Release of an immunologically active humoral factor from the isolated perfused thymus.

Experiments were carried out to test whether a humoral factor capable of restoring immunological competence to neonatally thymectomized animals was released by the isolated perfused rabbit thymus. New Zealand white rabbits thymectomized within 24 hours of birth received twice weekly injections of cell-free thymic perfusate from the second week of life. Their body weights, peripheral blood lymphocyte counts, and delayed hypersensitivity responses to skin test antigens were compared with those of two control groups of thymectomized rabbits, one that received injections of cell-free perfusate that had been run in a perfusion circuit with no thymus, and another that received no injections, and also with those of normal or sham-thymectomized rabbits. The results suggest that a humoral factor was liberated from the thymus during perfusion which restored delayed hypersensitivity responses to thymectomized rabbits, but had no effect on the depressed lymphocyte count resulting from thymectomy.