Hemopoietic inductive environment necessary for an early stage in differentiation of thymic immune cells: Effect of antilymphocytic serum

Abstract

Treatment of adult mice with rabbit anti‐mouse thymocyte serum decreased the number and frequency of alloantigen‐sensitive units responsible for graft‐versus‐host reactions and prolonged the survival of skin allografts. Whereas alloantigen‐sensitive units were suppressed directly in vitro, they were not apparently suppressed directly in vivo since the fall‐off of their numbers and/or function did not occur during the first day after serum injection. Treatment of prospective recipients of thymus cell grafts impaired the production of alloantigen‐sensitive units by transplanted primitive progenitors. Differentiation with proliferation of alloantigen‐sensitive units was less affected. Similarly, treatment of prospective recipients of thymus cell grafts with antilymphocytic serum impaired the production of specific inducer cells responsive to sheep erythrocytes by transplanted more primitive cells, presumably antigenreactive cells. Production of new precursors of anti‐sheep erythrocyte hemolytic plaque‐forming cells by transplanted bone marrow was not affected. Thus, antilymphocytic serum impairs the generation of immunocompetent cells of thymic origin by altering a hemopoietic inductive environment necessary for an early stage in differentiation.