1. Regeneron Pharmaceuticals, Inc., Tarrytown, NY 10591.
2. Institute for Molecular and Cellular Biology, Osaka University, 1-3, Yamada-oka, Suita, Osaka 565, Japan.
3. Department of Medicine IlIl, Osaka University Medical School, 1-1-50, Fukushima, Fukushima-ku, Osaka 553, Japan.