Immune & Antimicrobial Peptides: The Complete Reference

Immune peptides are short amino-acid sequences studied for their effects on immune function — thymic maturation of T cells, innate antimicrobial defense, inflammation modulation, and correction of immunodeficiency. The class spans four sub-categories with sharply different evidence bases. Thymic peptides (Thymosin Alpha-1, Thymopentin, Thymopoietin, Thymulin, Zinc Thymulin, Thymus Extract, Thymalin) carry decades of clinical evidence; Thymosin Alpha-1 is marketed as ZADAXIN and approved for hepatitis B and hepatitis C in more than 35 countries, and Thymopentin was sold as Timunox in Italy until 2003 for primary immunodeficiency, atopic eczema, and rheumatoid arthritis. Antimicrobial peptides (LL-37 and the cathelicidins, defensins, magainin, cecropin) are endogenous innate-immunity effectors, and they represent the most active peptide-drug development area of 2026, with candidates like pexiganan, omiganan, and iseganan in late-stage clinical programs. Bioregulator peptides (Vilon, Chonluten, KPV, Cortistatin) are the Khavinson family and adjacent small-peptide regulators positioned as immune modulators in Russian and Eastern-European clinical tradition; Western independent replication is limited. Specialized immune peptides (VIP, Aviptadil) include the FDA-EUA-considered COVID-19 ARDS agent RLF-100 (Aviptadil). The editorial frame across the hub: thymic peptides carry among the strongest clinical-trial evidence of any peptide category on PeptaHub; antimicrobial peptides are the most active peptide-drug development pipeline but have not yet produced a first-in-class US approval; bioregulators remain research-tier in the West. The hub below covers 17 compounds, ordered by evidence tier and immune subsystem.

Immune peptides work through four mechanisms that map to the pillar's four sub-classes. Thymic peptides (Thymosin Alpha-1, Thymopentin, Thymulin) restore T-cell maturation and function by mimicking thymic microenvironment signals — particularly relevant in post-chemotherapy, age-related thymic involution, and HIV contexts; Thymosin Alpha-1 is a TLR9 agonist that modulates regulatory T cells and dendritic-cell maturation. Cathelicidins and defensins disrupt bacterial membranes by electrostatic interaction with negatively-charged lipids, creating transmembrane pores and driving bacterial lysis; they also bridge innate and adaptive immunity by modulating dendritic-cell and T-cell activity. KPV and alpha-MSH-derived peptides downregulate NF-κB signaling and suppress pro-inflammatory cytokine production via the MC1R-MC5R system. VIP and its synthetic analog Aviptadil activate VPAC1/VPAC2 receptors on alveolar type II cells, reducing cytokine storm and preserving surfactant production in acute respiratory distress — the mechanistic basis for RLF-100's EUA consideration in COVID-19 ARDS.

Thymic peptides and T-cell restoration (Thymosin Alpha-1, Thymopentin, Thymulin, Thymopoietin, Zinc Thymulin, Thymus Extract, Thymalin)

The thymus gland matures naive T cells into functional immune effectors, but its function declines with age — a process called thymic involution that is a recognized hallmark of aging. Thymic peptides are short sequences either isolated from thymic tissue or engineered to mimic thymic microenvironment signals; they restore T-cell maturation in states where the thymus is involuted, injured, or chemotherapy-depleted. Thymosin Alpha-1 is a 28-amino-acid peptide that agonizes TLR9 on dendritic cells, modulates regulatory T cells bidirectionally, and accelerates dendritic-cell maturation; 374+ PubMed entries index its immune research. Thymopentin is the active 32-36 pentapeptide fragment of the 49-aa Thymopoietin parent protein, with 561 PubMed entries and a historical Italian approval (Timunox). Thymulin is a nonapeptide whose activity is strictly zinc-dependent — hence the cross-listed Zinc Thymulin entry — and restores T-cell function in zinc-deficient states. Thymalin is a Khavinson bioregulator with Russian clinical use.

Antimicrobial peptides — the innate-immunity arsenal and FDA-approved lipopeptides (LL-37, Cathelicidins, Defensins, Magainin, Cecropin, Gramicidin, Polymyxin B)

Antimicrobial peptides disrupt bacterial membranes by electrostatic attraction to negatively-charged lipids followed by pore formation via carpet-like or toroidal mechanisms. They kill by lysis, not by metabolic blockade, which gives them a fundamentally different resistance profile than conventional antibiotics. LL-37 is the primary human cathelicidin (2,976 PubMed entries); defensins (HNP1-4, HD5-6, hBD1-4) are produced by neutrophils and epithelial cells (2,411 PubMed entries); magainin is the frog-skin archetype that founded the antimicrobial-peptide drug-discovery field; and cecropin comes from insect hemolymph. Development candidates include pexiganan (a magainin analog that reached Phase 3 for diabetic foot ulcers), omiganan, and LTX-109. The two FDA-approved members of this class — gramicidin (topical ophthalmic, Neosporin co-formulation, cation-channel mechanism) and polymyxin B (cyclic lipopeptide, last-resort IV for MDR gram-negative infections, lipid-A-binding mechanism) — contrast with the developmental status of the endogenous-analog candidates: topical use is routine, systemic use is dose-limited by the same membrane-disruption mechanism that drives efficacy. Both are present in Neosporin Ophthalmic Solution alongside neomycin, illustrating the commercial path AMPs have actually taken (narrow-indication topicals) versus the broad systemic antibiotic role LL-37 analogs still chase. No first-in-class systemic AMP has achieved FDA approval as of 2026; the principal obstacle is hemolysis and cytotoxicity at systemically-effective antimicrobial doses.

