Ectopic lymphoid structures support Epstein-Barr virus persistence and autoreactive plasma cell infection in Rheumatoid Arthritis synovium and Sjogren’s Syndrome salivary glands

Abstract

The ubiquitous ɣ-herpesvirus Epstein-Barr virus (EBV) infects B cells and modifies their differentiation programme leading to B cell activation and immortalization. Although different evidences support a link between EBV infection and rheumatoid arthritis (RA) and Sjogren’s syndrome (SS), the exact role of EBV in RA and SS pathogenesis remain elusive. Recently ectopic lymphoid structures (ELS) have been identified as preferential niches for EBV persistence and reactivation in patients with multiple sclerosis and myasthenia gravis. Independent studies demonstrated that around 50% of RA synovia and 30% of SS salivary glands are characterised by the development of functional ELS, capable to promote local differentiation of autoreactive plasma cells. In this PhD project I explored the potential role of EBV in RA and SS pathogenesis by analysing EBV infection in the RA synovium and SS salivary glands and its relationship with ELS, in situ autoreactive plasma cell differentiation, pathogenic autoantibodies production and cytotoxic immune response. In this work I demonstrated that: i) markers of EBV latent and lytic infection are consistently associated with the presence of ELS in the RA synovium and SS salivary glands; ii) latent EBV proteins are preferentially expressed by B cells, while viral reactivation occurs in plasma cells; iii) a large subset of autoreactive plasma cells is EBV lytically infected in the RA synovia and SS salivary glands; iv) antibodies specific for unmodified and citrullinated EBV peptides, known to cross-recognize ACPA, are produced within ectopic lymphoid structures as 8 demonstrated in vivo in human RA/SCID chimeras; v) SS salivary gland grafts transplanted into SCID mice release human IgG against EBV antigens, whose production correlates with the level of SS-associated auto-antibodies and vi) analysis of CD8+ and CD4+ T-cell localization and granzyme B expression indicated that EBV persistence in ELS-containing RA synovia and SS salivary glands may be favoured by exclusion of CD8+ T cells from B-cell follicles and impaired CD8-mediated cytotoxicity. Overall, these results redefine a novel and pathogenically relevant role for EBV in B-cell dysregulation and chronic inflammation in RA synovium and SS salivary glands.