin as detected with enzyme-conjugated antibo dies. In an attempt to avoid spurious results due to rheumatoid factor s in patient sera, monoclonal mouse and chicken antibodies were unsucc essfully tested as indicator reagents in the assay with solid-phase Ig G. However, the use of solid-phase IgM as an activator completely circ umvented the influence of rheumatoid factors. With solid-phase IgG or IgM, properdin deposition occurred in the absence of factor D. A combi nation of assays is suggested for diagnostic purposes: IgM-coated plat es with detection of bound C9 and properdin for the classical pathway and LPS-coated plates with detection of bound properdin for the altern ative pathway. The procedure distingished between defects of the class ical activation pathway (C1, C4, C2), the alternative activation pathw ay (C3, factor B, factor D, properdin) and the terminal components (C5 -C9). This analytical approach may be useful for detection of inherite d complement deficiency and the assessment of complement function in a cquired complement deficiency states.