The effect of non-inflamed synovial fluid on neutrophil function in vitro

In neutrophils preincubated with non-inflamed synovial fluid, opsonized zymosan-induced O2- production was increased by 232.7 +/- 19.1% and degranulation induced by zymosan or phorbol myristate acetate was increased by 152.8 +/- 21.8% and 217.4 +/- 26.3 respectively. Unstimulated neutrophils were not directly activated by the fluid, nor did it affect their chemotactic response. The activity was not abolished by heat (56 degrees C, 30 min, or 100 degrees C, 3 min) or by treatment with trypsin or hyaluronidase. The activity was not present in the serum albumin-bound lipid extract of the synovial fluid. Thus, this activity may represent a heat- and trypsin-resistant factor which is neither a complement component nor hyaluronic acid. It is proposed that this synovial fluid factor plays a role in increasing the neutrophil killing potential during the inflammatory process.