Mechanism of tolerance toSalmonella typhi Vi antigen induced with cyclophosphamide

Treatment with Vi antigen followed after 46–48 h by cyclophosphamide induces a state of specific areactivity in mice which persists through adoptive transfer. Only trace amounts of Vi antigen were found in the blood and spleen of the tolerant mice after 2–3 weeks. No T suppressors were found in the spleen of the tolerant animals: Cells of the tolerant mice did not depress the immune response of normal lymphocytes when cultured togetherin vivo and they did not induce tolerance in intact recipients; the cells of normal donors partially restored the immunoreactivity of the tolerant animals. The results suggest that this form of tolerance is due to elimination or prolonged inactivation of the immunocompletent cells.