Thymus Peptides Explained: Thymosin Alpha-1, Thymulin, Thymogen and Thymalin

The thymus is where the immune system’s T cells learn their job, and it is one of the first organs to age. From the 1960s onward, laboratories in New York, Paris and Leningrad went looking for the molecules it releases. What they found ranges from a well-characterized 28-amino-acid peptide approved as a medicine abroad, to a zinc-dependent hormone, to dipeptides and a crude tissue extract.

This guide maps the thymus peptides on research shelves today: what each one is, where it came from, how strong its evidence is, and what to check when you source it.

The short answer

• The thymus shrinks with age, a process called thymic involution, which reduces the output of new T cells. That decline drove decades of research into thymic peptides.
• Thymosin alpha-1 is a defined 28-amino-acid peptide first isolated from calf thymus in 1977. It is approved as thymalfasin in a number of countries, though not in Canada.
• Thymulin is a nine-amino-acid hormone made by thymic epithelial cells. It is only active when bound to zinc, and its blood levels fall with age and with zinc deficiency.
• Thymogen (Glu-Trp) and Vilon (Lys-Glu) are dipeptides from the Russian bioregulator tradition, studied mainly in that research community.
• Thymalin is not a single peptide but an extract of calf thymus, with human data coming largely from one research group.

The thymus, and why it shrinks

The thymus sits behind the breastbone. Immature T cells travel there from the bone marrow and are trained: cells that can recognize threats are kept, and cells that would attack the body’s own tissues are eliminated. The thymus begins to shrink early in life, and the process accelerates after puberty, as functional tissue is gradually replaced by fat. Output of new naive T cells falls with it, one reason immune responses tend to weaken with age.

That decline raised an obvious question: does the thymus release signalling molecules that could be identified, measured and studied? Several research groups set out to answer it.

A family of thymus peptides

The molecules that came out of that search differ enormously in size and in how well they are defined.

The New York laboratory of Allan Goldstein and Abraham White produced thymosin fraction 5, a partially purified calf-thymus extract, from which thymosin alpha-1 was later isolated. In Paris, Jean-François Bach’s group identified a thymic factor in blood serum that became thymulin. Gideon Goldstein’s team defined thymopentin, a five-amino-acid fragment of the thymic protein thymopoietin. In Leningrad, Vladimir Khavinson and colleagues developed the extract thymalin, from which the dipeptide thymogen was later derived.

Thymosin alpha-1

Thymosin alpha-1 is a 28-amino-acid peptide, N-acetylated at its start, isolated from calf thymus in 1977. Under the name thymalfasin it is approved in a number of countries, mainly for chronic hepatitis B and as an immune adjunct, and it is studied for its effects on T-cell maturation and on dendritic cells through Toll-like receptors. It is not authorized in Canada or the United States. Our thymosin alpha-1 guide covers its trial record in detail.

Thymulin, the zinc-dependent hormone

Thymulin, once called facteur thymique sérique (serum thymic factor), was described by Bach’s group in 1977. It is a nonapeptide, pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, made by thymic epithelial cells, and it is biologically active only when bound to zinc in a one-to-one complex. That dependence makes thymulin unusual: in experimental animals and in people, mild zinc deficiency lowers its measured activity, and zinc repletion restores it.

Researchers have studied thymulin’s role in T-cell differentiation, its decline with age, and its links with the nervous and endocrine systems, including anti-inflammatory and pain-related effects in animal models. There is no approved thymulin medicine.

Thymogen and Vilon

Thymogen is the dipeptide glutamyl-tryptophan (Glu-Trp), identified in Russia in the 1980s as an active fragment of thymalin and studied there for decades as an immune modulator. Vilon, lysyl-glutamate (Lys-Glu), comes from the same St. Petersburg bioregulator programme and is often used as its reference compound. Both are tiny molecules, around 333 and 275 g/mol respectively.

The evidence for both comes overwhelmingly from one research tradition, much of it published in Russian, with little independent replication. Our Pinealon guide explains how that bioregulator programme works and how to weigh its claims. See Thymogen and Vilon.

Thymalin, the extract

Thymalin is not a defined molecule. It is a complex of peptides extracted from calf thymus, developed in Leningrad in the 1970s. Because its composition is a mixture, two batches can’t be verified against a single sequence and mass the way a synthetic peptide can, and its human results come largely from the group that developed it. Pure Peptides Canada does not stock thymalin.

Side by side

Verifying thymus peptides

• Identity by mass spectrometry. Thymulin should show the free peptide at about 859 g/mol; the zinc complex usually comes apart under analytical conditions. Thymosin alpha-1 should include its N-terminal acetyl group. See how to read a peptide mass spectrum.
• The zinc question. Check whether thymulin is supplied as the free peptide or as a zinc complex, since activity depends on it.
• Purity by HPLC, with the chromatogram. For immune-cell work, also consider endotoxin.
• A lot number matching your vial. See our COA guide.

Frequently asked questions