Tuftsin

Tuftsin (Thr-Lys-Pro-Arg) is a natural tetrapeptide isolated in 1970 by Najjar and Nishioka at Tufts University from the heavy chain of immunoglobulin G (residues 289 to 292 of the Fc fragment). It is released enzymatically by leukokininase from splenic-cleaved IgG and stimulates phagocytosis, NK cell activity, and macrophage-mediated immune response. It is the parent peptide of the more drug-like analog Selank.

Overview

Tuftsin was identified during work characterizing the leukotactic activity of IgG fragments. The peptide is generated in vivo through a two-step proteolytic process: trypsin first cleaves the IgG heavy chain to release a 23-residue precursor, then a splenic enzyme (leukokininase) releases the active tetrapeptide. Splenectomy reduces circulating tuftsin levels, which is the basis for the partial immune compromise observed in asplenic patients.

Despite a clean mechanism and 50+ years of literature, tuftsin itself has not progressed to clinical use due to its very short plasma half-life (under 5 minutes) and oral bioavailability problems. Synthetic analogs including Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) extend the sequence with a stabilizing C-terminal tripeptide and have been studied in Russian clinical literature.

Mechanism

Tuftsin engages a high-affinity receptor on neutrophils, monocytes, macrophages, and NK cells (the tuftsin receptor or Nrp1-related complex per recent papers):

• Phagocytosis stimulation. Direct enhancement of opsonized and unopsonized phagocytosis by neutrophils and macrophages.
• NK cell activation. Increased cytotoxic activity against tumor cell targets in vitro.
• Macrophage activation. Cytokine release modulation (TNF-α, IL-1 in pro-inflammatory contexts; IL-10 in resolution contexts).
• Antimicrobial peptide release. Indirect effects via neutrophil degranulation.

See: Selank.

Evidence

Key publications:

• Najjar VA, Nishioka K. "'Tuftsin': a natural phagocytosis stimulating peptide." Nature. 1970;228(5272):672-3. [PMID 5479452](https://pubmed.ncbi.nlm.nih.gov/5479452/). (Discovery paper.)
• Siemion IZ, Kluczyk A. "Tuftsin: on the 30-year anniversary of Victor Najjar's discovery." Peptides. 1999;20(5):645-74. [PMID 10465517](https://pubmed.ncbi.nlm.nih.gov/10465517/).
• Khan A, Greenman J, Archibald SJ. "Small Molecule Theranostic Probes: A Promising Future in Neuroendocrine Tumor Theranostics." Curr Pharm Des. 2018;24(35):4189-4206. (Tuftsin-receptor-targeted imaging.)

Pharmacokinetics

Plasma half-life is under 5 minutes due to rapid proteolytic cleavage at the Lys-Pro and Pro-Arg bonds. This short half-life limited tuftsin's direct clinical utility and motivated the development of stabilized analogs like Selank and pegylated variants.

Dosing literature

Tuftsin itself has been studied in Phase 1 / 2 trials in cancer and immunodeficiency contexts at doses of 0.1 to 1 mg/kg intravenously. No FDA approval was pursued. This wiki does not recommend any human dose. Tuftsin is supplied as a research-grade chemical reference compound for in-vitro use only.

Storage

Lyophilized: 2 to 8 °C, stable 12+ months. Reconstituted: 2 to 8 °C, use within 14 days. The peptide is more stable as a lyophilized powder; aqueous solutions degrade faster than typical larger peptides. See Reconstitution.

Regulatory status

• United States. Not FDA-approved for any indication. Investigational / research-only.
• WADA. Not currently on the WADA Prohibited List as of the 2026 publication.
• Russia / former USSR. Tuftsin derivatives including Selank are used in clinical practice in Russia though not approved by Western regulators.

Side effects (from historical clinical literature)

Low toxicity profile in published Phase 1 work. Theoretical concerns:

• Possible exaggerated inflammatory response in subjects with autoimmune conditions
• Cross-talk with neutrophil function may interact with concurrent NSAID or immunosuppressant use
• No long-term safety data for chronic high-dose exposure

See also

• Selank · synthetic stabilized analog by C-terminal Pro-Gly-Pro extension
• Semax · related Russian-developed nootropic peptide

References

• Najjar VA, Nishioka K. Nature 1970. [PMID 5479452](https://pubmed.ncbi.nlm.nih.gov/5479452/)
• Siemion IZ, Kluczyk A. Peptides 1999. [PMID 10465517](https://pubmed.ncbi.nlm.nih.gov/10465517/)