TLR7 expression increases with disease progression and mediates expansion of distinct B cell subsets in primary Sjogrens Disease

Abstract Primary Sjögren’s Disease (pSD) is a systemic autoimmune disorder in which the exocrine tissue exhibits chronic inflammation. Additionally, patients often experience diminished tear and saliva production along with many extra-glandular disease manifestations. The causes of pSD are poorly understood and no curative treatments are available. Previous studies in our lab conducted in a pSD mouse model demonstrated that TLR7 agonism accelerates pSD pathogenesis and drives expansion of age-associated B cells (ABCs). To extend our prior work, we hypothesized that pSD splenocytes show heightened TLR7 expression and activation, and expansion of B cell subsets linked to autoimmunity relies on TLR7 in pSD mice. We harvested the spleens of pSD females at three different disease time points (pre-disease, clinical disease and advanced stage disease) and performed flow cytometry. Parallel experiments were performed using age and sex-matched healthy controls. Splenocytes were also cultured with the TLR7 agonist Imiquimod (Imq) and IL-6 secretion assessed by ELISA. In addition, spleens were isolated from TLR7-deficient pSD females at the clinical disease stage and flow cytometry was performed. We found splenocytes derived from pSD animals at the clinical disease stage secreted higher levels of IL-6 in response to Imq stimulation as compared to those derived from healthy control animals. TLR7 +B cells and ABCs (B220 +, CD23 −, CD21 −, T-bet +) increased with disease progression in pSD mice. In pSD mice lacking TLR7, ABCs and germinal center B cells were decreased compared to the TLR7-sufficient pSD parental strain. Thus, splenocytes from pSD mice show enhanced sensitivity to TLR7 and TLR7 signaling mediates expansion of ABC subset in pSD. NIH/NIDCR T32 DE023056 NIH/NIDCR R01 DE029472