BAFF induces IL-6 production by monocytes through a BAFF receptor and promotes IgG production by B cells in patients with primary Sjögren's syndrome. (CCR3P.210)

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Abstract Backgrounds and Objectives: We have found that the elevated expression of BAFF receptor (BR3) on monocytes is involved in activation of monocytes to promote IL-6 production in patients with primary Sjögren's syndrome (pSS). In addition, it is well known that pSS is often accompanied by hypergammaglobulinemia (HγG). In our present study, we investigated the possible involvement of monocytes in the development of HγG. Methods: Peripheral monocytes were cultured in vitro with or without peripheral B cells and stimulated with soluble BAFF (sBAFF). The amounts of IL-6 and IgG in the culture supernatants were measured by ELISA. FACS analysis of whole blood samples was employed to analyze the expression of BR3. Results: The serum level of IgG and the proportion of BR3-positive monocytes (BR3+/CD14+) were elevated in pSS patients as compared to those in normal individuals. Remarkably, the BR3+/CD14+ ratio was positively and significantly correlated with the serum IgG level. In addition, the ratio was positively and significantly correlated with the amount of IL-6 produced by pSS monocytes stimulated with sBAFF. Stimulation of co-culture of B cells and monocytes with sBAFF drastically enhanced IgG production by B cells. Conclusions: Our data collectively suggest that the abnormal expression of BR3 on monocytes is responsible for the overproduction of IgG by B cells in pSS patients.