P009/O22 Transcriptomics unveils unique biological profile of tertiary lymphoid structures germinal centers

Career situation of first and presenting author Post-doctoral fellow. Introduction The development of the B cell repertoire is regulated by the process of affinity maturation that occurs within the inner part of the B cell follicles within secondary lymphoid organs (SLOs). In autoimmunity process might occur in ectopic lymphoid structures (ELS), aggregates of lymphocytes that form in target organs of disease (i.e. the salivary glands of patients with Sjogren’s Syndrome (SS)). The phenotypical and functional features supporting ELS pathogenic properties have not been identified. Moreover, the functional proof that ELS independently from SLOs contribute to the autoimmune response has not been provided. Objectives To characterise the transcriptome profile of human ELS isolated from SS salivary glands in comparison with SLO and to dissect, in an animal model of ELS development, the ability of ELS to contribute to the autoreactive response. Methods Frozen salivary gland biopsies were obtained from SS patients and selected for presence of germinal center +ELS. Samples were stained and microdissected, RNA isolated and transcribed and used for RNAseq using ClonTech SMARTseq v4 kit. Salivary gland ELS and autoimmunity was established as previoully described1 in FAP-DTR mice. Animals were locally treated (day 2 and 6) with DTX to induce selective ELS disaggregation; glands and serum were harvested for analysis at day 15. Results Transcript analysis provide evidence that the ectopic ELS are characterised by upregulation of TNF, INFg, BAFF, APRIL, CXCL12 and CXCL13, FAS and FASL as compared to SLOs. Sequencing unveiled an alterated cell-proliferation profile with downregulation of BCL6 and AID, the enzymes responsible for B cell affinity maturation. Selective depletion of FAP +cells induced loss of anatomical segregation of ELS and profoundly compromised their anatomy with significant impact on the local autoimmune response. Conclusions Our study provides the first evidence of a significant molecular difference between ELS and SLOs. We demonstrated that, although characterised by similar anatomical organization, ELS pathogenic cytokine signature is associated with low levels of bcl6 and AID and aberrant apoptosis, unveiling impaired regulation of the B cell cycle, responsible for the survival of autoreactive, poorly selected B cell clones. Accordingly, selective depletion of ELS in vivo profoundly impact local and systemic autoimmunity. Reference Barone F, et al. PNAS 2015. Disclosure of Interest None declared.