Restoration of immunocyte functions by thymosin α1 in cyclophosphamide-induced immunodeficient mice

Thymosin α1 (Tα1) is an oligopeptide hormone originally isolated from the thymus gland, and has been reported to have stimulating effects on the differentiation of T cells and NK cells. These immunostimulating properties have been considered to be useful for improving immune disorders associated with various diseases including cancer, AIDS and hepatitis. Here, we characterized immunostimulating properties of Tα1 in experimental immunodeficiency of mice that was induced by the administration of cyclophosphamide (CY). Repeated injection of 30-300 μg/kg/day of Tα1 after CY-treatment significantly accelerated the restoration of the reduced number of CD4⁺CD8⁺ T cells in the thymus. Tα1 administration was effective in restoring the suppressed activities of helper T cells and cytotoxic T cells in CY-treated mice. Tα1 also had stimulating effects on reduced activity of lymphokine-activated killer cells in CY-treated mice. These results indicate that Tα1 is stimulatory for both humoral and cellular immune responses, thus providing the immunological basis for the clinical benefit of this compound.