Category
Immune Support
Peptides that modulate immune function through thymic signaling, toll-like receptor pathways, and cytokine regulation. Thymosin alpha-1 is the most clinically developed compound in this class, with approved use in multiple countries for viral hepatitis and as a vaccine adjuvant.
13 peptides in this category
What is thymosin alpha-1 and how does it support immunity?
Thymosin alpha-1 is a 28-amino-acid peptide derived from thymosin fraction 5, the thymic secretion that governs T-cell development. It works by activating toll-like receptor 9 on dendritic cells, enhancing Th1 cytokine responses, and improving T-cell and NK cell activity. It is approved in over 35 countries for hepatitis B and C treatment, and has been studied as an immune adjuvant in cancer therapy, vaccine protocols, and, more recently, in managing viral infection sequelae.
The immune system's peptide-based regulation is ancient and complex. Thymic peptides play a particularly well-studied role: the thymus produces several proteins that govern T-cell maturation, and synthetic analogs have been developed to replicate this signaling in conditions where thymic function is compromised. Thymosin alpha-1 (Ta1), a 28-amino-acid peptide originally isolated from thymosin fraction 5, is the most clinically developed. It is approved in over 35 countries for chronic hepatitis B and C, and has been studied as an adjuvant in cancer immunotherapy, COVID-19, and vaccine protocols. Its mechanism involves TLR-9 activation on dendritic cells and direct enhancement of Th1 cytokine production.
KPV, a tripeptide derived from the C-terminus of alpha-MSH (Lys-Pro-Val), has anti-inflammatory and antimicrobial properties through MC1R binding on immune cells and intestinal epithelium. It has been studied in models of inflammatory bowel disease and Candida infection. LL-37, the only known human cathelicidin, sits at the intersection of antimicrobial and immunomodulatory functions — it kills bacteria directly while also signaling immune cell recruitment and dampening excessive inflammatory responses. These peptides collectively represent how the immune system uses short sequences to coordinate complex, context-dependent responses.
Compounds
Peptides in this category
Defensin Alpha
PreclinicalHuman Neutrophil Peptides (HNP-1, HNP-2, HNP-3) · α-defensins
Alpha-defensins are cationic antimicrobial peptides secreted by neutrophils (HNP-1 to 4) and Paneth cells (HD-5, HD-6) in the small intestine. They kill bacteria, fungi, and enveloped viruses through membrane disruption and also function as chemokines, recruiting immune cells and bridging innate and adaptive immunity. Paneth cell alpha-defensins (HD-5, HD-6) play a critical role in shaping intestinal microbiome composition.
Elafin
Phase IITrappin-2 · SKALP
Elafin is an endogenous serine protease inhibitor (serpin-like) peptide produced by epithelial cells at mucosal surfaces. It inhibits neutrophil elastase and proteinase 3, protecting tissues from excessive inflammatory damage, while also exhibiting direct antimicrobial activity against bacteria and fungi. Research focuses on inflammatory bowel disease, cystic fibrosis, ARDS, and vaginal microbiome modulation, where recombinant elafin is in Phase 2 trials.
Enkephalins
PreclinicalLeu-Enkephalin · Met-Enkephalin
Enkephalins are endogenous opioid pentapeptides (Met-enkephalin and Leu-enkephalin) acting as natural ligands for delta and mu opioid receptors. They modulate pain, mood, reward, and immune function. Low-dose naltrexone (LDN) works partly by transiently blocking opioid receptors to upregulate enkephalin production. Methionine enkephalin (met-enkephalin) has shown immune-modulating and anti-tumor properties in research, particularly for HIV and cancer.
KPV
PreclinicalLys-Pro-Val · α-MSH C-terminal tripeptide
KPV is a tripeptide derived from the C-terminal sequence of alpha-melanocyte-stimulating hormone (α-MSH). It exhibits potent anti-inflammatory effects by inhibiting NF-κB signaling and proinflammatory cytokine production. Research is particularly focused on its potential for inflammatory bowel disease, colitis, and skin inflammation, with studies showing efficacy even when administered orally or topically.
LL-37
Phase ICathelicidin · hCAP18/LL-37
LL-37 is the only known human cathelicidin antimicrobial peptide, derived from the C-terminus of hCAP18 protein. It exhibits broad-spectrum antimicrobial activity against bacteria, fungi, and viruses by disrupting microbial membranes. Beyond direct killing, LL-37 modulates inflammation, promotes wound healing, and may have anticancer properties. Research focuses on chronic wound care, infection, and skin disorders like rosacea.
