Increased expression of Toll-like receptors 7 and 9 in myasthenia gravis thymus characterized by active Epstein–Barr virus infection

• Published in: Immunobiology (1979) Vol. 221; no. 4; pp. 516 - 527
• Main Authors: Cavalcante, Paola, Galbardi, Barbara, Franzi, Sara, Marcuzzo, Stefania, Barzago, Claudia, Bonanno, Silvia, Camera, Giorgia, Maggi, Lorenzo, Kapetis, Dimos, Andreetta, Francesca, Biasiucci, Amelia, Motta, Teresio, Giardina, Carmelo, Antozzi, Carlo, Baggi, Fulvio, Mantegazza, Renato, Bernasconi, Pia
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier GmbH 01.04.2016
• Subjects: Adolescent; Adult; Advanced Basic Science; Allergy and Immunology; Antigens, Viral - genetics; Antigens, Viral - immunology; B-Lymphocytes - immunology; B-Lymphocytes - pathology; B-Lymphocytes - virology; Cell Proliferation; Dendritic Cells - immunology; Dendritic Cells - pathology; Dendritic Cells - virology; Epstein-Barr virus; Epstein-Barr Virus Infections - complications; Epstein-Barr Virus Infections - immunology; Epstein-Barr Virus Infections - pathology; Epstein-Barr Virus Infections - virology; Female; Gene Expression Regulation; Germinal Center - immunology; Germinal Center - pathology; Germinal Center - virology; Herpesvirus 4, Human; Humans; Interferon-beta - genetics; Interferon-beta - immunology; Ki-67 Antigen - genetics; Ki-67 Antigen - immunology; Lymphocyte Activation; Macrophages - immunology; Macrophages - pathology; Macrophages - virology; Male; Myasthenia gravis; Myasthenia Gravis - complications; Myasthenia Gravis - immunology; Myasthenia Gravis - pathology; Myasthenia Gravis - virology; RNA, Messenger - genetics; RNA, Messenger - immunology; Signal Transduction; Thymus; Thymus Gland - immunology; Thymus Gland - pathology; Thymus Gland - virology; Toll-like receptor 7; Toll-Like Receptor 7 - genetics; Toll-Like Receptor 7 - immunology; Toll-like receptor 9; Toll-Like Receptor 9 - genetics; Toll-Like Receptor 9 - immunology; LMP1; DAPI; RIG-I; EBER; Toll-like receptor 7; Toll-like receptor 9; mDC; SLE; pDC; RA; Thymus; IFN; AChR; TEC; Myasthenia gravis; LCM; EBV; IRF8; MG; TLR; GC; Epstein–Barr virus; myasthenia gravis; plasmacytoid dendritic cell; laser-capture microdissection; 4′,6-diamidino-2-phenylindole, dihydrochloride; acetylcholine receptor; systemic lupus erythematosus; retinoic acid inducible gene-I; EBV-encoded small RNA; Toll-like receptor; myeloid dendritic cell; thymic epithelial cells; germinal center; Epstein–Barr virus latent membrane protein 1; interferon; rheumatoid arthritis; interferon regulatory factor 8
• ISSN: 0171-2985; 1878-3279
• DOI: 10.1016/j.imbio.2015.12.007

•TLR7 and TLR9 mRNA levels are increased in EBV-infected MG thymuses.•TLR7 and TLR9 are overexpressed in MG thymic B cells and co-localize with EBV.•MG thymuses show an increased proportion of proliferating B cells.•TLR7 and TLR9 are overexpressed in MG thymic epithelium, pDCs and macrophages.•In EBV-positive MG thymuses, TLR7 mRNA levels correlate with those of INF-β. Considerable data implicate the thymus as the main site of autosensitization to the acetylcholine receptor in myasthenia gravis (MG), a B-cell-mediated autoimmune disease affecting the neuromuscular junction. We recently demonstrated an active Epstein–Barr virus (EBV) infection in the thymus of MG patients, suggesting that EBV might contribute to the onset or maintenance of the autoimmune response within MG thymus, because of its ability to activate and immortalize autoreactive B cells. EBV has been reported to elicit and modulate Toll-like receptor (TLR) 7- and TLR9-mediated innate immune responses, which are known to favor B-cell dysfunction and autoimmunity. Aim of this study was to investigate whether EBV infection is associated with altered expression of TLR7 and TLR9 in MG thymus. By real-time PCR, we found that TLR7 and TLR9 mRNA levels were significantly higher in EBV-positive MG compared to EBV-negative normal thymuses. By confocal microscopy, high expression levels of TLR7 and TLR9 proteins were observed in B cells and plasma cells of MG thymic germinal centers (GCs) and lymphoid infiltrates, where the two receptors co-localized with EBV antigens. An increased frequency of Ki67-positive proliferating B cells was found in MG thymuses, where we also detected proliferating cells expressing TLR7, TLR9 and EBV antigens, thus supporting the idea that EBV-associated TLR7/9 signaling may promote abnormal B-cell activation and proliferation. Along with B cells and plasma cells, thymic epithelium, plasmacytoid dendritic cells and macrophages exhibited enhanced TLR7 and TLR9 expression in MG thymus; TLR7 was also increased in thymic myeloid dendritic cells and its transcriptional levels positively correlated with those of interferon (IFN)-β. We suggested that TLR7/9 signaling may be involved in antiviral type I IFN production and long-term inflammation in EBV-infected MG thymuses. Our overall findings indicate that EBV-driven TLR7- and TLR9-mediated innate immune responses may participate in the intra-thymic pathogenesis of MG.