Adaptive immune responses in bats

Project Summary Bats are reservoir hosts of many zoonotic viruses that cause significant disease in humans, including coronaviruses, filoviruses and henipaviruses. It is unknown how bats can host these viruses but some have speculated that tolerance may be a primary factor. What is clear is that infection of bat reservoirs is typically innocuous, without meaningful inflammatory responses, and often with low antibody titers, suggesting poor affinity maturation. T cells are critical arms of the adaptive immune response and it may be that in bats they play a more prominent role during infection than do B cell responses. This project will determine the effector functions of helper (Th) and cytotoxic (CTLs) T cells to H18N11 bat influenza A virus and BANAL-52 coronavirus, determine how vaccination and T cell depletion impact infection, and whether antibody alone is sufficient to control infections. Helper T cell subsets are essential for the orchestration of immune responses to control infections and have critical impacts on B cells, including directing them to undergo somatic hypermutation leading to affinity maturation of antibodies, class switching and clonal expansion, and some account for immunological tolerance. In contrast, CTLs are instrumental in identifying and killing virally-infected cells. This project will use Jamaican fruit bats (Artibeus jamaicensis) from a closed, captive breeding colony to stimulate antigen-specific T cell responses. We will determine if bats possess canonical helper T cell subsets, including Th1, Th2, Tfh, Treg and Th17 cells, and CTLs, and how these subsets participate in the control and clearance of virus with or without vaccination. We will identify subsets using single-cell RNA Seq and qPCR and determine their cytokine and transcription factor profiles in response to antigenic stimulation. We will also deplete T cells from bats to determine the importance of Th cells and CTLs during infection, and determine whether antibody alone is sufficient to protect bats by using adoptive transfer of hyperimmune bat sera to bats depleted of T cells and challenged with virus. Finally, we will establish the methodology for in vitro cultivation of antigen-specific bat T cell clones that can be used for functional studies of effector molecules. Together, this project will be the first to examine antigen-specific T cells from bats in detail, determine their characteristics in response to vaccination and viral challenge, and the role of arms of the adaptive immune response in bats. Collectively, these studies will offer explanations as to how bats control viral infections without disease, and whether T cells are involved in immune tolerance.