Immune response toSalmonella typhi Vi-antigen and tolerance to it in T cell deprived mice

The role of T suppressors in the regulation of the immune response toSalmonella typhi Vi-antigen was studied by comparing the immune response to this antigen in T cell deprived mice (B mice) with the immune response in intact animals. Deprivation of T cells was produced by thymectomy or by lethal irradiation and subsequent injection of embryonic liver cells into the mice. The level of the immune response to Vi-antigen was almost identical in the B mice and control animals. The absence of enhancement of the immune response in the B mice shows that not only induction but also regulation of the immune response to the optimal dose of Vi-antigen is thymus-independent in character. Tolerance to Vi-antigen could be induced in B mice by means of cyclophosphamide; the degree of specific inhibition of the immune response, moreover, was the same as in animals possessing T cells. This suggests that the cause of drug-induced tolerance to this antigen is not activation of T suppressors, but rather a true deficiency of immunocompetent clones of B cells.