Another enteric virus, reovirus, also showed decreased infection in pIgR KO mice. pathogenesis. KEYWORDS:RNA virus, enteric viruses, gastrointestinal infection, pathogenesis == ABSTRACT == Noroviruses are enteric pathogens causing significant morbidity, mortality, and economic losses worldwide. Secretory immunoglobulins (sIg) are a first line of mucosal defense against enteric pathogens. They are secreted into the intestinal lumen via the polymeric immunoglobulin receptor (pIgR), where they bind to antigens. However, whether natural sIg protect against norovirus infection remains unknown. To determine if natural sIg alter murine norovirus (MNV) pathogenesis, we infected pIgR knockout Rabbit Polyclonal to SRPK3 (KO) mice, which lack sIg in mucosal secretions. Acute MNV infection was significantly reduced in pIgR KO mice compared to controls, despite increased MNV target cells in the Peyer’s patch. Natural sIg did not alter MNV binding to the follicle-associated epithelium (FAE) or crossing of the FAE into the lymphoid follicle. Instead, naive pIgR KO mice had enhanced levels of the antiviral inflammatory molecules interferon gamma (IFN-) and inducible nitric oxide synthase (iNOS) in the ileum compared to controls. Strikingly, depletion of the intestinal microbiota in pIgR KO and control mice resulted in comparable IFN- and iNOS levels, as well as MNV infectious titers. IFN- treatment of wild-type (WT) mice and neutralization of IFN- in pIgR KO mice modulated MNV titers, implicating the antiviral cytokine in the phenotype. Reduced gastrointestinal infection in pIgR KO mice was also observed with another enteric virus, reovirus. Collectively, our findings suggest that natural sIg are not protective during enteric virus infection, but rather, that sIg promote enteric viral infection through alterations in microbial immune responses. IMPORTANCEEnteric virus, such as norovirus, infections cause significant morbidity and mortality worldwide. However, direct antiviral infection prevention strategies are limited. Blocking host entry and initiation of infection provides an established avenue for intervention. Here, we investigated the role of the polymeric immunoglobulin receptor (pIgR)-secretory immunoglobulin (sIg) cycle during enteric virus infections. The innate immune functions of sIg (agglutination, immune exclusion, neutralization, and expulsion) were not required during control of acute murine norovirus (MNV) infection. Instead, lack of pIgR resulted in increased IFN- levels, which contributed to reduced MNV titers. Another enteric virus, reovirus, also showed decreased infection in pIgR KO mice. Collectively, our data point to a model in which sIg-mediated microbial sensing promotes norovirus and reovirus infection. These data provide the first evidence of the proviral role of natural sIg during enteric virus infections and provide another example of how intestinal bacterial communities indirectly influence MNV pathogenesis. GO6983 == INTRODUCTION == The mucosal surface of the gastrointestinal (GI) tract is a potential entry point for many pathogens. To protect itself from pathogen attack, the host has evolved multiple mechanisms, including the secretion of immunoglobulins, i.e., secretory immunoglobulins (sIg). sIg neutralize microorganisms in the intestinal lumen and reduce the immunogenicity of the remaining bacteria (1). Intestinal epithelial cells transcytose polymeric IgA (pIgA) and pIgM from the lamina propria via the basolaterally expressed polymeric immunoglobulin receptor (pIgR). Once the pIgR-pIgA/M complex reaches the intestinal lumen, the receptor is cleaved, and sIgA GO6983 and sIgM are released (1). Pathogens that have crossed the epithelial barrier and those present in intestinal epithelial cells can also be expelled by this transcytotic process (2). Highlighting the defense function of the process are studies demonstrating that deletion of pIgR results in increased pathogen loads forHelicobacter pylori(3),Giardia muris(4),Salmonellaspp. (5), andClostridium difficile(6). sIgA are the predominant species of immunoglobulins in the intestine (7). In addition to their host defense function, they also play an immunomodulatory role (7). The follicle-associated epithelium (FAE) of Peyers patches (PP) and other mucosa-associated lymphoid follicles contain transcytotic microfold (M) cells. sIgA aid in luminal sampling and the initiation of mucosal immune responses. Selective adherence of luminal sIgA to the M cell surface triggers uptake of sIgA immune complexes into the PP (8), resulting in retrograde sIgA sampling by dendritic cells (DC) (9), noninflammatory activation of DC, and induction of regulatory T cells (7). The sIgA-induced antipathogenic immune responses also nonspecifically reduce the inflammatory potential of macrophages via upregulation of inhibitory receptors (10). Noroviruses (NoV) are the leading cause of acute gastroenteritis worldwide (11,12). Targeting host entry and infection initiation may provide an avenue for intervention, as they are instrumental in determining host range, initiation of immune responses, and pathogenesis. However, limited information is available about factors that promote or inhibit norovirus infection. To gain a better understanding of the early events during norovirus infection in GO6983 a natural host, we took advantage of murine norovirus (MNV), a well-established and highly tractable animal.
