Phagocytosis and intracellular killing of Staphylococcus aureus by polymorphonuclear cells from synovial fluid of patients with rheumatoid arthritis

The phagocytosis and intracellular killing by synovial fluid (SF) polymorphonuclear cells (PMN) of 10 patients with rheumatoid arthritis was studied. PMN phagocytosis was assessed by morphologic and microbiologic methods and intracellular killing was measured independently of continuous phagocytosis of Staphylococcus aureus. Phagocytosis of S aureus by SF PMN or peripheral blood (PB) PMN was as effective in the presence of synovial fluid as in the presence of serum. On average, SF PMN ingested S aureus opsonized with synovial fluid and serum more efficiently than patient or donor PB PMN did. Enhanced ingestion of S aureus was associated with increased expression of C3 receptors on the membrane of SF PMN. In the presence of heat-inactivated synovial fluid, the capacity of SF PMN to ingest S aureus was greater than that of patient or donor PB PMN. Under these conditions, phagocytic activity was correlated with Fc receptor expression. SF PMN was found to be as active in killing S aureus as PB PMN from healthy donors.