Comparative immunohistochemical study of group II (synovial-type) and group IV (cytosolic) phospholipases A2 in disc prolapse tissue.

Phospholipase A2 (PLA2) has been suggested to be present in herniated disc tissue and it could possibly be involved in sciatica/ discogenic back pain mechanisms. In the present study the occurrence of two different phospholipase A2 enzymes, (1) low molecular weight (14 kDa) group II synovial-type (sPLA2) and (2) high molecular weight (85 kDa) group IV cytosolic (cPLA2), were compared. Fifty-three disc prolapses obtained at disc operations were analyzed by immunohistochemistry, using anti-human monoclonal antibodies to sPLA2 and cPLA2, respectively. Only cell-associated (disc cells, hyaline cartilage chondrocytes) sPLA2 and cPLA2 immunoreactivity could be observed. The results showed that sPLA2 was more common (25/53, 47%) than cPLA2 (13/53, 25%). sPLA2 and cPLA2 were simultaneously present in 13 of 53 samples (25%). However, both PLA2 enzymes were predominantly present in hyaline cartilage cells (sPLA2: 16/53, cPLA2: 5/53), being less commonly observed in disc cells (sPLA2: 6/53, cPLA2: 3/53). In addition, three samples for sPLA2 and two samples for cPLA2 exhibited immunoreactivity in cartilage and disc cells simultaneously. sPLA2 was observed in no other locations, but in 3 of 53 samples cPLA2 was observed more diffusely in areas of granulation tissue, possibly in macrophages. No gender- or age-related dependence for either type of PLA2 enzyme immunoreactivity could be observed. Neither did their occurrence relate to clinical data such as straight leg raising or neurological deficit. The results do not support a major role for either of the two disc-cell-associated PLA2s in disc pathophysiology. For both enzymes, the major pool appears to reside in cartilage tissue cells, presumably in dislodged end-plate fragments. Disc cells are apparently unlikely candidates for major PLA2 storage.