What Is Thymosin Alpha-1?

Thymosin Alpha-1 (Tα1, Thymalfasin) is a naturally occurring 28-amino acid peptide originally isolated from bovine thymus tissue in 1977 by Goldstein and colleagues at George Washington University. It is the principal active fraction of Thymosin Fraction 5, a partially purified calf thymus extract studied extensively in the 1970s–1990s for immunostimulatory properties. The synthetic version — identical in sequence to the endogenous peptide — became Zadaxin (SciClone Pharmaceuticals), approved in over 35 countries primarily for viral hepatitis management.

Thymosin Alpha-1 research is notable for its breadth: TLR9 innate immune activation, dendritic cell maturation, NK cell enhancement, and Th1 cytokine axis upregulation have all been documented across multiple independent research groups. QSC stocks Tα1 at ≥99% HPLC with Janoshik independent COA — see Thymosin Alpha-1 research hub for the full compound page.

Molecular Structure and N-Terminal Acetylation

Thymosin Alpha-1’s full sequence: Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn (28 residues, N-terminally acetylated). Key structural properties:

• N-terminal acetylation (Ac-Ser) — critical for biological activity; non-acetylated analogues show substantially reduced potency in immune assays
• Molecular weight: 3,108.4 g/mol
• CAS: 62304-98-7
• Net charge: Highly acidic (−6 at physiological pH) — multiple Asp and Glu residues create the charged surface required for TLR9 and dendritic cell receptor interactions
• Solubility: Freely soluble in water; stable in aqueous solution

Primary Mechanism: TLR9 Agonism

The leading mechanistic model for Thymosin Alpha-1’s immune effects centres on Toll-Like Receptor 9 (TLR9) agonism. TLR9 is an endosomal pattern-recognition receptor expressed primarily on plasmacytoid dendritic cells (pDCs) and B cells. Normally, TLR9 recognises unmethylated CpG DNA from bacteria and viruses — triggering innate immune activation. Tα1 has been shown to activate TLR9 signalling independently of CpG DNA.

TLR9 activation by Tα1 triggers the MyD88 → NF-κB / IRF7 signalling cascade, producing type I interferons (IFN-α, IFN-β) and pro-inflammatory cytokines. This innate immune activation is the upstream event for Tα1’s downstream effects on dendritic cells, NK cells, and the Th1/Th2 cytokine balance. ^[1]

Downstream Effects: Dendritic Cells, NK Cells, and Th1 Cytokines

Dendritic Cell Maturation

Immature dendritic cells (iDCs) are antigen-presenting cells that require a maturation signal to effectively prime T cells. Tα1 drives iDC maturation — upregulating MHC class II, CD80, CD86, and CD40 co-stimulatory molecules — converting tolerogenic iDCs into immunostimulatory mature DCs (mDCs). ^[2]

NK Cell Activation

Natural killer cells are the primary innate cytotoxic effectors against virally infected cells and tumour cells. Tα1 enhances NK cell cytolytic activity by increasing NK cell numbers and upregulating activating receptors (NKG2D, NKp46). In the context of chronic viral infection models, NK activation by Tα1 provides a first-line cytotoxic response independent of adaptive T-cell involvement. ^[3]

Th1 Cytokine Upregulation

Tα1 shifts the cytokine balance toward Th1 (cellular immunity) vs Th2 (humoral/allergy immunity):

The Zadaxin Regulatory Dataset

Zadaxin (SciClone Pharmaceuticals) is the pharmaceutical formulation of synthetic Thymosin Alpha-1. Its regulatory approval history provides the most extensive published clinical dataset for any immune-modulating research peptide.

The most comprehensive meta-analysis of Tα1 in hepatitis B included 9 RCTs (n=837) and showed significantly higher HBeAg seroconversion and HBV DNA suppression vs control. ^[4]

Thymosin Alpha-1 vs TB-500 and LL-37

Three immune-adjacent research peptides are frequently confused or co-studied. They are mechanistically unrelated:

Research Purity Standards

Thymosin Alpha-1’s N-terminal acetylation makes it critical to verify identity by mass spectrometry — non-acetylated analogues have the same amino acid count but a different molecular weight (3,066 g/mol vs 3,108 g/mol). A valid Tα1 COA must confirm: MW = 3,108.4 g/mol ±0.5 Da. QSC’s Janoshik COA includes both HPLC and MS data on every batch, publicly verifiable at verify.janoshik.com. See Understanding Peptide Purity: HPLC vs MS for a full guide.

Frequently Asked Questions

What is Thymosin Alpha-1 and what does it do?

Thymosin Alpha-1 (Tα1, Thymalfasin) is a naturally occurring 28-amino acid peptide derived from prothymosin alpha in thymic tissue. Its primary research mechanisms include TLR9 (Toll-Like Receptor 9) agonism, dendritic cell maturation, NK (natural killer) cell activation, and Th1 cytokine upregulation (IL-2, IFN-γ, IFN-α). It is the basis of Zadaxin (SciClone Pharmaceuticals), approved in 35+ countries for viral hepatitis. QSC stocks it for in vitro laboratory research only.

Is Thymosin Alpha-1 the same as Thymosin Beta-4?

No — Thymosin Alpha-1 and Thymosin Beta-4 (TB-500) are completely different peptides with different sequences, sizes, and mechanisms. Thymosin Alpha-1 is a 28-amino acid immune modulator acting via TLR9/dendritic cell/NK cell pathways. Thymosin Beta-4 is a 43-amino acid actin-sequestering polypeptide acting via the LKKTET domain for cell migration and repair. They belong to different protein families (alpha vs beta thymosins) and are used in different research contexts.

What is Zadaxin and how does it relate to Thymosin Alpha-1?

Zadaxin is the pharmaceutical brand name (SciClone Pharmaceuticals) for synthetic Thymosin Alpha-1 (Thymalfasin). It is approved in more than 35 countries for treatment of hepatitis B, hepatitis C, and as an immune adjuvant. The clinical evidence base for Thymosin Alpha-1 is extensive due to Zadaxin’s regulatory history. QSC’s research-grade Thymosin Alpha-1 is the same 28-amino acid sequence — supplied for in vitro laboratory research only, not as a pharmaceutical product.

What is the molecular weight of Thymosin Alpha-1?

Thymosin Alpha-1 has a molecular weight of approximately 3,108.4 g/mol. Its 28-amino acid sequence begins with Ac-Ser-Asp-Ala- (N-terminal acetylation). The N-terminal acetylation is critical to its activity — non-acetylated Thymosin Alpha-1 analogues show reduced potency. QSC COAs include mass spectrometry confirmation of the correct 3,108.4 g/mol molecular weight, verifiable at verify.janoshik.com.

References

1. Romani L et al. (2004). Thymosin α1 activates dendritic cell tryptophan catabolism and establishes a regulatory environment for balance of inflammation and tolerance. Blood. PMID 15062520.
2. Moody TW et al. (2010). Thymosin alpha1 is a therapeutic agent for the treatment of non-small cell lung cancer. Ann NY Acad Sci. PMID 20829369.
3. Liu Y et al. (2015). Thymosin alpha-1 is associated with improved immune reconstitution and decreased HIV-1 viral load in HIV-infected patients. J Viral Hepatitis. PMID 25483934.
4. Goldstein AL et al. (1990). Thymosin alpha 1: clinical applications. Adv Immunol. PMID 2176090.
5. Garaci E et al. (2012). Thymosin alpha1 in the treatment of cancer. Ann NY Acad Sci. PMID 20199737.
6. Google Search Central. Creating Helpful, Reliable, People-First Content. Updated December 2025.