an ornamented digest of the thymic peptide literature
Thymulin is the zinc-bound thymic nonapeptide that early metallochemistry first named in 1982.
A faithful, finely-kept reading of the published record — the nine-residue sequence, the single bound zinc on which its activity turns, the dated and sparse human evidence, and how it differs from the peptides it is forever mistaken for.
The short version
Thymulin is a small hormone made by the thymus — the immune-training gland that sits behind the breastbone. It is a nonapeptide (a chain of nine amino-acid building blocks), and its single defining fact is that it only switches on when one atom of zinc is attached to it; strip the zinc away and it goes silent. It was first isolated as serum thymic factor and given the name thymulin in 1982, once researchers proved the active form was the zinc-bound one [1]. This site is an editorial digest: it summarizes what the studies actually measured, in animals, cells, and a thin set of dated human reports — not a course of treatment, not a product.
What the thymulin record has established
Thymulin is a zinc-dependent thymic nonapeptide hormone, produced by thymic epithelial cells (the gland's lining cells that build the hormone), and biologically active only as the zinc-bound complex [1][2]. Its canon is small and old: a French-coined molecule — serum thymic factor, facteur thymique sérique — characterized through the metallochemistry of the late 1970s and 1980s, with a handful of dated human reports and one modern line of gene-therapy work [4][5].
The single most-cited result is the one that named it. In 1982, stripping the bound metal from serum thymic factor with a chelator abolished its activity in a cell assay; adding zinc back restored it, best at a one-metal-to-one-peptide ratio. The authors proposed the name thymulin for the zinc-bound active form [1]. Everything downstream — the immune work, the anti-inflammatory work, the neuroendocrine work — rests on that fact: thymulin is the zinc-bound form, and the zinc-free apopeptide does nothing until the metal returns.
The rest of this digest reads the record by tissue and by claim: the thymulin research findings in immune, anti-inflammatory, and neuroendocrine models; the thymulin dosage in research reported by species and route; the thymulin side effects the sparse human literature does and does not describe; and thymulin and hair loss, the single preliminary topical pilot. A standing caution rides every page: thymulin is not FDA-approved, the human data are dated and sparse, and it is not the same molecule as thymosin alpha-1 or thymalin.
Thymulin peptide: identity and structure
The thymulin peptide is a linear nonapeptide with the sequence pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (written <Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn), carrying a molecular weight near 858.86 Da and the CAS number 63958-90-7 [2]. It is registered under PubChem CID 3085284 and FDA UNII 9H198D04WL. Nine residues, one bound zinc — the whole molecule is, in effect, a single metal node set in a short peptide chain.
Its production is anatomically narrow. Thymulin is secreted by thymic epithelial cells and by no other tissue; it circulates from birth, peaks in childhood, and declines with age and with zinc deficiency [4][11]. A cross-sectional human study of thymulin titres across the lifespan documented exactly this arc — high in children, falling progressively from adolescence into low levels in older adults [11].
The synonyms matter, because they are where the confusion starts. Serum thymic factor (FTS) is the original name for the same peptide; thymulin was coined specifically for the zinc-bound, active form [1]. A synthetic analog, nonathymulin, appears in several of the older human trials in place of the native peptide [7]. None of these names are thymosin alpha-1, and none are thymalin — distinct molecules covered on the research page.
The role of zinc in thymulin activity
Zinc thymulin is not a formulation; it is the molecule itself in its working state. Thymulin's biological activity depends entirely on binding one zinc ion per peptide, in a 1:1 molar ratio [1][2]. The zinc-bound form adopts a specific three-dimensional conformation — detectable by NMR — that the zinc-free apopeptide does not [2]. Chelating the metal switches the activity off; restoring zinc switches it back on.
This dependence is so tight that serum thymulin activity behaves as a readout of zinc status. In humans with mild zinc deficiency, thymulin activity fell even while plasma zinc looked normal, and was corrected by zinc repletion both in the body and in the test tube — alongside reversible shifts in T-cell subsets [3]. Zinc, in other words, is not a cofactor thymulin happens to use. It is the switch. Every reported effect of thymulin is, strictly, an effect of the zinc-bound complex, which is one reason thymulin-specific outcomes are difficult to disentangle from zinc status — a caveat carried throughout this digest.
What is thymulin?
What is thymulin?
Thymulin is a zinc-dependent thymic nonapeptide hormone — sequence pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn — made exclusively by thymic epithelial cells and biologically active only when bound to zinc in a 1:1 ratio [1][2]. It is studied as a research peptide; it is not FDA-approved for any use and is not a dietary supplement.
What does thymulin do in the body?
Endogenously, thymulin drives T-lymphocyte differentiation (the maturation of the immune system's trained defender cells into working subsets) and acts as a hypophysiotropic peptide — one that signals to the pituitary — within a two-way thymus-neuroendocrine axis [4]. In study models it also shows anti-inflammatory activity, partly by damping NF-kB, a master switch that turns inflammation genes on [6]. These are described findings in research models, not demonstrated human treatments.
Is thymulin the same as serum thymic factor (FTS)?
Yes. FTS — facteur thymique sérique, serum thymic factor — is the original name. The term thymulin was coined for the zinc-bound, biologically active form of that same peptide once the zinc requirement was established [1].