Restoration of T-cell responsiveness by thymosin: Expression of anti-tuberculous immunity in mouse lungs

Specific pathogen-free, adult thymectomized, irradiated, and bone marrow-reconstituted (THXB) B6D2 mice were infected aerogenically with 1 x 10³ to 5 x 10³ live BCG Pasteur. Seven days later a group of the mice was placed on a 14-day regimen of 20 mg of calf thymosin per kg per day, and the growth of the BCG in the lungs, spleen, inguinal lymph node, bone marrow, and blood was determined for up to 90 days. The thymosin treatment was followed by a decline in the BCG counts for the lungs and spleens of the THXB mice, whereas the saline-treated controls showed no such decline with time. The thymosin-treated mice did not develop progressive BCG infections in the test lymph nodes or in the bone marrow, both of which became positive in the THXB mice. Spleen cells were harvested from thymosin-treated THXB donors, filtered through nylon wool, and infused 3 times into BCG-infected THXB recipients. The lung BCG counts declined approximately 10-fold by day 90 compared with THXB mice which received THXB spleen cells. The transferred immune response was only slightly smaller numerically than that seen in THXB mice infused with BCG-immune lymphocytes from normal donors.