Immunoregulatory role of Ig isotypes. I. Induction of contrasuppressor T cells for contact sensitivity responses by antibodies of the IgM, IgG1, and IgG3 isotypes.

A profound state of specific tolerance for the contact sensitivity reaction can be produced by i.v. exposure to hapten on the surface of syngeneic macrophages. When the same haptenated cells are incubated with specific antibody to form cell-bound Ag-antibody complexes, i.v. injection induces immunity rather than tolerance. We observe that such cell-bound Ag-antibody complexes induce not only effector cells for contact sensitivity but also hapten-specific contrasuppressor T (Tcs) cells, which are capable of rendering effector cells resistant to the inhibitory effects of Ts cells. Whereas the induction of the effector cells of contact sensitivity by cell-bound complexes required I region compatibility between the injected cells and the recipient, the induction of Tcs cells showed no genetic restriction. On the other hand, induction of contrasuppression required intact Fc on the complexed antibody, inasmuch as F(ab')2 fragments of specific antibody did not induce immunity. In addition, Tcs cells could also be induced by Ag-antibody complexes on opsonized TNP-mouse RBC treated with anti-TNP antibody. Immunity induced by cell-bound Ag-antibody complexes was observed only when antibodies of the IgM, IgG3, or IgG1 isotypes are used to generate the complexes. Further studies demonstrated that the Tcs cells induced in this way displayed the phenotype of Tcs cells described in other systems (Lyt-1+,2- I-J+, Vicia villosa lectin-adherent) and released a hapten-specific contrasuppressor factor. These studies indicate that Tcs cells can be induced independently of other T cells (such as the effector cells of contact sensitivity) and are likely to be responsible for some of the immunoregulatory effects of cell-bound Ag-antibody complexes. The role of antibody isotype in the induction of Tcs cells is discussed.