Suppressor T cells in low zone tolerance. I. Mode of action of suppressor cells.

Low zone tolerance (LZT) to bacteriophage fd seems to be a type of tolerance which is primarily caused by suppressor T cells. The aim of this paper is to analyze their mode of action. For the induction of antigen-specific suppressor cells in hydrocortisone pretreated CBA mice, we use tolerogenic and immunogenic doses of antigen. Suppressor activity can be demonstrated upon transfer of spleen cells into normal syngeneic mice. After immunization these animals are unable to produce IgG antibody against phage fd, whereas the IgM response is not suppressed; The half-life of transferred suppressor cells in nonimmunized animals is 5--6 weeks. The target of suppression are unprimed T helper cells, whereas primed helper cells cannot be blocked. T helper cells become "resistant" to suppression 18--36 h after contact with antigen. Differentiation from unprimed B into B memory cells is unaffected, yet under suppression conditions persisting B memory cells are blocked in IgG production. The experimental data are incorporated into a model of LZT.