AB0174 Increased Proportion of CD38+Igd+ B Cells Contributes to Pathogenesis of Primary SjÖGren's Syndrome
Authors: E. Ishioka, K. Yoshimoto, A. Nishikawa, K. Suzuki, T. Takeuchi
Journal: Annals of the Rheumatic Diseases (2014)

<h3>Background</h3> Primary Sjögren9s syndrome (pSS) is characterized by overproduction of autoantibodies against nuclei etc. and clinical manifestations caused by immune complexes, such as peripheral neuropathy, vasculitic lesions and hypocomplementemia. These denote B cell hyperactivity, which is considered to play a key role in pathogenesis of pSS. However, detailed molecular mechanisms of hyperactivation of B cells still remain to be clarified. <h3>Objectives</h3> In the present study, we investigated the mechanism of the abnormal activation of B cells in pSS patients. To this end, we employed FACS to analyze surface markers of B cells such as CD38 and IgD, both of which characterize activated B cell subsets. <h3>Methods</h3> Peripheral B cells were prepared from pSS patients (n=10) and age matched normal individuals (n=6) with anti-CD19-coated microbeads. CD19, CD38 and IgD-triple positive cells were prepared by a cell sorter from peripheral blood samples of normal individuals (n=3). Surface markers of B cells were analyzed with direct immunofluorescence by FACS. B cells were stimulated in vitro with a combination of an anti-IgM antibody, recombinant CD40 ligand (rhCD40L), recombinant human IL-4 (rhIL-4) and recombinant human soluble BAFF (rhsBAFF). The amounts of IgG in the culture supernatants were measured by ELISA. <h3>Results</h3> FACS analysis of whole blood samples revealed that the proportion of CD38<sup>+</sup>IgD<sup>+</sup> B cells among whole B cells, which represent an activated and differentiated B cell subset, was significantly higher in pSS patients than that in normal individuals (p=0.012). In addition, IgG production by pSS B cells was significantly increased as compared to normal B cells when the cells were stimulated in vitro with a combination of an anti-IgM antibody, rCD40L, rhIL-4 and rhsBAFF. Notably, the proportion of CD38<sup>+</sup>IgD<sup>+</sup> was significantly and positively correlated with the serum IgG level among pSS patients (R<sup>2</sup>=0.5723). These results raise the possibility that increased serum IgG level in pSS patients was attributed to an increase in the population of this activated B cell subset. To address this issue, CD38<sup>+</sup>IgD<sup>+</sup> B cells were prepared from normal individuals and IgG production in vitro was examined. Co-stimulation of this subset induced production of considerable amount of IgG, while the induction was only marginal with CD38<sup>+</sup>IgD<sup>–</sup>, CD38<sup>–</sup>IgD<sup>+</sup> or CD38<sup>–</sup>IgD<sup>–</sup> subsets. These data collectively suggest that increase in a population of a CD38<sup>+</sup>IgD<sup>+</sup> subset of B cells is responsible for increased serum IgG level in pSS patients. <h3>Conclusions</h3> Our results suggest that abnormal increase in a population of CD38<sup>+</sup>IgD<sup>+</sup> B cells is involved in IgG over production and hence in the pathogenesis of pSS. <h3>Disclosure of Interest</h3> None declared <h3>DOI</h3> 10.1136/annrheumdis-2014-eular.4060