1. Committee on Immunology
2. Department of Molecular Genetics, School of Medicine, University of Fukui, Matsuoka, Fukui 910-1193, Japan
3. Laboratory of Lymphoid Tissue Development, Institut Pasteur, 75724 Paris Cedex 15, France
4. Committee on Cancer Biology
5. Committe on Developmental Biology,
6. Department of Pathology, University of Chicago, Chicago, IL 60657