1. Central Institute for the Breeding of Laboratory Animals TNO, PO Box 167, 3700 AD Zeist, The Netherlands; National Institute for Public Health and Environmental Hygiene, PO Box 1, 3720 BA Bilthoven, The Netherlands
2. Central Institute for the Breeding of Laboratory Animals TNO, PO Box 167, 3700 AD Zeist, The Netherlands
3. Medical Research Council Laboratory Animals Centre, Medical Research Council Laboratories, Woodmansterne Road, Carshalton, Surrey SM5 4EF, United Kingdom
4. National Institute for Public Health and Environmental Hygiene, PO Box 1, 3720 BA Bilthoven, The Netherlands