Effect of Thymosin α₁ on Immunoregulatory T Lymphocytes

Abstract

The extensive work performed by A. L. Goldstein and co-workers has led to the isolation, chemical characterization, and biological and clinical applications of thymosins present in “fraction 5,” a partially purified extract from bovine thymus (Hooper et al., 1975). Fraction 5 consists of 40–50 peptides whose molecular weights range from 1000 to 15,000, as demonstrated by analytical Polyacrylamide gel electrophoresis and isoelectric focusing (Goldstein et al., 1977). Some of these peptides exhibit a wide range of biological activities in animal models (Goldstein, 1978). It has been established that there is no homology between the biologically active thymosin peptides and thymopoietin (Goldstein, 1975) or facteur thymique sérique (Bach and Dardenne, 1972). Among the several peptides present in fraction 5, α₁ was the first to be purified, sequenced (Goldstein et al., 1977), and synthesized (Goldstein, 1978). It is a highly acidic molecule, consisting of 28 amino acid residues. Several tests performed both in vivo and in vitro have shown that α₁ is 10–1000 times more active than fraction 5 in promoting T-cell differentiation. It has been found that in vivo administration of α₁ enhances the lymphoid cell responses to mitogens as well as lymphotoxin production (Schulof and Goldstein, 1983). Results of α₁ treatment in conjunction with intensive conventional chemotherapy show that growth of plasmacytoma MOPC-315 in Balb/c mice is reduced or prevented. Moreover, the surviving animals reject retransplanted tumor cells (Goldstein et al., 1983).