STAT3 Variants as a Rheostat of Immune Tolerance Mouse Core Project Summary The use of genetically altered mice has revolutionized the study of complex biological processes, including immune tolerance and autoimmunity. All the projects in this P01 rely heavily on the use of genetically modified transgenic, knockout, and autoimmune-prone mouse strains. Many autoimmune prone and immunodeficient lines require specific expertise and conditions for optimal research, including housing in pathogen-free environments. Additionally, breeding and care of such animals can become complex when dealing with multiple genetically modified lines and different genetic strains of mice. A mouse Core is envisioned that will help streamline and improve efficiencies with the generation and maintenance of genetically complex lines in a healthy, pathogen-free environment. Because of the reliance of several P01 projects on the NOD mouse model of diabetes and the novel STAT3 gain of function (GOF) mouse lines, much of the Core efforts will revolve around the maintenance, distribution and use of these lines in combination with other relevant immune system reporters or immunodeficient lines. In this way, the Core can help ensure the quality, genetic lineage, and sharing of animals needed for the collaborative studies of the P01 investigators.