Shenghua Zhou

MyD88 is critical for the development of innate and adaptive immunity during acute lymphocytic choriomeningitis virus infection

We investigated the roles of Toll‐like receptor 2 (TLR2) and myeloid differentiation factor 88 (MyD88) in the course of a lymphocytic choriomeningitis virus (LCMV) infection and revealed the following: (i) studies of transfected cells and murine peritoneal macrophages demonstrated that TLR2 and MyD88 are essential for the initial pro‐inflammatory cytokine response (human IL‐8, mouse IL‐6) to LCMV; (ii) TLR2 knockout (KO) mice and MyD88 KO mice challenged with LCMV produced less IL‐6 and monocyte chemotactic protein‐1 in the serum than wild‐type mice; (iii) in contrast to inflammatory cytokines, the production of type 1 IFN (IFN‐α) in response to LCMV was MyD88 independent; (iv) MyD88 plays an essential role in antiviral CD8+ T cell responses, CD8+ T cells in MyD88 KO mice were defective in their expression of intracellular antiviral cytokines; and (v) the failure of MyD88 KO mice to activate CD8+ T cells was accompanied by persistent viral infection in MyD88 KO mice. We demonstrate that TLR‐mediated responses are important in the innate immune response to LCMV and that MyD88 is essential for the control of the LCMV infection and the maturation/activation of virus‐specific CD8+ T cells.

Induction and Inhibition of Type I Interferon Responses by Distinct Components of Lymphocytic Choriomeningitis Virus

ABSTRACT Type I interferons (IFNs) play a critical role in the host defense against viruses. Lymphocytic choriomeningitis virus (LCMV) infection induces robust type I IFN production in its natural host, the mouse. However, the mechanisms underlying the induction of type I IFNs in response to LCMV infection have not yet been clearly defined. In the present study, we demonstrate that IRF7 is required for both the early phase (day 1 postinfection) and the late phase (day 2 postinfection) of the type I IFN response to LCMV, and melanoma differentiation-associated gene 5 (MDA5)/mitochondrial antiviral signaling protein (MAVS) signaling is crucial for the late phase of the type I IFN response to LCMV. We further demonstrate that LCMV genomic RNA itself (without other LCMV components) is able to induce type I IFN responses in various cell types by activation of the RNA helicases retinoic acid-inducible gene I (RIG-I) and MDA5. We also show that expression of the LCMV nucleoprotein (NP) inhibits the type I IFN response induced by LCMV RNA and other RIG-I/MDA5 ligands. These virus-host interactions may play important roles in the pathogeneses of LCMV and other human arenavirus diseases.

Role of Specific Innate Immune Responses in Herpes Simplex Virus Infection of the Central Nervous System

ABSTRACT Herpes simplex virus 1 (HSV-1) causes a spectrum of disease, including herpes labialis, herpes keratitis, and herpes encephalitis, which can be lethal. Viral recognition by pattern recognition receptors plays a central role in cytokine production and in the generation of antiviral immunity. The relative contributions of different Toll-like receptors (TLRs) in the innate immune response during central nervous system infection with HSV-1 have not been fully characterized. In this study, we investigate the roles of TLR2, TLR9, UNC93B1, and the type I interferon (IFN) receptor in a murine model of HSV-1 encephalitis. TLR2 is responsible for detrimental inflammatory cytokine production following intracranial infection with HSV-1, and the absence of TLR2 expression leads to increased survival in mice. We prove that inflammatory cytokine production by microglial cells, astrocytes, neutrophils, and monocytes is mediated predominantly by TLR2. We also demonstrate that type I IFNs are absolutely required for survival following intracranial HSV-1 infection, as mice lacking the type I IFN receptor succumb rapidly following infection and have high levels of HSV in the brain. However, the absence of TLR9 does not impact survival, type I IFN levels, or viral replication in the brain following infection. The absence of UNC93B1 leads to a survival disadvantage but does not impact viral replication or type I IFN levels in the brain in HSV-1-infected mice. These results illustrate the complex but important roles that innate immune receptors play in host responses to HSV-1 during infection of the central nervous system.

Lymphocytic Choriomeningitis Virus (LCMV) infection of CNS glial cells results in TLR2-MyD88/Mal-dependent inflammatory responses

In response to invading pathogens, Toll-like receptors (TLR) play a critical role in the initiation of the innate immune response, which can be either beneficial or detrimental to the host. In the present study, we demonstrated that central nervous system (CNS) glial cells are activated by Lymphocytic Choriomeningitis Virus (LCMV) in a TLR2-MyD88/Mal-dependent manner. Specifically, in response to LCMV, both astrocytes and microglial cells isolated from wild-type (WT) mice produced chemokines, such as MCP-1, RANTES and TNF-alpha. Similar responses occurred in TLR3 KO and TLR4 KO glial cells. In striking contrast, both astrocytes and microglial cells isolated from mice deficient in TLR2, MyD88, and Mal did not produce any of these chemokines. In addition, LCMV infection of glial cells induced up-regulation of TLR2, MHC class-I and II, CD40, CD86 in a MyD88-dependent manner. These results define a functional role for TLR signaling in viral infection-induced activation of CNS glial cells as well as for the immunopathology in the CNS.

