Project Summary Microbial colonization during development impacts microbiome assembly, immune system functioning, and health outcomes later in life. The central hypothesis of this proposal is that immune equilibrium is established in early development and education of the immune system can be biased by hysteresis from previous host encounters with microbes. The timing and sequence of encounter (i.e., microbial exposure priority effects) may tolerize or promote host immune responsiveness. A novel gnotobiotic (but not axenic/germ- free) model host, the African Clawed Frog, Xenopus laevis, is ideal for probing critical windows and stimulants of immune system development. We invoke Krogh’s principle for this research on education of the immune system in amphibians because “for a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied” (Krogh 1929, The American Journal of Physiology). Early developmental manipulations are easier in a frog than in a mouse, and immune regulatory patterns in amphibians, like mouse and other vertebrates, are analogous to human responses. Amphibians are also ideal for study of fungal infections emerging in humans because of more permissive body temperatures and clear survival readouts. The specific aims are: (1) Immunological Hysteresis Effects on Fusarium Infection and (2) - Immunological Hysteresis Effects on the Microbiome. In Aim 1 we will establish the developmental window for immune education by microbial exposure. We will then compare stimulation by live microbes including individual pathogens, mutualists, or high diversity natural communities, as well as microbe-associated molecular patterns (MAMPs), and host damage signals. We will observe disease outcome with respect to novel or repeat exposure to a clinical dose of Fusarium applied at a climax developmental stage and quantify immune gene transcriptional responses. We will thus test factors by which immunological hysteresis tolerizes the host toward unresponsiveness or primes the host toward responsiveness to the fungal pathogen. This aim will further establish the Xenopus model system for development and immunology as well as emerging fungal pathogens of humans and provide an innovative method for indicating potentially conserved immune gene regulation in amphibians and humans. In Aim 2 we will investigate the impacts of immunological hysteresis on the assemblage of the host microbiome, and measure the potential direct effects of microbial partners on pathogens in culture to determine whether these symbionts are facilitated or inhibited by immunological hysteresis. This aim will engage the training of advanced undergraduate students (trainees) in a Course-based Undergraduate Research Experience (CURE). The aims will be accomplished by leveraging the Xenopus gnotobiotic system, Fusarium infection model, custom NanoString immune gene panel, and inclusion of undergraduate trainees in research using the CURE. The collaborative research team has state-of-the-art facilities and interdisciplinary expertise spanning comparative immunology, the microbiome, and infectious pathogens.

Project Narrative Studies designed to probe the equilibrium model of immunity may be key to making improvements in preventative medicine and health outcomes for wide range of health challenges; in particular, we utilize an emerging fungal disease system. We will develop innovative tools, including the Xenopus gnotobiotic system, Fusarium infection model, custom NanoString immune gene panel, and a training program focused on the inclusion of undergraduate trainees in a Course-based Undergraduate Research Experience. We will advance the study of immunology and provide a clear test of the central hypothesis that immune equilibrium is established in early development and education of the immune system can be biased by hysteresis from previous host encounters with microbes.