C1Q-BEARING IMMUNE-COMPLEXES DETECTED BY A MONOCLONAL-ANTIBODY TO HUMAN C1Q IN RHEUMATOID-ARTHRITIS SERA AND SYNOVIAL-FLUIDS

Using a monoclonal antibody directed against the C-chain of human Clq, we detected Clq-bearing immune complexes (IC) in sera and synovial fluids of rheumatoid arthritis (RA) patients. In a sandwich-ELISA, Clq-bearing IC were captured by the solid-phase monoclonal antibody and then detected with peroxidase-labeled F(ab')2-antibodies to either human IgG or IgM. The results of this assay were compared to an ELISA-modification of the Clq-solid-phase binding assay (Clq-SPBA). Clq-bearing IC were detected in 81.1% of RA-sera and the 65.2% of RA-synovial fluids. IgG as well as IgM was present in 72.6% of the sera and 70% of the synovial fluids which were positive in both assays. Most RA sera that were only positive for Clq-bearing IC, contained IgG alone (81.5%). The corresponding synovial fluids showed IgG alone (53%) or both IgG and IgM (41.1%). IgM alone (25%) could be detected in sera, e.g. in juvenile forms of RA. The levels of IC were higher in synovial fluid than in paired serum. In comparison to normal human serum (NHS) and patients with osteoarthritis, complement activity (CH50 titers) and Clq-values in patients with RA were frequently elevated. Since the formation of Clq-bearing IC is an indicator for the classical complement pathway activation, an assay with monoclonal anti-Clq antibody may be a useful tool in the diagnosis of rheumatoid diseases.