Human group II phospholipase A2. Characterization of monoclonal antibodies and immunochemical quantitation of the protein in synovial fluid.

Murine monoclonal and rabbit polyclonal antibodies were generated against human group II phospholipase A2 (PLA2) in order to study the role of this enzyme in inflammatory disease, the source of its synthesis, and the interaction of PLA2 with its substrate. Monoclonal antibody PLA187 exhibits potent inhibitory activity toward human PLA2 using autoclaved E. coli membranes as the substrate. Three other monoclonal antibodies (PLA184, PLA185, and PLA186) also inhibit enzyme activity, but with about 50-fold less potency. Based on the results of double-antibody competition experiments and enzyme inhibition profiles, PLA184 and PLA185 appear to recognize the same epitope. Monoclonal antibody PLA186 recognizes an epitope which is spatially distinct from that recognized by PLA184/185. The results also suggest that the epitope recognized by PLA187 may overlap with both epitopes recognized by PLA186 and PLA184/185. A double-antibody sandwich ELISA was developed using a combination of PLA185 and rabbit polyclonal antibody against PLA2. The ELISA provides a sensitive and quantitative method for monitoring specifically group II PLA2 in various biological sources, independent of factors which may affect enzyme activity. We have utilized this assay to quantitate PLA2 levels in synovial fluid from the joints of individuals with rheumatoid arthritis as well as from non-arthritic joints. Our results indicate that elevated levels of group II PLA2 in synovial fluid are not necessarily associated with arthritis.