Restoration of delayed hypersensitivity to sheep erythrocytes by thymosin treatment of T-cell-depleted mice.

Calf thymosin was injected subcutaneously in daily doses of 0.1 to 3 mg for 12 to 15 days into adult thymectomized, irradiated, bone marrow-reconstituted (THXB) mice. Thymosin partially restored the ability of the T-cell-depleted host to develop delayed-type hypersensitivity to sheep erythrocytes. The degree of restoration varied from 50 to 75% of control values. Thymosin treatment of normal mice potentiated the footpad responsiveness to sheep erythrocytes by as much as 50% over that of untreated controls. The optimum dosage of thymosin seemed to be in the 200- to 500-mug range, and multiple injections were essential for a significant response. Tweleve daily injections of 100 to 500 mug of thymosin restored T-cell reactivity to the THXB mouse, but the responsiveness decayed relatively rapidly once the treatment was stopped. The restoration of immune responsiveness to sheep erythrocytes in T-cell-depleted mice provides a convenient means of demonstrating activity in thymosin preparations in vivo.