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Thymosin Alpha-1 vs. TB-500: Thymosin Family Comparison

Thymosin Alpha-1 and TB-500 both carry the ‘thymosin’ name and both were originally isolated from thymus tissue, but they are structurally and functionally unrelated. Thymosin Alpha-1 is a 28-amino-acid peptide with immunomodulatory research history. TB-500 is a 17-amino-acid fragment of the actin-binding protein Thymosin Beta-4. Same family name, different chemistry.

Published July 28, 2026 · Reviewed by Dr. Marina Voss, PhD (Senior Research Reviewer)

Quick comparison

 Thymosin Alpha-1TB-500 (Thymosin Beta-4 fragment)
Parent peptideThymosin α1 (full sequence 28 aa)Thymosin β4 (full sequence 43 aa); TB-500 is a 17-aa fragment
Amino-acid length2817 (as sold research fragment)
Molecular weight~3108 Da~1717 Da
Regulatory statusApproved as Zadaxin in select countries for adjunct antiviral / immune contextsInvestigational research compound; no regulatory approval
Primary studied mechanismTLR2/TLR9 activation, T-cell maturation modulationG-actin sequestration, wound-healing pathway research
Most-cited research contextImmune-response research, viral-adjuvant preclinical workMusculoskeletal repair, vascular remodeling research
Verdict: Same family label, different tools. Thymosin Alpha-1 belongs to the alpha-thymosin peptide family and shows up in immune-modulation research. TB-500 is a shortened fragment of Thymosin Beta-4 and shows up in actin-binding and tissue-remodeling research. Choose based on the target pathway.
Buy Thymosin Alpha-1 →Buy TB-500 (Thymosin Beta-4 fragment) →

Why both are called ‘thymosin’

The thymosin family is a collection of peptides originally purified from thymus extract in the 1960s. Later work showed the extract contained multiple structurally unrelated peptides which were sub-classified as alpha, beta, and gamma thymosins by isoelectric point. The alpha-thymosins share sequence homology with each other; the beta-thymosins share sequence homology with each other; alpha and beta thymosins are unrelated at the sequence level. Thymosin Alpha-1 is the most studied alpha-thymosin; Thymosin Beta-4 (from which TB-500 is derived) is the most studied beta-thymosin.

What the research covers

Thymosin Alpha-1 research has focused on immunomodulation — TLR signaling, T-cell maturation, and adjuvant contexts. It carries regulatory approval as Zadaxin in over 30 countries for specific therapeutic indications. TB-500 research has focused on actin binding, cell migration, and tissue-repair models including cardiac, tendon, and corneal wound-healing studies in rodents. Both are commonly cited in review articles but their bodies of literature don’t overlap much.

Frequently asked questions

Quick answers about the Thymosin Alpha-1 vs TB-500 (Thymosin Beta-4 fragment) comparison.

Is TB-500 the same as Thymosin Beta-4?+

TB-500 is a research fragment of Thymosin Beta-4 — specifically the C-terminal 17-amino-acid region containing the actin-binding motif. It is not the full-length TB4 protein.

For laboratory research use only. Not for human or veterinary use. Content is informational and does not constitute medical advice.