PHOSPHOLIPASE-A2 ACTIVITY ASSOCIATED WITH SYNOVIAL-FLUID CELLS

  • 1 January 1988
    • journal article
    • research article
    • Vol. 15  (5) , 791-794
Abstract
High activity of phospholipase A2 (PLA2) has been detected in synovial fluids(SF) in inflammatory arthritides. Since the source(s) of SF PLA2 has not been identified, we tested PLA2 content in SF cells obtained from 11 SF. Cell sonicates were prepared at 5 .times. 106 cells/ml. In the supernatants of the sonicated SF cells (n=11), PLA2 activity ranged from 38-755 U/ml, mean 368 .+-. 243 (SD) U/ml, compared to 5-64 U/ml, mean 31 .+-. 15 (SD) U/ml in sonicates of normal peripheral blood PMN (n=5) (p<0.0001). Spontaneous release of PLA2 from unstimulated SF cells ranged from 26-365 U/ml, mean 131 .+-. 14 (SD) U/ml (n=5), whereas spontaneous release form peripheral blood PMN was negligible. Neither 10-8 M FMLP nor 5 .times. 10-6 M dexamethasone altered extracellular PLA2 release. To assess whether PLA2 adsorbs passively to cell membranes through hydrophobic interactions, normal peripheral PMN were incubated in crude SF (n=7) with PLA2 ranging from 4,000-24,3000 U/ml, or with purified human SF PLA2 or Naja naja PLA2. We found that soluble PLA2 adsorbed to PMN membranes in a concentration dependent fashion. PLA2 activity in sonicates of PMN incubated in crude SF ranged from 185-358 U/ml compared to controls of 21-64 U/ml. Sonicates of PMN incubated with purified human SF PLA2 (5,000-30,000 U/ml) showed progressive concentration dependent increase in PLA2 from 7 .+-. 4 to 212 .+-. 11 (SD) U/ml (p < 0.001). PMN incubated with Naja naja also showed marked increase in the content of PLA2. PLA2 also adsorbed to the purified membranes of human red blood cells. We conclude that high levels of SF cell associated PLA2 may be due, at least in part, to the passive acquisition of this enzyme by adsorption to the cellular membrane.

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