Downloaded from www.microbiologyresearch.org by Coxsackievirus counters the host innate immune response by blocking type III interferon expression Katharina Lind, Emma Svedin, Erna Domsgen, Sebastian Kapell, Olli H. Laitinen,† Markus Moll and Malin Flodström-Tullberg Correspondence Malin Flodström-Tullberg malin.flodstrom-tullberg@ki.se Received 18 November 2015 Accepted 1 March 2016 Center for Infectious Medicine, Department of Medicine Huddinge, Karolinska Institutet, Stockholm, Sweden Type I IFNs play an important role in the immune response to enterovirus infections. Their importance is underscored by observations showing that many enteroviruses including coxsackie B viruses (CVBs) have developed strategies to block type I IFN production. Recent studies have highlighted a role for the type III IFNs (also called IFNls) in reducing permissiveness to infections with enteric viruses including coxsackievirus. However, whether or not CVBs have measures to evade the effects of type III IFNs remains unknown. By combining virus infection studies and different modes of administrating the dsRNA mimic poly I : C, we discovered that CVBs target both Toll-like receptor 3- and MDA5/RIG-I-mediated type III IFN expression. Consistent with this, the cellular protein expression levels of the signal transduction proteins TRIF and IPS1 were reduced and no hyperphosphorylation of interferon regulatory factor 3 was observed following infection with the virus. Notably, decreased expression of full-length TRIF and IPS1 and the appearance of cleavage products was observed upon both CVB3 infection and in cellular protein extracts incubated with recombinant 2A pro , indicating an important role for the viral protease in subverting the cellular immune system. Collectively, our study reveals that CVBs block the expression of type III IFNs, and that this is achieved by a similar mechanism as the virus uses to block type I IFN production. We also demonstrate that the virus blocks several intracellular viral recognition pathways of importance for both type I and III IFN production. The simultaneous targeting of numerous arms of the host immune response may be required for successful viral replication and dissemination. INTRODUCTION Coxsackieviruses are small positive-strand RNA viruses that belong to the genus Enterovirus in the family Picornaviridae. The coxsackievirus genome is approximately 7.5 kb and it encodes a single polyprotein. The polyprotein is cleaved by two virus-encoded proteases, 2A (2A pro ) and 3C (3C pro ), into structural and non-structural proteins (Pal- lansch & Roos, 2007). Coxsackieviruses infect their hosts via the gastrointestinal tract. They have a broad tissue tropism and can cause severe diseases such as aseptic meningitis, myocarditis, hepatitis and pancreatitis (Huber, 2008; Pal- lansch & Roos, 2007). Moreover, several observations have linked coxsackievirus infections to the development of chronic dilated cardiomyopathy (Chapman & Kim, 2008) and type 1 diabetes (Knip & Simell, 2012; Yeung et al., 2011). Our understanding of the mechanisms behind virus- induced pathologies is limited, in part due to the lack of a complete understanding of how the virus interacts with the host. The induction of type I IFN is an early immune response to a viral infection. In humans, type I IFNs comprise several IFNa subtypes and single isoforms of IFNb,-",-k and -! (de Weerd & Nguyen, 2012; Stetson & Medzhitov, 2006). A more recently described group of IFNs is the type III IFNs, also called the IFNls. To date, this family has four members IFNl1 (IL29), IFNl2 (IL28a), IFNl3 (IL28b) and IFNl4 (Egli et al., 2014; Hermant & Michiels, 2014; Lazear et al., 2015). Type III IFNs bind to a specific receptor, the IFNl- receptor (IFNlR) consisting of two subunits, IFNLR1 and IL10R2. While the type I IFN receptor (IFNAR) is expressed on all nucleated cells, the IFNlR is only expressed on some immune cells and cells of an epithelial origin such as hepa- tocytes and pancreatic islet cells (de Weerd & Nguyen, 2012; Li et al., 2009; Lind et al., 2013). Similar to type I IFNs, the type III IFNs interfere with the replication of several viruses including hepatitis B, hepatitis C, rhinovirus and human immunodeficiency virus (Egli et al., 2014; Hermant & Michiels, 2014; Lazear et al., 2015). †Present address: Institute of Biosciences and Medical Technology, University of Tampere, Tampere, Finland. Eight supplementary figures are available with the online Supplementary Material. 1368 000443 ã 2016 The Authors Printed in Great Britain Journal of General Virology (2016), 97, 1368–1380 DOI 10.1099/jgv.0.000443