Project Summary/Abstract (Core B, Barton) Core B of this Program Project Grant (P01) will maintain a colony of mouse strains with deficiencies in components of innate immunity or other genetic modifications useful for the study of innate immunity and the host response to pathogens. Core B also supports the generation of new mouse strains using Cas9-mediated genome editing. This new technology enables rapid and affordable generation of knock-out and knock-in mice. Core B will work with each of the Project Labs to develop new mouse strains that will facilitate hypothesis testing. Mice are cells from the mice maintained within Core B will be distributed to each of the projects within the P01. All mouse strains have been or will be backcrossed onto the C57BL/6J genetic background to equivalent degrees. Core B will reduce overall mouse costs due to economies of scale. In addition, each P01 project will benefit from using cells and mice with fewer genetic and experimental variations.