1. K.-M. Lee, M. Griffin, R. Khattri, D. K. Hong, J. A. Bluestone, Ben May Institute for Cancer Research, and Committee on Immunology, University of Chicago, Chicago, IL 60637, USA. E. Chuang, Committee on Immunology, and Gwen Knapp Center for Lupus and Immunology Research, University of Chicago, Chicago, IL 60637, USA. W. Zhang and L. E. Samelson, Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA. D....