INCREASED EXPRESSION OF IL-15 IN THE SYNOVIUM OF PATIENTS WITH RHEUMATOID-ARTHRITIS COMPARED WITH PATIENTS WITH YERSINIA-INDUCED ARTHRITIS AND OSTEOARTHRITIS

Recently, a new player in the cytokine network has been described that is produced by monocytes and can be detected in the rheumatoid synovi um: interleukin-15 (IL-15). Since this cytokine may play a role in the accumulation and activation of T-cells, B-cells, and natural killer ( NK) cells characteristic of synovial tissue (ST) from patients with rh eumatoid arthritis (RA), the expression of IL-15 was studied in ST fro m RA patients in comparison with ST from patients with reactive arthri tis (ReA) and osteoarthritis (OA) and the phenotype of IL-15-positive cells was determined. IL-15 expression was investigated by immunohisto chemical analysis of ST from ten patients with RA, ten patients with Y ersinia enterocolitica-induced ReA, and nine patients with OA. The imm unohistological findings were quantified and the results obtained in t he different patient groups were compared. To determine the phenotype of IL-15-expressing cells, double-labelling immunofluorescence was per formed. The expression of IL-15 was significantly higher in ST from pa tients with RA than in ST from patients with ReA or OA. In double-labe l experiments, co-expression was observed with markers for macrophages , T-cells, and NK cells. The composition of the cellular infiltrate in the synovium of patients with RA might be partly explained by the spe cific increase in expression of IL-15 in rheumatoid ST. It can be spec ulated that IL-15 production by inflammatory cells other than macropha ges may occur in the rheumatoid synovium. (C) 1997 by John Wiley & Son s, Ltd.