Host Innate Immune Responses to Fungal Pathogens. The overall goal is to define innate immune responses, including the regulation of IL-1β in mucosal candidiasis. We have developed a murine model of oropharyngeal candidiasis (OPC) to define the innate immune pathways involved in susceptibility to oral colonization, dissemination of infection, and persistence of infection. In this project, critical innate receptors involved in the pathogenesis of localized and disseminated infection in OPC will be identified. We have found a critical role for the β-glucan receptor dectin-1 and TLR2, but not TLR4 in protecting the host from dissemination of infection from the oral site. Similarly, the common adaptor MyD88 was found to be critical in host defense against dissemination as well as limiting mucosal colonization. As MyD88 is also an adaptor for the IL-1 receptor, we also challenged IL-1R knockout mice with C. albicans and found there was heavier colonization of the oral cavity and increased systemic dissemination of infection in the Il1r1-/- mice, demonstrating the importance of IL-1 in protecting the host from dissemination of infection in OPC.
The synthesis, processing and release of IL-1β are tightly regulated and require at least two distinct stimuli. Aninflammatory stimulus causes accumulation of large intracellular stores of the 31-kDa pro-IL-1β (step 1), while a second stimulus activates a multiprotein complex, commonly referred to as the “inflammasome”, which controls the activation of caspase-1 and cleavage of the pro-IL-1β (step 2) followed by release of the active mature 17-kDa IL-1β (step 3). The activation of caspase-1 (step 2) is controlled by the inflammasome, which consists of one or more NALP proteins (see Fig 1). We have showed a critical role for the NALP3/ASC inflammasome complex in the activation of caspase-1 and the processing of proIL-1β (signal 2) in response to Candida albicans. Future plans include defining the mechanism of Candida activation of the NLRP3 inflammasome, defining the impact of the IL-17 axis in the OPC model, and developing multiplexed SNP assays for NLR and IL-1 family genes for use in human studies.
Figure 1: Overview of Specific Aims in the IL-1β regulatory and processing pathways.
Innate Responses to Rift Valley fever virus. We are also investigating innate immune receptors and pathways in viral infections, including Rift Valley fever virus (RVFV). This Phlebovirus is designated a Category A biodefense pathogen based upon its projected severe impact on public health and agriculture in North America in the event of a deliberate release. RVFV (family: Bunyaviridae, genus: Phlebovirus) has a single-stranded, tripartite ambisense coded RNA encoding four structural proteins: viral RNA-dependent RNA-polymerase (L segment), glycoproteins Gn and Gc (M segment) and nucleocapsid protein NP (S segment). Episodic epidemics of RVF present a significant natural threat to human health in many countries of Africa and the Middle East, causing retinitis, encephalitis and hemorrhagic fever. RVFV outbreaks also seriously affect livestock, including sheep, cattle, goats, buffalo, and camels, creating serious economic disruption and risk of famine. Currently there is no specific treatment for RVF and little is known about why RVFV infection leads to a variable progression of human disease. Currently, field studies are being carried out in Eastern Kenya with collaborators Dr. Charles King (CWRU), Dr. Desiree LaBeaud (Oakland Children’s Hospital and CWRU), Dr. James Kazura (CWRU) and Dr. CJ Peters (UTMB, Galveston, TX) where an outbreak of RVFV occurred in 2006. Another project in collaboration with K Fitzgerald at UMass aims to define critical innate receptors, including TLRs, RIGi and Mda-5 and signaling pathways in host protective type-I IFN responses to RVFV. A second project, in collaboration with Dr. Mark Buller (SLU) has established in vitro models of human mucosa as well as an in vivo mouse model of inhalational challenge to define epithelial susceptibility and innate responses to RVFV. Future directions will build on these models to define innate-adaptive cross talk and initiate and optimize mucosal vaccination approaches to RVFV.