role of IL-15 in inflammatory activity of patients with rheumatoid arthritis [RA]

ABSTRACT

Interleukin 15 [IL-15], a new player in the cytokine network, is produced mainly by monocytes and can be detected in the rheumatoid synovium. The aim of this study was to investigate the role of IL- 15 in patients with rheumatoid arthritis [RA]. IL-15 cytokine was measured in sera and synovial fluid [SF] of 40 patients with rheumatoid arthritis [RA] and 20 patients with osteoarthritis and only in sera of 20 healthy control using an enzyme-linked immunosorbent method. Seven American College of Rheumatology [ACR] core set measures as well as IL-15 levels were sequentially monitored at the commencement. IL-15 had been detected in sera of 16 [40%] of 40 RA patients, in two [10%] of 20 osteoarthritis [OA] patients and two [10%] of 20 healthy controls. The mean level of circulating IL-15 was significantly higher in RA patients [P < 0·001]. In SF, the mean IL-15 levels were significantly higher in RA patients [162.8 +/- 35.4] than in OA patients [32.5 +/- 5.5] [P < 0·001]. In paired samples [n=40] of sera and SF from RA patients and OA patients, IL-15 levels were higher in the SF than in sera [P < 0·001] in RA but not in OA. Rheumatoid arthritis patients with detectable IL-15 [n=25] had higher tender joint scores [P < 0·01], swollen joint scores [P < 0·001] and C-reactive protein [CRP] [P < 0·05], rheumatoid factor [P < 0.001], and long disease duration [P < 0·05] than those without [n=15]. In conclusion, IL-15 was elevated significantly in the sera and SF of patients with active rheumatoid arthritis [RA] but not on OA patients and correlated well with several parameters of RA disease activity. These observations suggest that IL-15 production may be associated with an exacerbation of RA, and then IL-15 levels could be useful to assess disease activity