To determine whether blood and synovial fluid (SF) immune complexes (IC) of patients with rheumatoid arthritis (RA) influence the production of nitric oxide (NO) and growth and viability of chondrocytes.
IC were precipitated and IgM and IgG were determined in the precipitates by ELISA and nephelometry, respectively. Primary cultures of bovine articular chondrocytes were incubated with the IC precipitates. After 48 h NO was determined as nitrite. After 7 days, growth was determined by incorporation of tritiated thymidine and viability was detected by neutral red uptake.
Patient sera were positive in 8/12 for IgM IC and 9/12 for IgG IC, and 1/8 control sera was slightly positive for IgM IC. Seven of 12 SF samples were IgM IC and 10/12 IgG IC positive. With and without additional interleukin 1alpha (IL-1alpha) stimulation, NO production by chondrocytes was significantly higher with SF IC precipitates than with control serum precipitates (p = 0.03, p = 0.04, respectively). NO production by chondrocytes that were not stimulated with IL-1alpha was significantly increased with SF IC precipitates compared to RA serum IC precipitates (p = 0.03). SF IC significantly inhibited growth compared to control serum precipitates (p = 0.04) and RA serum IC (p = 0.012). Neutral red uptake by chondrocytes was significantly decreased when incubated with RA serum IC in comparison with control serum IC (p = 0.012) and SF IC (p = 0.006). With and without additional IL-1alpha stimulation, NO production by chondrocytes after incubation with SF derived IC was positively correlated to the Ritchie score (r = 0.8, r = 0.7, respectively) and the number of swollen joints (r = 0.8, r = 0.6, respectively).
These results support the hypothesis that, especially in active RA, SF derived IC stimulate NO production and inhibit chondrocyte growth.