OP0276 DENDRITIC CELL-DERIVED IL-27 REGULATES THE MAGNITUDE OF INDUCIBLE ECTOPIC GERMINAL CENTRES BUT FAILS TO DOWNMODULATE IL-17 PRODUCTION IN CD4 T CELLS FROM PATIENTS WITH SJÖGREN’S SYNDROME
Authors: Davide Lucchesi, Rachel Coleby, Elena Pontarini, Edoardo Prediletto, David Hill, Alicia Derrac Soria, Felice Rivellese, Costantino Pitzalis, Simon Jones, Gareth Jones, Michele Bombardieri
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Approximately 30% of Sjögren's Syndrome (SS) patients develop Ectopic Lymphoid Structures (ELS) in their salivary glands (SG). ELS play an active role in autoimmunity and contribute to the development of MALT lymphoma. Interleukin 27 (IL-27) exerts key immunomodulatory actions on CD4 T cells with both pro and anti-inflammatory roles but its role in the formation and regulation of ELS in the salivary glands of SS is unknown. <h3>Objectives</h3> We first used a murine model of inducible SG ELS to elucidate the role of IL-27 and its interaction with IL-17 in the regulation of ELS formation and function. We then extended our observations on a cohort of SS patients to identify IL-27 cellular source, target cells and functional properties in modulating peripheral and lesional CD4 T cells function. <h3>Methods</h3> To trigger ELS formation a single dose of reporter-encoding adenovirus was delivered directly to the SG of wild-type (WT) and IL-27RA-deficient (KO) mice. For IL-17 blockade anti-mouse IL-17A antibody was administered systemically. ELS development and peripheral immune responses were tracked by immuno-histopathology, FACS, and qPCR. Minor SG biopsies were collected from SS and non-specific sialadenitis (sicca) patients. Peripheral blood mononuclear cells (PBMC) isolated from patients and age/sex matched healthy donors (HD). For in vitro experiments PBMCs, isolated CD4 T cells and parotid gland MCs were incubated with IL-27 and analysed by FACS for CD4 T cell subsets while cytokines levels were measured intracellularly by FACS and in culture supernatants. Tissue IL-27 was assessed in SS SG sections by multicolour immunofluorescence to identify IL-27 producing cells. <h3>Results</h3> In WT mice, SG ELS formation was preceded by an upregulation of IL-27p28 and infiltration of IL-27 producing cells (CD11b+ first followed by CD4 and CD8 T cells). KO mice displayed larger, more abundant ELS in the SG with more germinal centres and higher levels of ELS-related genes (<i>Cxcl13</i>, <i>Ccl19, Ltb</i>, <i>Aid</i>) compared to WT mice. During ELS formation, KO mice had an uncontrolled SG Th17 response and systemic IL-17A blockade caused reduction in ELS size and in the expression of ELS-related genes. In SS patients SG and serum, we observed higher expression levels of IL-27 transcripts and protein, respectively, compared to sicca, while SG IL-27 was selectively increased in the ELS+ subset of SS. Immunofluorescence staining for IL-27 revealed its presence primarily in the T cell rich areas of SG ELS with frequent co-localization with DC-LAMP+ dendritic cells. Finally, while IL-27 was able to significantly downregulate IL-17 production in HD, CD4 T cells from patients with SS failed to downregulate IL-17 but showed an aberrant IFNγ release upon IL-27 incubation. We did not observe any difference in IL-27R expression or downstream STAT1/3 phosphorylation between SS and HD. <h3>Conclusion</h3> IL-27 is a critical regulator of the magnitude of the germinal centre response in the SG by restricting Th17 expansion. Both in murine inducible ELS and in patients with SS, dendritic cells appear as the main cellular source of IL-27. Although SG IL-27 was increased in the ELS+ subset of SS, it consistently failed to downregulate IL-17 release in CD4 T cells from SS patients suggesting that a profound dysregulation of the IL-27/IL-17 axis play an important role in ELS formation in this condition. <h3>Disclosure of Interests</h3> Davide Lucchesi: None declared, Rachel Coleby: None declared, Elena Pontarini: None declared, Edoardo Prediletto: None declared, David Hill: None declared, Alicia Derrac Soria: None declared, Felice Rivellese: None declared, Costantino Pitzalis Grant/research support from: Celgene, Simon Jones: None declared, Gareth Jones: None declared, Michele Bombardieri Grant/research support from: Celgene, Consultant for: Medimmune&nbsp;