The study shows that calf thymus cells can naturally make the peptide thymosin‑alpha‑1, confirming it isn’t just an artificial lab product but is produced inside the body’s immune organ.

Thymus and thymocytes from calf were extracted under isotonic conditions in the presence of protease inhibitors or under severe denaturing conditions (after quick freezing and thawing in boiling 0.1 M NaCl). The extracts, as well as the medium in which the thymocytes were obtained from thymus fragments (thymocyte supernatants), were size-fractionated by ultrafiltration. As in whole thymus isotonic extracts, thymosin alpha 1 [A. L. Goldstein, T. L. K. Low, M. McAdoo, J. McClure, G. B. Thurman, J. Rossio, C-Y. Lai, D. Chang, S-S. Wang, C. Harvey, A. H. Ramel, and J. Meienhofer (1977) Proc. Natl. Acad. Sci. USA 74, 725-729] was contained in isotonic extracts from thymocytes and also in thymocyte supernatants, as determined by isoelectric focusing and reverse-phase HPLC analysis. The extraction under denaturing conditions mainly yielded products with molecular masses over 50,000, showing very similar isoelectric focusing patterns in both thymocytes and whole thymus extracts. As deduced by isoelectric focusing analysis of diverse size-fractionated products, a strong association capacity seems to be responsible for an apparently high molecular mass of the components of these extracts. According to the pI, two of these components were prothymosin alpha [A. A. Haritos, G. J. Goodall, and B. L. Horecker (1984) Proc. Natl. Acad. Sci. USA 81, 1008-1011] and thymosin alpha 1. Prothymosin alpha was not detected in any isotonic extracts or thymocyte supernatants. These data suggest that calf thymocytes are capable of producing thymosin alpha 1, which would arise by natural processing of its precursor.