Study of chemotactic activity developed by neutrophils from rheumatoid arthritis patients

Neutrophils are the predominant cells accumulated in the synovial fluid (SF) of rheumatoid arthritis (RA) patients. Accumulation of neutrophils may be regarded as a possible way by which neutrophils exert cytotoxic functions. The aim of the present study was to analyze the chemotactic response of neutrophils (PMNs) isolated from the peripheral blood or SF of patients with RA by performing the chemotaxis assay, in which N-formyl-methionyl-leucyl-phenylalanine (FMLP) was used as chemotactic agent. Our results showed that FMLP induced response of peripheral blood neutrophils from 12 patients with RA was similar with the response of 15 healthy controls. A decreased chemotactic response to FMLP was, however, observed in PMNs isolated from the SF of RA patients as comlipared with peripheral blood cells. Therefore, this defective chemotactic ability of neutrophil, was inversely correlated with the number of infiltrating cells in SF. These results indicate that chemotactic ability of neutrophils may be reduced after migration to the SF. Because PMNs chemotaxis in vivo has likely occurred in the presence of serum or SF, we tried to simulate the same conditions in vitro. Therefore, we analyzed the effect of serum or SF on the RA-PMNs chemotaxis. Heat-inactivated serum produced a marked reduction of chemotactic activity developed by PMNs isolated from patients with RA. Notably, a significant increase of chemotactic activity was observed when FMLP and serum stimuli were used together, as compared with the same stimuli used alone. The results suggested that complement activation might interfere with neutrophils chemotaxis. SF amplifies the chemotactic activity of PMNs isolated from peripheral blood of RA patients, but does not affect the chemotaxis developed by PMNs isolated from SF. The data might suggest that several components of SF (IL-8, leukotrien B4, thrombin, platelet-activating factor, etc.) could serve as a potent stimulus for recruitment of neutrophils from periphery into the RA joint. In conclusion, serum or SF components seem to contribute to chemotaxis of neutrophils and play a role in differential killing of PMNs and incidence of infection.