Synovial fluid and peripheral blood immune complexes of patients with rheumatoid arthritis induce apoptosis in cytokine-activated chondrocytes

The destruction of cartilage is an important characteristic of rheumatoid arthritis (RA). Immune complexes (IC) are usually found in high amounts in RA synovial fluids (SF) and in the superficial layers of RA cartilage. The objective of this study was to investigate if IC have a direct influence on proliferation, survival and production of nitric oxide (NO) of cytokine-activated chondrocytes. Primary bovine chondrocytes were incubated with cytokines (huIL-1α, bovIFN-γ, huTNF-α) and IC containing precipitates of peripheral blood (PB) and/or synovial fluid (SF) of 14 RA patients, 5 osteoarthritis (OA) patients and 10 healthy age and sex-matched controls. After 48 h, chondrocyte viability, proliferation, apoptosis, NO production and oxygen radical levels were measured. Staining with May-Grünwald-Giemsa after incubation with IC of RA PB and SF, showed apoptotic chondrocytes with condensation of the nuclei. The proliferation rates of cytokine-activated chondrocytes, incubated with sera and SF IC of RA patients were significantly decreased compared to chondrocytes, incubated with sera and SF IC of OA patients and compared to sera of controls. Quantitative evaluation of apoptotic cells by annexin-V/propidium iodide and TUNEL assays revealed a significant increase after incubation with sera and SF IC of RA patients, compared to control sera and OAs sera and SF. In all TUNEL positive samples, active-caspase-3-positive cells were found. There was a significant increase of chondrocyte NO production, after incubation with SF IC of RA patients, compared to OA SF. These results support the hypothesis that IC, present in serum and SF of RA patients, have a profound influence on chondrocyte growth, NO production and apoptosis, contributing to cartilage destruction in RA.