A controlled biochemical and immunohistochemical study of human synovial-type (Group II) phospholipase A(2) and inflammatory cells in macroscopically normal, degenerated, and herniated human lumbar disc tissues

Study Design. Group II phospholipase A(2) enzyme activity was studied biochemically and immunohistochemically in tissue samples from disc prolapses, degenerated discs, and macroscopically normal discs. In parallel, phospholipase A(2) and inflammatory cells were studied by indirect immunocytochemistry. Objectives. To compare phospholipase A(2) activity in normal discs and abnormal discs by an identical assay for phospholipase A(2), and to compare the occurrence of inflammatory cells with phospholipase A(2) activity and immunoreactivity. Summary of Background Data. It has been suggested that a high phospholipase A(2) enzyme activity in herniated disc tissue could be significant in abnormal states such as sciatica and discogenic pain. No comparison between healthy disc tissue and samples of abnormal discs (degenerated or herniated) has been carried out. In particular, an identical assay for phospholipase A(2) for such tissue samples, supported by immunohistochemical staining data, has never been applied in parallel to normal and abnormal disc tissue, and neither have such results been compared with the demonstration of inflammatory cells. Methods. Group II phospholipase A(2) enzyme activity was determined, in parallel, using an identical assay for tissue samples from 11 macroscopically normal discs, 33 disc herniations, and six discs showing degeneration by discography. For determination of phospholipase A(2) enzyme activity, a radioassay using 1-palmitoyl-2- (1-C-14)linoleoyl-L-3-phosphatidylethanolamine as the phospholipid substrate was used. Total tissue DNA as an estimate of total tissue cell number was measured in parallel with phospholipase A(2) activity. All tissue samples also were studied by indirect immunocytochemistry, locating phospholipase A(2) and T and B lymphocytes. Results. Neither degenerated nor nor herniated disc tissue samples demonstrated a higher phospholipase A(2) activity than control disc tissue samples. Average phospholipase A(2) activity was actually higher in the control samples than in herniated disc samples (Mann-Whitney test, P < 0.001), possibly a result of a higher total DNA (P < 0.005). The observed level of phospholipase A(2) activity was lower than that of inflammatory human synovial fluid. Neither was there marked immunoreactivity for phospholipase A(2), which was observed in chondrocytes in areas of cartilage and occasional disc cells, supporting the biochemical results. Lymphocytes were more numerous only in herniated disc samples (15%), and their presence showed little overlap with phospholipase A(2) immunoreactivity. Conclusions. Synovial-type (Group II) phospholipase A(2) enzyme activity is not particularly high in disc tissue and does not appear to be higher in herniated or degenerated discs than control disc tissue. Immunoreactivity to phospholipase A(2) is seen only occasionally and is strong only when cartilage tissue is present. Neither are inflammatory lymphocytes commonly observed.