Detection of granulocyte elastase specific IgG split products in rheumatoid synovial fluid

In vitro granulocyte elastase is known to cleave a large number of substrates e.g. complement components, fibrinogen, collagen and IgG. In vivo the enzyme is rapidly complexed by the plasma inhibitors a1proteinase inhibitor (a1PI) and a2macroglobulin. Therefore in biological fluids elastase is measured as the inactive a1PI-complex. We present a radioimmunoassay for elastase specific IgG split products as marker for the elastase activity in vivo. Elastase splits human IgG1 in Fab and Fc fragments and low molecular weight peptides. We produced specific antibodies against the elastase induced Fc fragment by immunization with an elastase generated peptide. After purification of the antibodies there is no crossreactivity with native IgG nor with similar Fc fragments produced by plasmin or papain. The elastase specific IgG split products are detected in synovial fluid samples of patients with rheumatoid arthritis. The measured concentrations are higher in the RA group than in control groups of patients with other inflammatory joint diseases.