1. F.M. is at Division of Allergy, Immunology, and Transplantation, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892.
2. M.G.M. is at Institute for Research in Biomedicine, CH-6500 Bellinzona, Switzerland.
3. A.K.P. is at Baylor Institute for Immunology Research, Dallas, TX 75204.
4. L.D.S. is at The Jackson Laboratory, Bar Harbor, ME 04609.