1. *Laboratory of Immune Regulations and Development, Department of Developmental Biology, and
2. †Flow Cytometry Unit, J. Monod Institute, Centre National de la Recherche Scientifique and Universities Paris 6 and 7, Paris, France;
3. ‡Sandoz Pharma, Basel, Switzerland; and
4. §Division of Basic Sciences, National Jewish Center for Immunology and Respiratory Medicine, Denver, CO 80206