The effect of a protein-free diet on the immune response of rats to sheep red blood cells. Role of the thymus

Abstract

Following immunization with sheep red blood cells (either by a single i.p. injection without adjuvant (A) or by two injections at one week's interval, the first of them combined with complete Freund's adjuvant (B)) rats kept on a protein-free diet showed lower levels of serum hemagglutinins and hemolysins than control rats. The effect of protracted protein depletion on the number of spleen cells forming hemolytic plaques (PFC) or rosettes (RFC) depended on the immunization schedule: with schedule A, the number of PFC per 10 6 lymphocytes decreased markedly, whereas an increase in the number of RFC was observed in most cases. With schedule B, the proportion of PFC remained unchanged while that of the RFC increased to a much greater extent than with schedule A, due to the concomitant drop in the number of other cell types in the spleen. A comparison of the findings obtained in intact rats and in thymectomized rats indicated that involution of the thymus caused by protein deprivation was a major factor contributing to decreased serum antibody levels, in the absence of adjuvant. However, this involution contributed little to quantitative changes of the PFC and RFC brought about by the deficient diet. Apparently, therefore, the number of residual T-lymphocytes in protein-deprived rats is still sufficient to cooperate in the production of PFC and ion particular of RFC.