Background: primary Sjogren’s syndrome (pSS) is a chronic autoimmune disease that affects the lacrimal, salivary and other exocrine glands. More and more studies have shown that B cells play a central role in the pathogenesis of SS.

Objectives: We intended to explore the expression of the transmembrane activator, calcium modulator and cyclophilin ligand interactor (TACI) on the B cells, its role in pSS, and possible signal transduction pathways.

Methods: We included 34 naive pSS patients who visited the rheumatology department of Peking University First Hospital, and 37 gender- and age-distribution matched healthy controls (HCs). (1) To compare the B cell subsets, expression of TACI and relevant receptors in pSS patients, peripheral blood mononuclear cells were separated to analyze the ratio of B subsets, TACI, and BAFF-R by flow cytometry; ELISA was applied to detect the serum BAFF and soluble TACI (sTACI) concentration. (2) As for functional research of TACI, CD19+ B cells separated by magnetic sorting were treated under in vitro culture circumstances with raw TACI, TACI knocked down by siRNA, and sTACI analog (telitacicept) intervention with varing doses. The apoptosis, proliferation, differentiation and regulatory capacity on T cells were analyzed by flow cytometry, inflammatory cytokines and immunoglobulin levels in the culture supernatants were detected by CBA. (3) As for TACI-associated signaling pathway exploration, based on our previous miRNA data and relevant report of high quality, miRNA associated with TACI with significantly biased expression was confirmed by RT-qPCR. Screening the target gene of the candidate miRNA, and miRNA overexpression and inhibition experiments were conducted to validate the targeted relationship in B cells. And TACI-associated signaling pathway was explored via overexpressing and inhibiting the target gene.

Results: (1) Compared to HC, peripheral blood B subsets of pSS patients exhibited a significant bias, manifesting as increased proportion of CD19+CD24hiCD38hi Breg and decreased ratio of CD19+CD24+CD38- memory B cells. The expression of TACI in all B subsets was down-regulated, while that of BAFF-R was up-regulated. Both the serum concentration of BAFF and sTACI in pSS patients increased significantly. (2) As for functional research of TACI, in the setting of raw TACI, B cells in the pSS group showed higher apoptosis rate than HC under culture in vitro, where the ligand of TACI (APRIL or BAFF) addition turned the rate comparable; more active proliferation, and impaired capacity of inducing Treg cells to secrete IL-10. When TACI was knocked down by 50%, B cells performed less late apoptosis, significantly increased proliferation, impaired differentiation, significant dysfunction of Breg itself and impaired induction of Treg cells to secrete IL-10. While telitacicept intervention increased early apoptosis rate of B cells, significantly inhibited proliferation in 500ng/mL group and impaired ability of Breg and Treg cells to secrete IL-10. Besides, increased TACI on B cells treated with telitacicept, decreased IgG and increased IgA in the culture supernatants were observed. (3) As for TACI-associated signaling pathway exploration, hsa-miR-30b-5p showed satisfactory correlation between both transmembrane and sTACI. Besides, the expression of hsa-miR-30b-5p was significantly down-regulated, and inhibition its expression in vitro could lead to differentiation retard, impaired secretion of IL-10 by Breg cells. SMAD1 was screened based on database and validated as its target gene by overexpressing and inhibiting hsa-miR-30b-5p in B cell. After targeted up- or down-regulating the transcription of SMAD1 further, the transcription of ID2 downstream the TGF-β/Hippo signaling pathway changed accordingly.

Conclusion: The expression of TACI on peripheral blood B cells was deficient in pSS patients. TACI deficiency was closely associated with the downregulation of hsa-miR-30b-5p, activating TGF-β/Hippo pathway mediated by its target gene SMAD1 and taking part in the pathogenesis of pSS.

Disclosure of Interests: None declared