1. Laboratory of Cellular Physiology and ImmunologyThe Rockefeller UniversityNew YorkNew York10021USA
2. Laboratory of Molecular Biology and Immunology, INF 324D‐6900HeidelbergFederal Republic of Germany
3. Max‐Planck‐Institut fur ImmunbiologieD‐7800Freiburg‐ZähringenFederal Republic of Germany
4. School of MedicineSouthern Illionis UniversityCarbondaleIllinois62901USA