Thymulin is a naturally occurring nonapeptide first isolated from porcine blood serum in the early 1970s and formally characterized in 1977 by immunologists Jean-François Bach and Mireille Dardenne at the Institut Necker in Paris. Originally designated Facteur Thymique Sérique (FTS), it was renamed thymulin in 1981. The peptide derives exclusively from thymic epithelial cells and carries an N-terminal pyroglutamic acid residue. Its defining property is an absolute requirement for equimolar zinc (Zn²⁺) binding — without the zinc cofactor, the peptide is biologically inert, making thymulin the only known thymic hormone dependent on a metal ion for activity.

Research conducted primarily by Dardenne, Bach, and later by Goya and colleagues at CONICET (Argentina) has characterized thymulin across a range of preclinical models. Investigated areas include T-lymphocyte maturation and differentiation marker induction (CD2, CD3, CD4, CD8), neuroendocrine-thymic axis signaling, age-related immunosenescence and thymic involution, NK cell activity modulation, and inflammatory pain pathways. All findings referenced here derive from preclinical models and have not been validated in controlled human clinical trials.

Thymulin research appears in Annals of the New York Academy of Sciences, International Immunopharmacology, and Neuroscience. The compound is not approved by the U.S. Food and Drug Administration for any therapeutic indication. It is classified as a research compound only.