Mouse Norovirus Infection Reduces the Surface Expression of Major Histocompatibility Complex Class I Proteins and Inhibits CD8 ⁺ T Cell Recognition and Activation

Abstract

Human Noroviruses are highly infectious, single stranded RNA (ssRNA) viruses and the major cause of non-bacterial gastroenteritis worldwide. With the discovery of Murine Norovirus (MNV) and the introduction of an effective model for norovirus infection and replication, knowledge about infection mechanisms and its impact on the host immune response has progressed. A major player in the immune response against viral infections is the group of major histocompatibility complex (MHC) class I proteins, which present viral antigen to immune cells. We have observed that MNV interferes with the antigen presentation pathway in infected cells by reducing the surface expression of MHC class I proteins. We have shown that MNV infected dendritic cells or macrophages have a reduced surface expression of MHC class I proteins compared to uninfected and bystander cells. Transcriptional analysis revealed that this defect is not due to decreased amount of mRNA, but is reflected at the protein level. A defect we have identified to be mediated via the MNV NS3 protein. Significantly, treatment of MNV-infected cells with the endocytic recycling inhibitor Dynasore completely restored the surface expression of MHC class I, whereas treatment with the proteasome inhibitor MG132 partly restored the surface expression of MHC class I. These observations indicate a role of endocytic recycling and proteasome-mediated degradation of the protein. Importantly, we show that due to the reduced surface expression of MHC class I proteins, antigen presentation is inhibited, resulting in the inability of CD8+ T cells to become activated in the presence of MNV infected cells. Human Noroviruses (HuNoV) are the major cause of non-bacterial gastroenteritis worldwide and cause a great burden on patients and health systems every year. So far, no antiviral treatment or vaccine is available. We show that MNV evades the host immune response by reducing the amount of MHC class I proteins displayed on the cell surface. This reduction leads to a decrease in viral antigen presentation and interferes with the CD8+ T cell response. CD8+ T cells respond to foreign antigen by activating cytotoxic pathways and inducing immune memory to the infection. By evading this immune response MNV is able to replicate efficiently in the host and cells are impaired in their ability to respond to consecutive infections. These findings have a major impact on our understanding of how Noroviruses interact with the host immune response and manipulate immune memory.

Generation of Norovirus-Specific T Cells From Human Donors With Extensive Cross-Reactivity to Variant Sequences: Implications for Immunotherapy

“…We found that NS6 and VP1 immunogenic epitopes were predominantly HLA class II-restricted. The predominance of CD4 + -reactive T cells might be compatible with the notion that murine norovirus reduces the expression of major histocompatibility complex class I proteins and impairs CD8 + T-cell recognition and activation [33]. Gerdemann et al [34] demonstrated similar results in manufacturing human herpesvirus 6-specific T cells, which might also be explained by herpesvirus-derived immune modulation.…”

The Microtubule-Associated Innate Immune Sensor GEF-H1 Does Not Influence Mouse Norovirus Replication in Murine Macrophages

“…Plasmids encoding the 6× HIS-tagged MNV non-structural (NS) proteins (NS1-2–NS7) on a pcDNA3.1 backbone were generated and published previously [17,27]. The GEF-H1 cDNA expression plasmids were kindly donated by Hans–Christian Reinecker [25].…”

Immune Response Modulation by Caliciviruses

“…Many caliciviruses access their hosts through mucosal surfaces that contain a diversity of commensal pathogens; thus, in these sites they interact with hundreds of differential commensal bacteria, which are part of the host immune defense [reviewed in (109–111)]. Particularly, pathogens infecting the intestine, such as HuNoVs and MNVs encounter these microbes with a harmful of beneficial result to the host.…”

“…As previously discussed above, the mechanisms underlying norovirus persistence or clearance are not well-understood; however, studies of MNV persistence strains and its effect on lymphocyte TCD8+ activation suggest that the infection of macrophages and dendritic cells with MNV impairs the antigen presentation pathway by reducing the surface expression of MHC class I proteins early during infection (111). This reduction is the consequence of the MHC class I internalization via the endocytic recycling pathway and proteasome-dependent degradation.…”

“…This phenotype is likely to be caused by the NS3 protein, the NTPase involved in viral genome replication (Figure 2). This reduction of MHC class I levels hinders the presentation of viral peptides, the activation of CD8 + T cells, and the initiation of the cellular immune response (111). This evasion of antigen presentation most certainly has a role in the clearance of the virus from the host, because it is known that the CD8+ T lymphocytes of mice infected with the persistent MNV-CR6 strain have a differential gene expression than those of the acute strain CW3-infected mice; this distinct gene expression alters the TCD8+ cells localization in the mouse organism, as well as its capacity to respond to activation by proliferation.…”