To study the changes of serum interleukin-15 (IL-15) levels and the expression of CD4(+)T (T-helper lymphocyte) subsets CD4(+)CD45RA(+) and CD4(+)CD45RO(+) in peripheral blood of children with juvenile rheumatoid arthritis (JRA).
The serum concentration of IL-15 was detected using ELISA in 39 children with JRA. The expressions of CD4(+)CD45RA(+)T and CD4(+)CD45RO(+)T in peripheral blood were detected by flow cytometry in 24 out of the 39 patients with JRA. Twenty-six age and sex-matched healthy children were used as the Control group.
The mean serum IL-15 level in JRA patients was significantly higher than that in controls (1.37 +/- 0.98 pg/mL vs 0.96 +/- 0.41 pg/mL, P <0.05). Among the 39 JRA patients, the serum IL-15 level in 17 patients with systemic JRA increased remarkably (P < 0.01), but not in patients with the other two types of JRA, the oligoarthritis and polyarthritis (n=13, n=9, respectively), compared with that in controls. The mean serum IL-15 level of the JRA patients was significantly reduced after conventional treatment (P < 0.01). The serum IL-15 level in JRA patients positively correlated with white blood cell count (r=0.347, P <0.05) and C reactive protein (r=0.452, P < 0.01) but not with the erythrocyte sedimentation rate. The patients with high serum IL-15 levels (> or = medium level 1.73 pg/mL) had higher expression of CD4(+)CD45RO(+)T than those with low serum IL-15 levels (< medium level) (16.29 +/- 5.46% vs 11.75 +/- 3.15 %, P < 0.05).
The serum IL-15 levels in JRA patients increased significantly. An increased IL-15 level can transform CD45RA into CD45RO in peripheral blood of patients with JRA, and then result in T lymphocyte activation and mediate the immunopathological impairment. IL-15 may be used a marker for the evaluation of severity of JRA.