# Thymulin: A Field Atlas of the Zinc-Bound Thymic Peptide

> Thymulin is a zinc-dependent thymic nonapeptide active only when it holds a single zinc ion. A cited literature digest of the published research, read straight.

A species dossier for a vanishing hormone - the discovery that named it, the studies that measured it, and the human-data gaps marked plainly, every quantitative claim cited.

## The short version, in plain words

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 has one defining trick: it only switches on when a single atom of zinc is clamped onto it. No zinc, no activity. The body carries thymulin from birth, it crests in childhood, and it thins out again with age and with low zinc. Scientists have studied it for fifty years in cells and animals - for the immune system, for inflammation, for pain, and lately through gene therapy. It is a research peptide. It is not an FDA-approved drug, and it is not a dietary supplement.

## What the thymulin literature is, and what this atlas does

Thymulin was named in 1982, when researchers showed that the serum thymic factor lost all activity once zinc was stripped from it and regained that activity when zinc was added back at exactly one metal ion per peptide [1]. That single fact - alive only while it holds its zinc - is the spine of everything that follows.

This site reads the thymulin record the way a naturalist reads a fading species: every study catalogued as a specimen, the lush findings the literature genuinely establishes set beside the scorched gaps it has never filled. Thymulin is produced exclusively by thymic epithelial cells (the gland's lining cells that build the peptide), it circulates from birth, peaks in childhood, and declines with age and zinc deficiency as the thymus involutes [4]. A hormone, in other words, that thins out of the body the way a population thins out of a habitat.

What the published work covers is broad and almost entirely preclinical: T-cell biology, anti-inflammatory signaling, neuroinflammation and pain, a thymus-pituitary axis, and an experimental gene-therapy literature that tries to re-seed the peptide once it has waned [4][5]. What it does not cover is large modern human efficacy trials, an established human dose, or a worked-out human half-life. Both columns are kept visible here. [Why thymulin needs zinc](/zinc-dependence) is the right place to start; the [thymulin research findings](/research) follow.

## Thymulin Peptide: Structure and Identity

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), molecular formula C33H54N12O15 and a molecular weight near 858.86 Da [2]. Its catalogue identifiers are CAS 63958-90-7 and FDA UNII 9H198D04WL. These specimen marks matter because the field is crowded with look-alikes, and the exact sequence is what tells thymulin apart from them.

The peptide alone is not the active molecule. Biological activity requires one zinc(II) ion bound in a 1:1 molar ratio; the zinc-bound form adopts a specific three-dimensional shape detectable by NMR, and the zinc-free apopeptide is inactive [2]. So the honest name for the active species is zinc-thymulin, and the term thymulin in this atlas always means the metal-bound, biologically active form unless a study is explicitly describing the apopeptide.

## Is thymulin the same as serum thymic factor (FTS)?

Yes, in lineage. Serum thymic factor - FTS, from the French facteur thymique serique - is the original name for the same peptide. FTS denotes the zinc-free peptide; once zinc binds at a 1:1 ratio, the active complex was christened thymulin (FTS-Zn) [1]. So FTS and thymulin are two states of one molecule: the apo form and the zinc-loaded, switched-on form. Serum thymulin activity, measured historically by a rosette bioassay, falls with zinc deficiency and is corrected by zinc repletion, which is why thymulin activity reads as a sensitive indicator of zinc status [2].

## What thymulin does in the body

Endogenously, thymulin's classical role is in T-cell biology: it drives T-lymphocyte differentiation (the maturation of T cells, the immune system's trained defender cells, into functional subsets) and modulates immune-cell function through specific high-affinity receptors on T-lineage cells [4]. Beyond immunity, it behaves as a hypophysiotropic peptide - one that signals to the pituitary - inside a bidirectional thymus-neuroendocrine axis, and it carries anti-inflammatory activity linked in part to suppression of NF-kB, a master switch that turns inflammation genes on [4][6].

These are descriptions of a research-model and physiological record, not claims of a benefit in people. The most reliable way to read thymulin is as a zinc-dependent thymic hormone whose level marks the health of the thymus and the body's zinc economy, and whose decline tracks immunosenescence - the slow weakening of the immune system with age [4][14]. The studies that establish each piece are catalogued in the [thymulin research findings](/research).

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A deep-water field atlas of the thymulin literature - the zinc-bound thymic peptide catalogued like a vanishing species, the established findings pressed beside the human-data gaps and the molecule kept distinct from thymosin alpha-1 and thymalin; no clinic behind the specimen sheet and nothing here dosed, prescribed, or sold.