Inflammation after blood injection into a synovial-like space is a result of the cellular component rather than the plasma.

The rat subcutaneous air pouch, a model for a synovial-like space, has been used to study the effect of blood as an inducer of inflammation. Six-day-old pouches were injected with autologous whole blood, with plasma or with blood cell pellets. We found significantly more inflammation and proliferation of pouch lining in pouches injected with whole blood or with the blood cell pellets than with the plasma. After the injection of blood or the cell component, large numbers of hemoglobin crystals and lipid droplets were found in the pouch fluid and were associated with erosions of the pouch membrane.