EFFECTS OF A PROTEIN-FREE DIET OR FOOD RESTRICTION ON THE IMMUNE-SYSTEM OF WISTAR AND BUFFALO RATS AT DIFFERENT AGES

The effects of a protein-free diet or food restriction on the immune s ystem were examined in two rat strains, Wistar and Buffalo, in differe nt age-groups. Unlike Wistar rats, Buffalo rats have an unusually hype rplastic thymus and a large number of peripheral T cells. The protein- free diet (PFD) in rats resulted in marked thymic involution together with a reduction of splenic T cells, both in number and in antibody re sponse to sheep red blood cells. The depressive effect of the PFD on t he immune system was more serious in young immature rats than in older rats, but less serious in Buffalo rats having enhanced T cell functio ns regardless of age. Thymic involution was also accelerated in both s trains of rats by feeding them a restricted amount of the control diet containing well-balanced nutrients (food restriction, FR). In the FR experiment, no significant change was observed in immune functions of Wistar rats. A slight reduction was observed in the immune functions o f Buffalo rats with FR, but absolute levels were distinctly higher in Buffalo rats than in Wistar rats even after FR. These results suggeste d (1) that the thymic function is sensitive to protein deficiency; (2) that a well-balanced dietary condition is necessary for immunological maturation in the early stage of life and preservation of immune func tions at older age; (3) that animals having higher immune functions ar e more resistant to malnutrition than ordinary ones.