Suppression of IgE-antibody production by non-polypeptide dialysable thymic factor.

The effect of dialysable thymic extract on the IgE-antibody production in rats was studied. A marked suppression of IgE-antibody production determined by mast cell degranulation and passive cutaneous anaphylaxis tests was found in the immunized rats injected with dialysable thymic extract. The treatment of this preparation with immobilized pronase affects neither its suppressive activity, nor does such treatment affect the activity of purified factor, isolated from the crude extract. The prolonged administration of purified preparation to rats leads to an increase in thymus weight. When syngeneic thymocytes incubated with purified non-polypeptide thymic factor were administered to immunized rats a significant suppression of IgE-antibody production was observed compared to that occurring in untreated ones. On this basis, it was concluded that a decrease of IgE-antibody production may be due to a direct stimulation of T-suppressor cells.