Modulation of terminal deoxynucleotidyl transferase activity by thymosin

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Abstract
Thymosin fraction 5, a family of acidic polypeptides isolated from bovine thymus, contains several hormonal-like factors which have been shown to influence the maturation, differentiation and functions of T-cells. Some of these peptides have been chemically defined. Two of them, thymosin α1 (M.W. 3108) and thymosin β4 (M.W. 4982) have been sequenced. In murine systems, terminal deoxynucleotidyl transferase (TdT) has been shown to be T-cell specific and to be present primarily in the cortisone sensitive immature T-cell populations. The daily injection of thymosin fraction 5 and two of its components, thymosin β3 and β4, significantly increases TdT activity in immune suppressed mice as compared to control groups. This study indicates that thymosin can act on prothymocytes and influence the early stages of T-cell differentiation. In an in vitro system, thymosin fraction 5 and the purified peptide, thymosin β1, have high activities in decreasing TdT in normal murine thymocytes after a 22-h incubation. This effect suggests that thymosin can also act on thymocytes and regulate the later biochemical processes during T-cell differentiation.

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