Synovial type (group II) phospholipase A2 in cartilage

Phospholipase A2 (PLA2) was produced in E. coli by a recombinant technique using a synthetic gene coding for PLA2 found in synovial fluid (SF) of patients suffering from rheumatoid arthritis (RA). Polyclonal antibodies were produced against the recombinant synovial type PLA2 (syn-PLA2) in a rabbit. The IgG fraction of the antiserum was isolated and the specificity was tested by immunoblotting. The antiserum detected a protein with an apparent molecular weight of 15 kDa in extracts of cartilage, but did not react with PLA2 isolated from human pancreas or ascitic fluid. In immunohistochemistry, the anti-syn-PLA2 antibody decorated chondrocytes and matrix of articular, laryngeal and auricular cartilage, but did not decorate synovial tissue or its contained inflammatory cells in RA or other human tissues tested (pancreas, liver, thyroid, tonsil, lung, nasal polyp, skin, placenta, myometrium, bone). The results show that syn-PLA2 is present both in articular and extraarticular cartilage and support the view that PLA2 found in SF might originate from chondrocytes, and not from synovial lining or inflammatory cells.