Research digest · Zinc-bound thymic factor
Thymulin is a zinc-bound thymic nonapeptide, read here through its neuroendocrine axis.
A literature reference to the sequence, the zinc-dependent mechanism, the thymus–pituitary signaling, and the precise point where the human data stop. Every quantitative claim is keyed to a study.
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 one zinc atom is attached to it. Researchers have studied thymulin for how it helps T cells (the immune system's trained defender cells) mature, how it quiets inflammation, and how it talks to the brain's hormone-control center, the pituitary gland. Everything below is a digest of what published studies measured, in cells and in animals, with a little dated human data. Thymulin is a research peptide, not an FDA-approved drug, and this page does not give dosing advice.
What is thymulin?
Thymulin is a zinc-dependent nonapeptide hormone produced exclusively by thymic epithelial cells — the thymus gland's lining cells that build the molecule. Its biological activity depends entirely on binding one zinc ion per peptide molecule in a 1:1 ratio; the zinc-free form is inactive [1][2]. The name thymulin was coined specifically for this zinc-bound active state. In its original literature the peptide was called serum thymic factor, or FTS (facteur thymique sérique), and the active complex is written FTS-Zn or Zn-thymulin [1].
Thymulin circulates from birth, peaks in childhood, and declines with age and with zinc deficiency [2][4]. Because its activity tracks zinc status so closely, serum thymulin has been used as a sensitive functional indicator of zinc availability rather than as a marketed compound [2][3]. It is a research peptide: not FDA-approved for any use, not a dietary supplement, and handled as a laboratory chemical.
Thymulin is frequently confused, in consumer writing, with other thymic peptides. It is chemically and pharmacologically distinct from thymosin alpha-1 and from thymosin beta-4, and from the bovine thymic complex thymalin — different molecules, with different research literatures [9]. The thymulin vs thymosin alpha-1 distinction is drawn out in full on the research page; this site keeps those lines clean and reads only the thymulin record.
Thymulin Peptide: Structure and Identity
Thymulin (the thymulin peptide) is the linear nonapeptide pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn — written <Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, with a pyroglutamate residue (a cyclized N-terminal cap) at the front [2]. Its molecular formula is C33H54N12O15, with a molecular weight near 858.86 Da and CAS number 63958-90-7. The bound zinc ion is part of what makes the active molecule: nuclear magnetic resonance work shows that zinc binding induces a specific three-dimensional conformation, and the apopeptide (the zinc-free chain) does not adopt it [2].
That conformational switch is the defining mechanistic fact of the molecule, and it is the subject of why thymulin depends on zinc. The structural identity also explains why thymulin is studied as a metallopeptide — a peptide whose function is inseparable from its bound metal — rather than as a peptide that merely happens to need a cofactor.
What the research record covers
The thymulin literature runs along several parallel channels. The immune channel is the classical one: thymulin drives T-cell differentiation and modulates T-cell subset balance [2]. The anti-inflammatory channel is more recent: in lipopolysaccharide-challenged mice, thymulin lowered pro-inflammatory cytokines and modulated NF-kB (a master switch that turns inflammation genes on) and SAPK/JNK signaling [6]. The neuroendocrine channel is this site's editorial lens — thymulin acts as a hypophysiotropic peptide, signaling to the pituitary, and directly stimulated ACTH release from rat anterior pituitary cells in vitro, with a maximal effect near 10 pM [4][11].
A fourth, reproductive channel emerged from gene-therapy work: in congenitally athymic mice, an adenoviral vector expressing a synthetic thymulin analog preserved circulating gonadotropins and ovarian function [9][10]. These are research findings in their study species and models — described, not prescribed. Read them in full in the thymulin research findings, trace the signaling in thymulin and the neuroendocrine axis, and see the study doses in thymulin dosage in the literature.
What does thymulin do in the body?
Endogenously, thymulin is a thymic hormone: produced by thymic epithelial cells, it drives T-lymphocyte differentiation and helps set T-cell subset balance, and it participates in a bidirectional thymus–neuroendocrine loop [2][4]. In rat pituitary cells in vitro, zinc-bound thymulin directly stimulated ACTH release, evidence of a hypophysiotropic action [11]. Its own secretion is, in turn, regulated by the neuroendocrine system [4].
Is thymulin produced naturally in the body?
Yes. Thymulin is produced exclusively by thymic epithelial cells. It circulates from birth, peaks in childhood, and declines with age and with zinc deficiency [2][4]. Because production is concentrated in thymic tissue and depends on zinc, serum thymulin activity falls as the thymus involutes with age and as zinc status drops [2][3].
What is the amino acid sequence of thymulin?
Thymulin is the linear nonapeptide pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (<Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn), molecular formula C33H54N12O15, with a bound zinc ion required for activity [1][2]. The N-terminal pyroglutamate is a cyclized glutamine residue; the nine-residue chain is short even by peptide-hormone standards.