Selank
ApprovedSelanc · TP-7
Selank is a synthetic heptapeptide analog of tuftsin developed by the Russian Institute of Molecular Genetics. Approved in Russia for anxiety and cognitive disorders, it exhibits anxiolytic effects comparable to benzodiazepines without sedation or dependence. Research shows it modulates GABA, serotonin, and dopamine systems, enhances BDNF expression, and improves memory consolidation and learning.
C₃₃H₅₇N₁₁O₉ · 751.87 Da
Thymalin
ApprovedThymus Humoral Factor-Gamma 2 · THF-γ2
Thymalin is a peptide complex isolated from bovine thymus gland, approved in Russia for use as an immunomodulator. Research demonstrates it restores age-related decline in T-cell function, enhances bone marrow activity, and supports immune homeostasis. Long-term studies in elderly populations show reductions in all-cause mortality and improved immune resilience, positioning it as a key anti-aging immunotherapy research compound.
Thymopentin
ApprovedTP-5 · Timunox
Thymopentin (TP-5) is a synthetic pentapeptide corresponding to positions 32–36 of thymopoietin. It is approved in several countries for HIV infection, rheumatoid arthritis, and immune deficiencies. Research shows it selectively promotes T-cell maturation and differentiation, enhancing both cellular and humoral immune responses without causing immunosuppression.
Thymosin Alpha-1
ApprovedThymalfasin · Tα1
Thymosin Alpha-1 is a naturally occurring 28-amino-acid peptide derived from thymosin fraction 5 of the thymus gland. Approved in over 35 countries for hepatitis B, hepatitis C, and as an immune adjuvant in cancer therapy, it enhances T-cell maturation, dendritic cell function, and NK cell activity. Research continues to expand into sepsis, COVID-19, autoimmune conditions, and vaccine response enhancement.
C₁₂₉H₂₁₅N₃₃O₅₅ · 3108.29 Da
Thymosin Beta-4
Phase IITβ4 · LKKTETQ
Thymosin Beta-4 is the full-length 43-amino-acid peptide and one of the most abundant intracellular proteins in mammalian cells. It sequesters G-actin, regulating actin polymerization and cell motility, which underpins its role in wound healing, cardiac repair, and immune cell migration. Clinical trials have examined it for dry eye disease, epidermolysis bullosa, and cardiac repair after myocardial infarction.
Thymulin
PreclinicalSerum Thymic Factor · Facteur Thymique Sérique
Thymulin is a nonapeptide produced exclusively by thymic epithelial cells, requiring zinc for biological activity. It promotes T-cell differentiation, enhances cytokine production, and is a key marker of thymic function. Circulating thymulin levels decline with age, paralleling thymic involution. Research examines its role in autoimmunity, inflammatory diseases, and as a zinc-dependent immune regulator in aging.
Vilon
PreclinicalLys-Glu · KE dipeptide
Vilon is a synthetic dipeptide (Lys-Glu) developed at the St. Petersburg Institute of Bioregulation and Gerontology as a vascular cytoprotective peptide. Research demonstrates it reduces vascular endothelial cell aging, suppresses excessive collagen synthesis, and modulates the renin-angiotensin system. Long-term animal studies show improved vascular function and survival; it is often studied as part of peptide longevity protocols.
VIP
Phase IIVasoactive Intestinal Peptide · Vasoactive Intestinal Polypeptide
VIP (Vasoactive Intestinal Peptide) is a 28-amino-acid neuropeptide with pleiotropic anti-inflammatory, bronchodilatory, and immunomodulatory effects mediated through VPAC1 and VPAC2 receptors. Research spans pulmonary arterial hypertension (inhaled VIP trials), inflammatory bowel disease, sepsis, Parkinson's disease, and CIRS (chronic inflammatory response syndrome). It suppresses Th1 cytokines and promotes Treg cell function.
Research applications
What researchers are studying
T-cell maturation and adaptive immunity
Thymosin alpha-1 promotes differentiation of naive T-cells and enhances NK cell activity. In immunocompromised patients, it has been studied as a means of restoring functional immune responses without the toxicity of broader immunostimulants. Post-COVID studies have examined it for persistent immune dysregulation in long-COVID presentations.
Intestinal immune regulation
KPV has been studied specifically in gut models, where it appears to reduce NF-kB activation in intestinal epithelial cells and reduce secretion of pro-inflammatory cytokines including IL-8 and TNF-alpha. Oral and rectal formulations have been tested in animal models of colitis, positioning KPV as a candidate for gut-targeted immune modulation.
Innate immune defense
LL-37 is produced by neutrophils, macrophages, and epithelial cells in response to infection. Beyond its direct antimicrobial function, it acts as a chemoattractant for monocytes and T-cells, enhances toll-like receptor expression, and modulates the inflammatory response to avoid septic-spectrum overactivation. Its deficiency has been linked to increased susceptibility to skin, lung, and gut infections.
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