FRI0286 Rank-l is expressed by salivary gland epithelial cells in primary sjogren’s syndrome: a novel actor in ectopic lymphoid structure neogenesis

Background Tertiary Lymphoid Organs (TLOs) are observed in target tissues of various immune-mediated inflammatory diseases (IMIDs) such as salivary glands in primary Sjogren’s syndrome1 (pSS). TLOs are mimicking secondary lymphoid organs (SLOs) architecture and strikingly share common features with lymph nodes.2 SLOs organogenesis is coordonated by a complex stromal network that has not been fully characterised in TLOs yet. Although RANK-L (Receptor Activator of NF-kB Ligand) has been recently involved as a pivotal cytokine in precoce steps of lymph nodes development,3 notably through a stromal cell expression, its contribution in TLOs neogenesis remains unclear. Objectives To characterise stromal cells subsets within TLOs arising in the salivary glands and to determine wether RANKL is expressed or not in the the target tissue of pSS. Methods Stromal cells and RANK-L expression were analysed in TLOs from salivary glands by immuno-fluorescence on frozen sections in the NZB/NZW F1 mouse model and in minor salivary gland biopsies of patients fullflling 2016 ACR-EULAR Sjogren’s syndrome criterias and by flow- cytometry after enzymatic digestion of NZB/NZW F1 salivary glands. RANK-L expression has also been assessed by Real Time quantitative Polymerase Chain Reaction (RT-qPCR) and immunofluorescence on primary cultures of salivary gland epithelial cells (SGECs) with or without IL-1b or Interferon alpha (INF-a) stimulation. Results Most of SLOs stromal cells populations: Fibroblastic Reticular Cells (FRCs), Follicular Dendritic Cells (FDCs), Lymphatic Endothelial Cells (LECs), Blood Endotholial Cells (BECs) and High Endothelial Veinules (HEVs) were identified in salivary TLOs of both NZB/NZW F1 mice and patients with pSS. FRCs were the dominant subset in salivary TLOs and their proportion correlated with the degree of lymphocytic infiltration (r=0,7 ; p=0,007). In SLOs, RANK-L was mainly expressed by MRCs, whereas, none of them could be detected in salivary TLOs. However, despite the absence of MRCs in TLOs, RANK-L was still expressed by a few T-cells within the infiltrates and strikingly by epithelial cells. Furthermore, RANK-L expression by SGECs in primary cultures was increased after INF-a or IL-1b stimulation. Conclusions To our knowledge, this is the first report of a RANK-L contribution to primary Sjogren’s syndrome. These results suggest that RANK-L could be an important actor of ectopic lymphoid neogenesis. RANK-L inhibition might represent, in the future, a relevant immuno-modulatory strategy in primary Sjogren’s syndrome. References [1] Corsiero E, Nerviani A, Bombardieri M, Pitzalis C. Ectopic Lymphoid Structures: Powerhouse of Autoimmunity. Front. Immunol. 2016;7:430. [2] Buckley CD, Barone F, Nayar S, Benezech C, Caamano J. Stromal cells in chronic inflammation and tertiary lymphoid organ formation. Annu. Rev. Immunol. 2015;33:715–745. [3] Kong YY, Yoshida H, Sarosi I, Tan HL, Timms E, Capparelli C, et al. OPGL is a key regulator of osteoclastogenesis, lymphocyte development and lymph- node organogenesis. Nature. 1999Jan 28;397(6717):315–23. Disclosure of Interest None declared