Jonathan J Kotzin1,2, Walter K Mowel1,2, Jorge Henao-Mejia3,2,4. 1. Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. 2. Institute for Immunology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. 3. Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. jhena@pennmedicine.upenn.edu. 4. Divisions of Protective Immunity and Transplant Immunology, Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, PA 19104, USA.