The thymic factor system.

Thymus is widely thought as playing the central role in the control of T-cell differentiation. A review of the literature suggests a more general role is displayed by the thymus, envisioned as a part of a hypothalamo-hypophyseal-thymic axis to control the production of hormones and transmitters which, in turn, regulate immune function. Products of macrophages and lymphocytes interfere with the hypothalamus to modify behavior and immune response, in the presence of a foreign body. Brain neocortex controls thymic and extrathymic factors involved in T-cell differentiation.