Studies on the role of the thymus and T cells in the in vivo suppression of delayed hypersensitivity (desensitization): radiosensitivity of the mechanism inducing nonspecific anergy.

Guinea pigs immunized with two or more antigens can have their ability to manifest delayed hypersensitivity (DH) reactions to all these antigens temporarily blocked by the administration of large (mg) amounts of one or more of these antigens 9 days after immunization. This nonspecific anergy is called desensitization. This study presents evidence for the induction of the desensitized state by an active, radiosensitive, immunoregulatory mechanism involving the peripheralization of thymocytes. Desensitization was associated with 1) a marked reduction in thymic weight; 2) an increase in mature T cells in the peripheral blood; 3) decreased responsiveness of the lymphocytes in the spleen to concanavalin-A; and 4) markedly reduced numbers of mono-nuclear cells, basophils, and polymorphs at the skin sites of specific and nonspecific desensitization. Small doses of whole-body irradiation which left DH capacity intact prevented nonspecific desensitization, but did not prevent specific desensitization, suggesting that a radiosensitive cell was involved in the production of anergy.