LYMPHOPROLIFERATIVE ACTIVITY IN NZB MICE tritiated thymidine (3H thymidine), a method which permits a more quantitative estimation of the activity in these tissues than histology alone (Craddock et al., 1964). Furthermore we have also used NZB mice raised under germ-free conditions for this purpose since the appearance of the lymphatic tissues in such mice primarily reflects responses to endogenous and not external stimuli. The results show that, even in germ-free NZB mice, lymphop roliferative activity is an early feature of the disease, preceding the features characteristic of autoimmunity.
MATERIAL AND METHODS
Mice
The conventional NZB mice were originally obtained from the Laboratory Animals Centre, Carshalton, Surrey, England, and have been maintained at Taplow since 1964 by strict inbreeding.
The germ-free NZB mice were supplied by Carworth Incorporated, Rockland, USA. Their derivation, maintenance and histopathological features have been described by East et al. (1967) and by East and Branca (1969).
Germ-free Carworth Farm White (CFW) mice and conventional C57B1 mice of the Taplow colony wire used as control strains.
Approximately two-thirds of the mice in each group were male. The results in male and female mice were not significantly different.