Cytokines produced by inflammatory cells play a pivotal role in synovial inflammation and joint destruction in rheumatoid arthritis. To investigate the influence of pro-inflammatory cytokines (IL-1α, IL-6, TNF-α, IFN-γ) and subsequently the possible beneficial role of an anti-inflammatory cytokine (IL-4) on chondrocyte viability (necrosis/apoptosis), proliferation and nitric oxide (NO) production.

Primary bovine chondrocytes were cultured until monolayers were obtained. Cells were incubated with cytokines (IL-1α, IFN-γ, TNF-α, IL-4, IL-6) at 0.1, 1, 10 and 100ng/mL. After 48h, the viability of the chondrocytes was measured flow cytometrically with propidium iodide. Proliferation was determined by the incorporation of tritiated thymidine. The morphology of the chondrocytes, including presence of apoptotic nuclei, was evaluated by a May-Grünwald–Giemsa staining. In addition, the number of apoptotic chondrocytes was detected flow cytometrically with a TUNEL technique and annexin-V/propidium iodide staining. NO production was evaluated using a spectrophotometric assay, based upon the Griess reaction.

The viability and proliferation of bovine chondrocytes decreased after incubation with 100ng/mL IL-1α, TNF-α or IFN-γ. In contrast, incubation of chondrocytes with IL-4 or IL-6 had no influence on the viability or the proliferation of cells. IL-1α was able to enhance NO production in a dose dependent manner. IFN-γ and TNF-α induced NO production only at the highest concentration (100ng/mL), whereas IL-4 and IL-6 did not. There was a dose dependent increase in apoptosis of bovine chondrocytes cultured in the presence of IL-1α and TNF-α. This effect could not be prevented by preincubation with IL-4. Preincubation with IL-4 diminished IL-1α and TNF-α induced NO production and increased proliferation of chondrocytes. In an additional experiment, incubation of human chondrocytes with anti-Fas did not induce apoptosis as measured by annexin-V/propidium iodide staining.

Pro-inflammatory cytokines are able to induce apoptosis, whereas IL-4 as an anti-inflammatory cytokine can inhibit the effect of IL-1α and TNF-α on NO production and proliferation of bovine chondrocytes.