Thymulin is a zinc-dependent thymic nonapeptide, biologically active only when one zinc ion is bound.

The short version

Thymulin is a small hormone made by the thymus (the immune-training gland behind the breastbone). It is a nonapeptide (a chain of nine amino-acid building blocks), and it only switches on when a single zinc atom is attached to it. Strip the zinc away and the molecule goes inert. Most of what is known comes from animal and cell studies: in those models thymulin helps T cells (the immune system's trained defender cells) mature, calms inflammation, and dampens pain signaling. It is not FDA-approved, not a supplement, and not the same molecule as thymosin alpha-1. This page is a plain-English map of that record.

What Is Thymulin?

Thymulin is a metallopeptide hormone produced exclusively by thymic epithelial cells (the gland's lining cells that build it) and biologically active only when bound to zinc in a 1:1 molar ratio ^[2]. Its molecular weight is 858.86 Da and its CAS number is 63958-90-7.

The defining fact is the zinc. In 1982, researchers treated the serum thymic factor with the chelator Chelex 100 — a resin that strips metal ions out of solution — and its biological activity vanished in the rosette assay. Adding zinc salts back restored it, with a 1:1 metal-to-peptide ratio giving optimal activation ^[1]. That experiment split the molecule into two named forms: a zinc-free, inactive peptide and a zinc-bound, active one. The active form is thymulin.

Endogenously, thymulin circulates from birth, peaks in childhood, and declines with age and with zinc deficiency ^[2]. Its classical job is driving T-lymphocyte differentiation — the maturation of T cells into functional subsets — but the literature also places it inside a two-way thymus-neuroendocrine axis, acting on the pituitary while the pituitary in turn regulates its production ^[4]. Everything below is read as study findings in named species, not as anything established in people.

Thymulin Peptide: Structure and Identity

The thymulin peptide is the linear nonapeptide pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, molecular formula C33H54N12O15 ^[2]. The first residue is a pyroglutamate (a cyclized, blocked N-terminus), which is one reason early purification of the molecule was difficult.

The sequence alone is not the active species. Zinc binding imposes a specific three-dimensional conformation — a precise fold — that the zinc-free chain does not adopt, and that fold is what the molecule's targets recognize ^[2]. This is the single most load-bearing fact about the compound, and it has its own page: thymulin zinc dependence.

Serum Thymic Factor (FTS): The Original Name. Thymulin was first described as facteur thymique serique — serum thymic factor, abbreviated FTS — the French name for the zinc-free peptide isolated from serum. When zinc binds, FTS becomes FTS-Zn, which the 1982 authors renamed thymulin ^[1]. So FTS, FTS-Zn, Zn-thymulin, and thymulin all name points on one molecule: FTS is the apo-form, thymulin is the zinc-loaded active form.

Is There a Thymulin Supplement? No. There is no marketed thymulin supplement and no FDA-approved thymulin product. Thymulin is handled as a research peptide for laboratory use, not as a dietary supplement and not as an approved drug. Consumer pages sometimes file it next to thymosin alpha-1 or thymalin (a bovine thymic complex); those are chemically and pharmacologically distinct compounds, and the conflation is an error this digest flags repeatedly ^[16].

Thymulin vs Thymosin Alpha-1: Distinct Peptides. Thymulin is a nine-residue, zinc-dependent peptide. Thymosin alpha-1 is a different, longer thymic peptide with its own sequence and pharmacology. They are not the same molecule, they are not interchangeable, and a study of one is not evidence about the other. This site never describes thymulin's research using thymosin alpha-1's data.

What the Numbers Show

Read the literature figure-first and a consistent picture appears. Serum thymulin activity tracks zinc status: in mildly zinc-deficient adults it fell despite normal plasma zinc and was corrected by zinc repletion ^[3]. In inflammation models, daily intraperitoneal thymulin at 1, 100, and 1000 ng produced dose-dependent reductions in hyperalgesia in mice, alongside lower skin IL-1beta and NGF after a 1 microgram dose ^[8]. In LPS-treated mice, two weeks of thymulin pretreatment lowered pro-inflammatory cytokines and modulated NF-kB and SAPK/JNK signaling ^[6]. And a single intratracheal dose of thymulin-expressing plasmids normalized key lung pathologies in established experimental asthma at 20 days ^[7].

The honest counterweight sits in the same paragraph as the finding. Thymulin alone did not change baseline pain thresholds — the anti-hyperalgesic effect appeared only against an inflammatory background ^[8]. There is no established human dosage and no validated human pharmacokinetic half-life in the public literature ^[2]. Several human studies used the synthetic analog nonathymulin, not native thymulin ^[15]. The full record, dose ladder, and caveats are on the thymulin research findings page, with the central-nervous-system work broken out under thymulin neuroinflammation and pain research.