MyD88 Intrinsically Regulates CD4 T-Cell Responses

ABSTRACT Myeloid differentiation factor 88 (MyD88) is an essential adaptor protein in the Toll-like receptor-mediated innate signaling pathway, as well as in interleukin-1 receptor (IL-1R) and IL-18R signaling. The importance of MyD88 in the regulation of innate immunity to microbial pathogens has been well demonstrated. However, its role in regulating acquired immunity to viral pathogens and neuropathogenesis is not entirely clear. In the present study, we examine the role of MyD88 in the CD4+ T-cell response following lymphocytic choriomeningitis virus (LCMV) infection. We demonstrate that wild-type (WT) mice developed a CD4+ T-cell-mediated wasting disease after intracranial infection with LCMV. In contrast, MyD88 knockout (KO) mice did not develop wasting disease in response to the same infection. This effect was not the result of MyD88 regulation of IL-1 or IL-18 responses since IL-1R1 KO and IL-18R KO mice were not protected from weight loss. In the absence of MyD88, naïve CD4+ T cells failed to differentiate to LCMV-specific CD4 T cells. We demonstrated that MyD88 KO antigen-presenting cells are capable of activating WT CD4+ T cells. Importantly, when MyD88 KO CD4+ T cells were reconstituted with an MyD88-expressing lentivirus, the rescued CD4+ T cells were able to respond to LCMV infection and support IgG2a antibody production. Overall, these studies reveal a previously unknown role of MyD88-dependent signaling in CD4+ T cells in the regulation of the virus-specific CD4+ T-cell response and in viral infection-induced immunopathology in the central nervous system.

Role of MyD88 in Route-Dependent Susceptibility to Vesicular Stomatitis Virus Infection

TLRs are important components of the innate immune response. The role of the TLR signaling pathway in host defense against a natural viral infection has been largely unexplored. We found that mice lacking MyD88, an essential adaptor protein in TLR signaling pathway, were extremely sensitive to intranasal infection with vesicular stomatitis virus, and this susceptibility was dose dependent. We demonstrated that this increased susceptibility correlates with the impaired production of IFN-α and defective induction and maintenance of neutralizing Ab. These studies outline the important role of the TLR signaling pathway in nasal mucosae-respiratory tracts-neuroepithelium environment in the protection against microbial pathogen infections. We believe that these results explain how the route of infection, probably by virtue of activating different cell populations, can lead to entirely different outcomes of infection based on the underlying genetics of the host.

Discovery of a novel TLR2 signaling inhibitor with anti-viral activity

Blockade of Toll-like receptor (TLR)-mediated inflammatory responses represents a new approach in the development of anti-inflammation therapeutics. In the present study, we have screened for TLR2-mediated inflammation inhibitors from small molecule compound libraries using a sensitive cell line stably expressing TLR2, CD14, and an NF-kappaB-driven-luciferase reporter gene. Lymphocytic choriomeningitis virus (LCMV) was used as a virus model. This arenavirus activates a TLR2/CD14-dependent NF-kappaB signaling pathway. We have identified 10 potential anti-inflammatory compounds out of 101,306 compounds. We further evaluated 1 of these positive compounds, E567. We demonstrated that compound E567 efficiently inhibits both LCMV and Herpes simplex virus 1 (HSV-1) induced cytokine responses in both human and mouse cell cultures. We also demonstrated that E567 inhibits cytokine responses in the mouse. Remarkably, E567 is also capable of inhibiting LCMV replication in mice. This is a new model for developing drugs for use in treating viral illnesses.

Role of Interferon Regulatory Factor 7 in T Cell Responses during Acute Lymphocytic Choriomeningitis Virus Infection

ABSTRACT Type I interferons (IFNs), predominantly IFN-α and -β, play critical roles in both innate and adaptive immune responses against viral infections. Interferon regulatory factor 7 (IRF7), a key innate immune molecule in the type I IFN signaling pathway, is essential for the type I IFN response to many viruses, including lymphocytic choriomeningitis virus (LCMV). Here, we show that although IRF7 knockout (KO) mice failed to control the replication of LCMV in the early stages of infection, they were capable of clearing LCMV infection. Despite the lack of type I IFN production, IRF7 KO mice generated normal CD4+ T cell responses, and the expansion of naïve CD8+ T cells into primary CD8+ T cells specific for LCMV GP33–41 was relatively normal. In contrast, the expansion of the LCMV NP396-specific CD8+ T cells was severely impaired in IRF7 KO mice. We demonstrated that this defective CD8+ T cell response is due neither to an impaired antigen-presenting system nor to any intrinsic role of IRF7 in CD8+ T cells. The lack of a type I IFN response in IRF7 KO mice did not affect the formation of memory CD8+ T cells. Thus, the present study provides new insight into the impact of the innate immune system on viral pathogenesis and demonstrates the critical contribution of innate immunity in controlling virus replication in the early stages of infection, which may shape the quality of CD8+ T cell responses.