Ontogeny and kinetics of innate immune cells in health and disease

Project Summary Tissue-resident macrophages are found within every tissue in an organism and are at the interface of tissue homeostasis and pathogenesis. In most adult tissues, embryonic-derived and monocytes-derived macrophages coexist and contribute to tissue health. Traditionally, characterizing macrophage ontogeny in different tissues during homeostasis has relied on the pharmaceutic or genetic depletion of tissue-resident macrophages. These approaches, however, are not physiologically relevant. A systematic analysis of distinct macrophage populations within one tissue during homeostasis and post injury is largely lacking due to a dearth of relevant, optically accessible models. The objective of this proposed work is to improve our foundational knowledge of immune cell biology in vivo, focusing on the ontogeny, kinetics, and function of tissue-resident macrophages. We propose an innovative approach which utilizes a novel small and transparent adult vertebrate model, Danionella cerebrum, to address fundamental questions on the biology of macrophages in vivo. This model provides unprecedented optical accessibility to all tissues without the need for surgical manipulation, even in adult and aging animals. We have pioneered the use of D. cerebrum for immune related studies, generated transgenic lines labeling different tissues and cell types, including macrophages/microglia, and established a robust method for longitudinal live imaging of adult D. cerebrum. To facilitate the proposed study, we will develop a genetic fate- mapping system in D. cerebrum that will enable us to track macrophage lineages, analyze their clonality and assess their function. The fate and activity of these lineages will then be followed longitudinally throughout the life of individual animals. This will allow us to compare the behavior of macrophages derived from distinct developmental origins and define their contribution to tissue homeostasis and integrity. Specifically, we will determine the ontogeny, kinetics and phenotypes of macrophages in (1) peripheral tissues, (2) immune privileged tissues post injury and (3) throughout the aging process. Taken together, the in vivo approaches taken by this project will provide an essential understanding of the complex and dynamic cell biology of innate immunity. Insight into the kinetic profiles of innate immune cells during steady state and pathological conditions will permit the development of therapeutic approaches that fine tune the immune response and improve health by boosting the production of beneficial cells in times of need and/or reduce detrimental cells contributing to inflammation and other disease-related conditions.