To detect the disparity of three cytokines interleukin-6 (IL-6), interferon-inducible protein 10 (IP-10) and interleukin-17 (IL-17) in peripheral blood (PB) and synovial fluid (SF) of patients with juvenile idiopathic arthritis (JIA).
Serum concentrations of the three cytokines were measured in 27 patients with 13 systemic-onset JIA (sJIA), 14 polyarticular JIA (pJIA) and 28 healthy controls using enzyme-linked immunosorbent assay (ELISA). Nineteen patients with no marked arthritis symptom or only temporary arthralgia were enrolled in probable sJIA group. SF from 18 patients with 7 sJIA, 11 pJIA were examined for cytokine levels.
(1) The statistically significant difference in serum IL-6 was detected between sJIA and healthy control group [28.0(4.2-59.2) ng/L vs. 12.3 (2.1-13.8) ng/L, P < 0.05], but no significant difference between probable sJIA and healthy control group [11.8(7.7-39.2) ng/L vs. 12.3 (2.1-13.8) ng/L, P > 0.05] was found. There were statistically significant differences between sJIA group and healthy control group in serum concentrations of IL-17 [14.0(9.8-34.3) ng/L vs. 9.8 (7.9-16.2) ng/L, P < 0.05], yet compared to healthy control group, no significant difference in concentration level of IL-17 was found in pJIA Group [14.2(9.9-16.9) ng/L vs. 9.8(7.9-16.2) ng/L, P > 0.05].(2) In sJIA and pJIA SF, the median IP-10 level was significantly higher compared to respective PB levels [619.7 (160.9, 873.1) ng/L vs. 64.8 (27.4-111.9) ng/L;660.9 (401.9, 1349.8) ng/L vs. 97.4 (41.9-222.1) ng/L, P < 0.01, respectively], but there was only significant difference in IL-17 between pJIA SF and PB [22.9 (17.1, 45.8) ng/L vs. 14.2 (9.9-16.9) ng/L, P < 0.01].
IL-6 may play more important role in the pathogenesis of sJIA. Moreover, IL-6 may be the biomarker associated with arthritis in early JIA stage. Both autoinflammation and autoimmune response may be involved in the pathogenesis of sJIA. IL-17 enrichment may only occur in local joint, the levels of IL-17 in PB may not be significantly increased. The prominent expression gradient between SF and PB of IP-10 maybe the basis of performing chemotaxis and further causing joint damage.