Immunomodulating activity of thymosin fraction 5 and thymosin ?1 in immunosuppressed mice

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Abstract
We found that both thymosin from calf thymus and its constituent peptide α1 prepared by chemical synthesis restore cell-mediated immunity following its suppression in mice by injection of 5-FU. Conditions suitable for assessing the thymosin activity by means of footpad reaction were established in such immunosuppressed mice. In this new animal model, thymosin α1-peptide showed activity at a low dose of 5–50 μg/kg, which was 100–1,000 times less than that required for thymosin F-5 preparations. Further studies utilizing the adoptive transfer technique showed that α1-peptide corrects the 5-FU-induced suppression of mature T cells, transferring the DTH response as well as that of macrophage function responsible for the expression of footpad reaction. Furthermore, regeneration of lymph node and bone marrow cells as well as CFU-c (progenitor cells of macrophages and granulocytes) was enhanced by thymosin α1 in the 5-FU-treated mice. All these results indicate that thymosin α1 accelerates the replenishment and maturation of haematopoietic cells, including not only T cells but also macrophages, when they have been severely damaged by the 5-FU treatment.