Immunological enhancement with a low dose of cyclophosphamide in aged mice

Aged mice treated with a low dose of cyclophosphamide (CY) showed significa ntly enhanced immune capacity in cellular proliferation and antibody respon se. In these mice, total cell numbers were increased both in the thymus and spleen, compared to those in non-treated mice. Treatment with a low dose o f CY induced apoptosis of thymocytes in the atrophic thymus of the aged mic e, being followed by an increase of proliferation of thymocytes and leading to an increase of thymocytes and splenic T cells. Treatment with a high do se of CY also induced apoptosis in the thymus, but suppressed the prolifera tive capacity, therefore not leading to an enhancement of immune capacity. In young mice, however, CY suppressed immune capacity regardless of the dos e. Thymocytes and splenic T cells of young mice were more susceptible to CY than those of old mice and were decreased in number after the treatment wi th even a low dose of CY. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.