Innate immune responses against priority pathogens
Program leader: Jenny Ting
SE-RP-010: Novel roles of the NLR protein in host response against WNV and DENV
University of North Carolina
A major conceptual advance for innate immunity has been the discovery of Pathogen-associated Molecular Pattern recognition receptors or sensors, a prime example being the toll-like receptor (TLR). More recently, we and others discovered a large family of pathogen sensors in humans and mice, called the NLR (nucleotide-binding domain, leucine-rich repeat containing) family, known previously as CATERPILLER, NACHT-LRR, or NOD-like receptor. An important function of NLR proteins is the formation of a biochemically-defined complex, called the inflammasome, which processes pro-caspase-1 and pro-IL-1b/IL-18 to their mature forms. In addition to this role, some NLRs have a profound effect on T cell responses. This creates a new paradigm where NLRs can also influence adaptive immunity. Additional studies indicate that NLR proteins mediate type I interferon (IFN) production in response to viruses through an interference of the intracellular pathway mediated by the mitochondrial anti-viral signaling molecule (MAVS, a.k.a. IPS, VISA and CARDIF). This proposal will examine the divergent roles of NLR during infection by viruses of broad interest to this Center of Biodefense and Emerging Infectious Diseases. As type I IFN is pivotal in anti-viral host defense, and the intracellular pathway of viral RNA recognition is crucial for this response, we will study NLRs that are crucial for host response. Of equal importance, IL-1 production has been observed by several groups as being a crucial outcome of human infection by viruses. Finally, adaptive immunity is unquestionably of importance to anti-viral host response. However, the link between NLR members to any of these anti-viral host responses has not been extensively explored. In this proposal, we plan to explore the roles of different NLRs in eliciting interferon response, inflammasome function, and adaptive immunity upon infection by viruses of interest to SERCEB.
SE-RP-011: Regulation of antibody responses by toll-like receptors
Emory University
Toll-like receptors (TLRs) play a pivotal role in shaping then host immune response to a pathogen or a vaccine. Our understanding of the mechanisms by which this occurs, have arisen from explorations that probe the response of immune cells to a single TLR ligand. However, microbes and vaccines do not simply stimulate a single TLR, but rather stimulate combinations of different TLRs. Recent work by Lanzavecchia and others suggests that the combinatorial activation of multiple TLRs result in a synergistic activation of cytokine production by dendritic cells (DCs). The impact of this synergy on the adaptive immune response is poorly understood. In particular, there is little or no understanding of the innate immune mechanisms that affect critical variables of the B cell response, such as memory B cell generation, affinity maturation, and induction of neutralizing antibodies. Our preliminary data in mice, suggest that TLR ligands administered with an antigen, can elicit antigen-specific antibody responses. In particular, specific combinations of TLR ligands result in a synergistic induction of the antigen-specific antibody responses, and in the induction of high avidity antibodies.
SE-RP-012: TLR7 and responses to flaviviruses
North Carolina State University
Flaviviruses have evolved complex mechanisms to interact with the host immune response. The earliest immune responses to infection involve components of the innate immune system, beginning with the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), such as toll-like receptors (TLRs), and intracellular RNA helicases, such as RIG-I and Mda-5. PAMP recognition results in activation of specific signal transduction pathways that result in production of proinflammatory cytokines, such as type I interferon (IFN), TNFa and others. Type I interferon is one of the most important mediators of the early immune response. Mice deficient in IFN signaling are more susceptible to flaviviruses and pretreatment of mice with type I IFN can prevent flavivirus disease. One of the major pathways of IFN synthesis in viral infection is the stimulation of plasmacytoid dendritic cells (pDCs) via TLRs 7, 8 or 9. While several studies have indicated that flaviviruses are able to stimulate pDCs to produce IFNa, the mechanisms of this stimulation are not understood. Our preliminary data indicated that mosquito-derived flaviviruses stimulate TLR7 only weakly while viruses grown in mammalian cells strongly stimulate TLR7. We have generated preliminary evidence that suggests that the different glycosylation patterns of flavivirus structural proteins obtained in insect and mammalian cells play a role in the differential TLR reponses. In addition, our previous work has shown that WNV, and more specifically its NS1 protein, is able to interfere with TLR3 and TLR7 signal transduction which could prevent further activation of these pathways after initial infection has been established. TLR7 is a PRR that recognizes ssRNA and activates the transcription factors NFkB and interferon-regulatory factor 7 (IRF7), resulting in transcription of IFNa and other cytokines. NS1 is a glycoprotein secreted to high levels during flavivirus infection that can be endocytosed by several cell types. We are investigating a role for secreted NS1 in inhibition of TLR7 function which could influence TLR responses on neighboring uninfected cells and thus contribute to viral pathogenesis. At the same time we are investigating molecular interactions between singling proteins involved in TLR signaling in presence and absence of NS1. To further address a role for TLR7 in WNV pathogenesis we are currently establishing a mouse model of WNV encephalitis using foot pad inoculations with the goal of comparing parameters of WNV pathogenesis and immune responses in wt and TLR7 ko mice.
National Institute of Allergy and Infectious Diseases