FRI0274 Elevated reactivity of cd38highigd+ b cells against baff contributes to igg overproduction in patients with primary sjÖgren’s syndrome
Authors: E. Ishioka-Takei, K. Yoshimoto, K. Suzuki, H. Yasuoka, K. Yamaoka, T. Takeuchi
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Primary Sjögren's syndrome (pSS) is often accompanied by hypergammaglobulinemia and production of autoantibodies, such as anti-Ro/SSA and anti-La/SSB antibodies. These serological aberrations suggest that abnormally activated B cells play a key role in the pathogenesis of pSS. We have previously reported that the proportion of peripheral CD38<sup>high</sup>IgD<sup>+</sup> B cells among CD19<sup>+</sup> B cells is significantly elevated in pSS patients and positively correlated with serum anti-Ro/SSA, anti-La/SSB titer, total IgG, and the European League against Rheumatism (EULAR) Primary Sjögren's syndrome disease activity index (ESSDAI). B cell activating factor belonging to TNF family (BAFF) is a well known cytokine which promotes differentiation, proliferation and survival of B cells. It has been reported that serum BAFF level is increased in pSS patients compared to HC and that BAFF is also highly expressed in salivary glands. Based on these background, it is conceivable that BAFF plays a pivotal role in the pathogenesis of pSS. <h3>Objectives</h3> To elucidate the involvement of BAFF in IgG overproduction in pSS. <h3>Methods</h3> Peripheral CD19<sup>+</sup> B cells were prepared from pSS patients (n=16) and gender-matched HC (n=10) by using CD19-microbeads. The cells were stimulated <i>in vitro</i> with an anti-IgM antibody, recombinant human CD40 ligand and recombinant human IL-4 ('multiple stimulation') with or without recombinant human soluble BAFF (rhsBAFF) for 96 hours. The amount of IgG produced by the cells in the culture supernatants was measured by ELISA. The proportion of B cell subsets, characterised by anti-CD19, anti-IgD and anti-CD38 antibodies, and the expression level of a BAFF receptor (BR3) in the subsets were analysed by FACS. Disease activities of the pSS patients were quantified based on the ESSDAI scores. The serological data of the patients were collected by clinical records. <h3>Results</h3> IgG production by CD19<sup>+</sup> B cells <i>in vitro</i> upon multiple stimulation was significantly increased in pSS patients as compared to HC (p=0.015). Notably, the IgG production was further enhanced by the addition of rhsBAFF to the culture, and that enhancement was significantly higher in pSS patients than HC (p=0.011). Moreover, the proportion of CD38<sup>high</sup>IgD<sup>+</sup> B cells among CD19<sup>+</sup> B cells was significantly and positively correlated with not only serum IgG level (p&lt;0.0001), but also the amount of IgG produced <i>in vitro</i> by the multiple stimulated CD19<sup>+</sup> B cells (p=0.042). The mean fluorescence intensity of BR3 expression in CD38<sup>high</sup>IgD<sup>+</sup> B cells was significantly higher in pSS patients than HC (p=0.029), whereas no significant difference was observed between pSS and HC for total CD19<sup>+</sup> B cells. <h3>Conclusions</h3> Our results suggest that CD38<sup>high</sup>IgD<sup>+</sup> B cells, which are known as activated B cells, highly react to BAFF in pSS patients as compared to HC. Our findings may shed light on the mechanism of B cell activation triggered by BAFF during the pathogenesis of pSS. <h3>Disclosure of Interest</h3> None declared