The role of B cells in the development of Sjögren's syndrome

Abstract

Sjögren’s syndrome (SS) is a common systemic autoimmune disease characterized by the focal lymphocytic infiltration in exocrine glands and elevated serum anti-SSA autoantibodies. To date, there is no specific treatment for SS. Although autoreactive B cells are known to be involved in the pathogenesis of SS, both phenotypic and functional features of autoreactive B cells in SS remain largely unknown. This study aimed to identify pathogenic B cell subset during the development of experimental SS (ESS) in mice and explore the therapeutic strategy for treating ESS. In ESS mice, CCR6+CD11c+ double positive (DP) B cells were found significantly expanded in the spleens and salivary glands (SGs). Flow cytometric analysis and immunofluorescence microscopy revealed that DP B cells expressed high levels of transcription factor T-bet. Likewise, CD11c+ B cells also increased in the spleen of NOD mice. In the presence of anti-CD40, IL-21 and CpG stimulation, sorting-purified DP B cells exhibited augmented anti-SSA and anti-M3R IgG secretion. Moreover, adoptive transfer of DP B cells from ESS mice led to reduced saliva flow rates and increased IgG deposition in salivary glands in Rag-2-/- recipients. In addition, the phenotypic characteristics of CD11c+ B cells in pSS patients were also investigated. Similarly, circulating DP B cells were significantly increased in pSS patients compared with healthy controls. These B cells were also enriched in the labial glands of patients with pSS, highlighting their involvement in the SS pathogenesis. Furthermore, the transcriptional analysis revealed that DP B cells share similar phenotypes of memory B cells with the high mRNA expressions of ZBTB32 and FCRL5. Mechanistic studies were performed to examine the molecular signals involved in regulating DP B cell differentiation. In culture, IL-21 was found to promote the formation of DP B cells, suggesting a role of IL-21-mediated signaling pathway in DP B cell differentiation. Moreover, blockade of IL-21 signaling pathway via SG cannulation of neutralizing antibodies significantly ameliorated the disease progression in ESS mice and reduced the autoantibody production of DP B cells in pSS patients. Pirfenidone (PFD) is an anti-fibrotic agent approved for treating patients with idiopathic pulmonary fibrosis, but whether PFD has any therapeutic effects in SS remains unclear. In ESS mice, the efficacy of pirfenidone treatment was evaluated. After the pirfenidone treatment, ESS mice displayed significantly improved saliva secretion and decreased lymphocytic infiltration in SG tissue. Importantly, DP B cells and Tfh cells were reduced in pirfenidone-treated ESS mice compared with vehicle controls, suggesting that pirfenidone may exert its therapeutic effects in SS via suppressing DP B and T cell responses. Together, these findings have revealed that DP B cells play a pathogenic role in the development of SS. Moreover, activated IL-21 signaling pathway plays a critical role in the differentiation of DP B cells. The findings on the effects of pirfenidone in targeting DP B cells and ameliorating ESS disease progression have provided a new potential therapy for the treatment of SS. (481 words)