Immunopharmacology. I1 (1986) 155-163 Elsevier 155 IMO 00321 Reconstitution of T Cell Functions in Aging Mice by Thymosin al Daniela Frasca, Luciano Adorini, Camillo Mancini and Gino Doria ENEA-Euratom Immunology Group, Laboratory of Pathology, C.R.E. Casaccia, C.P. 2400, 00100 Rome A.D., Italy (Received 26 November 1985; accepted 2 January 1986) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR Abstract: Helper T cell activity of spleen cells from BDFl mice is impaired by aging but is restored to a large extent by injection of thymosin al, a synthetic peptide consisting of 28 amino acid residues. Injection of an equimolar amount of the N1., (N-terminal half of thymosin ccl) synthetic fragment is at least as effective as the entire a1 molecule in increasing helper T cell activity of spleen cells from old (618 months) mice but not from young (3 months) mice. Conversely, injection of the Cl4 (C-terminal half of thymosin al) synthetic fragment is devoid of any effect in both young and old mice. Since helper T cell activity of spleen cells from old mice is also increased by injection of interleukin-2, the observed enhancement of interleukin-2 production by mitogen-activated spleen cells from old mice upon injection of thymosin a1 or the N 14 fragment suggests that these peptides amplify helper T cell activity by increasing the cell precursor frequency of interleukin-2-producing T cells. This conclusion is further supported by the finding that injection of thymosin CI~, or its N14, but not C14r fragment enhances the expression of interleukin-2 receptors on mitogen-activated spleen cells from old but not from young mice. Key words: Aging; Thymic factors; Helper activity; Interleukin-2 production; Interleukin-2 receptor Introduction Antibody responses to a variety of exogenous an- tigens decrease with aging, as a result of changes occurring primarily in the T cell compartment of the immune system (Makinodan and Kay, 1980). Profound defects in T cell functions have been de- tected in old animals and attributed to thymus in- volution (Hirokawa and Makinodan, 1975) and subsequent reduced concentrations of circulating thymic factors required for T cell maturation (Goldstein et al., 1981). During the past few years we have investigated the possibility of restoring decreased T cell func- tions in old mice by injection of thymosin al, a syn- thetic peptide consisting of 28 amino acid residues (molecular weight 3 108). Thymosin CI~ has been obtained by solid phase synthesis (Wang et al., 1979) after purification and sequence analysis (Low and Goldstein, 1979) of the peptide obtained from the calf thymus extract Fraction 5 (Hooper et al., 1975). Several experimental animal models and clinical trials have shown the important role of syn- thetic thymosin CI~ in promoting T cell maturation (Zatz et al., 1982; Schulof and Goldstein, 1983). We have previously shown that injection of immuno- deficient old mice with thymosin al is able to restore to a large extent defects in helper activity of spleen cell populations (Frasca et al., 1982) and of nylon wool-fractionated T cell subpopulations Doria et al., 1984a, 1984b; Frasca et al., 1985). In the present study, aging (3-18 month old) mice have been used to investigate the effect of injecting thymosin al, its N14 (N-terminal amino acid resi- dues 1-14) or Cl4 (C-terminal amino acid residues Abbreviations: BSS, balanced salt solution; Con A, Concana- valin A; FCS, fetal calf serum; HRBC, horse red blood cells; IL-2, interleukin-2; 2-ME, 2-mercaptoethanol; PBS, phosphate buffered saline; PFC, plaque forming cells, PMA, phorbol myr- istic acetate; RARIg, rabbit anti-rat Ig; rHuIL-2, recombinant human IL-2; RIA, radioimmunoassay; RIAB, RIA buffer; SRBC, sheep red blood cells; TNP, 2,4,6_trinitrophenyl. 0162-3109/86/$03.50 0 1986 Elsevier Science Publishers B.V. (Biomedical Division)