Increased serum levels of interleukin 10 in Sjogren's syndrome; Correlation with increased IgG1

Objective. To determine levels of interleukin 10 (IL-10) and IgG subclasses in serum from 53 patients with primary Sjogren's syndrome (SS). Methods. Serum levels of IL-10 were measured using specific sandwich ELISA in 25 patients with "definite" SS, 28 with "possible" SS, and 32 healthy co ntrols. Interferon-gamma (IFN-gamma) and transforming growth factor-beta 1 (TGF-beta 1) were also measured by immunoassays. Immunoglobulin classes, Ig G subclasses, and C-reactive protein were measured by nephelometry. Results, Circulating IL-10 was elevated in 25 patients. The increase reache d significance in the group with possible SS (p = 0.03) versus controls. In the group with definite SS, IL-10 level was correlated with IgG1 level (p = 0.01, r = 0.67) and with focus score (p = 0.01). IFN-gamma was undetectab le in most patients. TGF-beta 1 was higher (not significantly) in possible SS than in definite SS. Conclusion. IL-10 is increased in SS and may account for the overproduction of IgG1 in the syndrome. High IL-10 in the absence of increased IgG1 in po ssible SS suggests that IL-10 may be necessary but not sufficient for IgG1 overproduction and that other factors are involved. Whereas the correlation of IL-10 level with focus score was expected, it is intriguing that IL-10 was more frequently increased in the incomplete (possible) form of SS than the complete (definite) form. Elevated IL-10 may characterize the lower sta ge of eccrine dysfunction and perhaps contributes to limiting its severity.