Epstein-Barr virus in tumor-infiltrating B cells of myasthenia gravis thymoma: an innocent bystander or an autoimmunity mediator?
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Paola Cavalcante1, Stefania Marcuzzo1, Sara Franzi1, Barbara Galbardi1, Lorenzo Maggi1, Teresio Motta2, Raffaella Ghislandi2, Antonella Buzzi2, Luisella Spinelli3, Lorenzo Novellino3, Fulvio Baggi1, Carlo Antozzi1, Fabio Conforti4, Tommaso Martino De Pas4, Massimo Barberis5, Pia Bernasconi1 and Renato Mantegazza1
1Neurology IV – Neuroimmunology and Neuromuscular Diseases Unit, Fondazione Istituto Neurologico “Carlo Besta”, 20133 Milan, Italy
2Department of Pathological Anatomy, ASST - Bergamo Est Ospedale Bolognini Seriate, 24068 Seriate Bergamo, Italy
3Department of General Surgery, ASST - Bergamo Est Ospedale Bolognini Seriate, 24068 Seriate Bergamo, Italy
4Unit of Sarcomas and Thymomas, European Institute of Oncology, 20136 Milan, Italy
5Histopathology and Molecular Diagnostics Unit, European Institute of Oncology, 20136 Milan, Italy
Pia Bernasconi, email: [email protected]
Keywords: autoimmunity; myasthenia gravis; Epstein-Barr virus; thymoma; toll-like receptors
Received: July 05, 2017 Accepted: August 04, 2017 Published: September 08, 2017
The thymus plays a key role in myasthenia gravis (MG), a B cell-mediated autoimmune disorder affecting neuromuscular junction. Most MG patients have thymic abnormalities, including hyperplasia and thymoma, a neoplasm of thymic epithelial cells. Epstein-Barr virus (EBV) is associated with autoimmune diseases and tumors. Recently, we showed EBV persistence and reactivation in hyperplastic MG thymuses, suggesting that EBV might contribute to intra-thymic B cell dysregulation in MG patients. Here, we investigated EBV involvement in thymoma-associated MG, by searching for EBV markers in MG (n=26) and non-MG (n=14) thymomas. EBV DNA and EBV-encoded small nuclear RNA (EBER) 1 transcript were detected in 14/26 (53.8%) and 22/26 (84.6%) MG thymomas, and only in 3 of 14 (21.4%) non-MG thymomas. Latent EBNA2 and late gp350/220 lytic transcripts were undetectable in all, but one, thymomas, and early lytic BZLF1 transcript was absent in all samples, suggesting that early infection events and EBV reactivation were very rare in thymomas. EBER1 and 2-positive cells were detected in MG, but not in non-MG, thymomas, as well as cells expressing EBV latency proteins (EBNA1, LMP1, LMP2A), that were mainly of B cell phenotype, indicating EBV association with MG rather than with thymoma. Toll-like receptor (TLR) 3 transcriptional levels were higher in MG than non-MG thymomas and positively correlated with EBER1 levels, suggesting a role for EBERs in TLR3 activation. Our findings show that EBV is commonly present in thymoma-infiltrating B cells of myasthenic patients, indicating a contribution of EBV to B cell-mediated autoreactivity in MG associated with thymic tumor.
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