Phospholipids in inflammatory synovial effusions.

The concentration of phospholipids and proteins was determined in 23 inflammatory synovial fluids obtained from human knee joints. The synovial fluid to plasma phospholipid ratio (0.48 and 0.37 at high and low inflammatory state) was lower than the value found for the total protein content (0.68 and 0.53, respectively) indicating that phospholipids were more discriminated than proteins in their transfer from plasma to the synovial space. Constant amounts of phosphatidylinositol were found in all synovial fluids, whereas trace amounts of lysophosphatidylethanolamine and phosphatidylserine were more frequent in the active inflammatory state. A decrease in the relative amounts of phosphatidylcholine and phosphatidylinositol with respect to plasma suggested the possibility of phospholipid hydrolysis in the synovial compartment. In agreement, determinations of phospholipase activity disclosed the presence of a phospholipase A2 in the fluid phase of synovial effusions. Phospholipid derivatives formed in the synovial space may thus contribute to the amplification of the inflammatory response.