Expression of interferon β in synovial tissue from patients with rheumatoid arthritis:: comparison with patients with osteoarthritis and reactive arthritis

Background: IFN beta may have immunomodulatory effects in rheumatoid arthritis (RA) and its increased production in RA synovium may be a reactive attempt to inhibit inflammation. Objective: To determine the expression of IFN beta in the synovial tissue of patients with RA, osteoarthritis, and reactive arthritis. Methods: Synovial biopsy specimens were obtained by arthroscopy from patients with RA and disease controls for immunohistological analysis using a monoclonal antibody specific for IFN beta. Bound antibody was detected by an immunoperoxidase method. Stained sections were evaluated by computer assisted image analysis. Double stainings were performed with antibodies to detect CD55 positive fibroblast-like synoviocytes (FLS), CD68 positive macrophages, and CD83 positive dendritic cells (DCs) coexpressing IFN beta. Results: IFN beta protein was abundantly expressed in the synovium of patients with RA. Digital image analysis showed a significant increase in the mean integrated optical density for IFN beta expression in RA synovial tissue compared with disease controls. Specific up regulation of IFN beta expression was also seen when the results were controlled for cell numbers. Phenotypic analysis showed that FLS, especially, but also macrophages and DCs may express IFN beta in RA synovial tissue. Conclusions: The increased expression of IFN beta in RA synovium suggests activation of an immunomodulatory mechanism that could inhibit synovial inflammation.