Bioregulator and inflammation peptides (Vilon, Chonluten, KPV, Cortistatin)

Khavinson-family bioregulators are small peptides (dipeptides, tripeptides, tetrapeptides) from Vladimir Khavinson's St. Petersburg-based program, positioned as immune and systemic-aging regulators through a mechanism of direct gene-expression modulation. Vilon is the KE dipeptide; Chonluten (KED) targets lung and bronchial function. KPV is the α-MSH C-terminal tripeptide (lysine-proline-valine) that inhibits NF-κB signaling and suppresses pro-inflammatory cytokine production; it is cross-listed in the Recovery pillar for its inflammatory-bowel-disease and wound-healing research. Cortistatin is a natural somatostatin-family peptide that binds somatostatin receptors and also exhibits independent immunomodulatory activity. The bioregulator sub-class has substantial Russian and Eastern-European clinical evidence but limited independent Western replication.

Vasoactive immune peptides (VIP, Aviptadil)

Vasoactive intestinal peptide is a 28-amino-acid peptide that activates the VPAC1 and VPAC2 G-protein-coupled receptors. In the lung, VIP activates alveolar type II cells, suppresses cytokine-storm inflammatory signaling, and preserves surfactant production — the mechanistic rationale behind Aviptadil (RLF-100), the synthetic VIP formulation that received FDA EUA consideration for COVID-19 ARDS in 2020. Beyond respiratory indications, VIP and Aviptadil are investigational in sarcoidosis and pulmonary hypertension, with ongoing research into oral and inhaled dosing routes.

20 peptides, ordered by clinical evidence tier. Each entry links to the full profile with mechanism, dosing, side effects, and legal-status detail.

The Immune pillar spans a wider evidence range than any other PeptaHub hub — from Thymosin Alpha-1 with 35+ country approvals and 374 PubMed indexations to Khavinson bioregulators with minimal Western independent replication. The comparison table orders compounds by regulatory status first (approved, former-approval, EUA, research) and secondarily by immune subsystem.

Thymosin Alpha-1 is the most clinically-validated peptide on the Immune hub — 35+ country approvals and the strongest evidence base. Thymopentin has historical Italian approval and extensive human data but is no longer commercially marketed. Aviptadil's COVID-19 EUA is time-bounded and unlikely to extend to routine clinical use. The antimicrobial-peptide class is the most active peptide-drug development area in 2026 but has not yet yielded a first-in-class approval; pexiganan, omiganan, and LTX-109 are the candidates to watch. Bioregulators (Vilon, Chonluten, KPV) remain research-tier in the West despite substantial Russian clinical evidence.

Thymosin Alpha-1 has the strongest safety record in the category, with decades of marketed use and well-characterized adverse events (mild injection-site reactions, rare hypersensitivity); it is generally safe in immunocompromised hosts. Antimicrobial peptides carry mechanism-specific risks — hemolysis and cytotoxicity at systemically-effective doses — that explain why the field has struggled to achieve a first-in-class approval despite more than 30 years of development. Bioregulator peptides from Russian sources have limited Western pharmacovigilance; users should treat them as research-tier regardless of regional-approval status. The largest cross-category safety gap is supply-chain: most Immune peptides marketed to US consumers are sold as research chemicals by gray-market vendors, bypassing pharmaceutical sterility and potency controls. For Thymosin Alpha-1 specifically, the FDA has issued warning letters about compounded versions; the only regulated US pathway is clinical-trial enrollment or legal import of approved foreign-market product. See /methodology for PeptaHub's legal-status reasoning.

The Immune pillar is where foreign regulatory approval most strongly contradicts US unapproved status. Thymosin Alpha-1 has been used in Italy, China, and 33+ other countries for decades; the absence of US approval reflects the economics of running a US pivotal trial for an imported peptide, not the compound's safety or efficacy. Users seeking immune support with real evidence should understand that Thymosin Alpha-1 has peer-reviewed Phase 3 data in hepatitis and a place in WHO Essential Medicines candidate lists for sepsis adjuncts. Antimicrobial peptides are a promising-but-not-yet-clinical class; LL-37 analogs and defensin-derived compounds are in trials but will not be available for routine use until at least 2027–2029. Bioregulator peptides are the most speculative sub-class — their Russian clinical tradition is substantial but not independently replicated in the West. The rational approach: clinician-supervised Thymosin Alpha-1 (from pharmaceutical-grade foreign-market sources or clinical-trial enrollment) for users with genuine immune deficits; watchful waiting on antimicrobial peptides until first-in-class approval; skepticism of bioregulators until Western trials emerge.

How this class connects to the rest of PeptaHub's peptide coverage. Start with the full category index if you want to browse everything.

External citations underpinning this page. PeptaHub's full sourcing methodology is documented at /methodology — every claim on this page traces back to one of these references or a linked profile.

• Thymosin Alpha-1 immune literature (PubMed search, 374 results) — PubMed
• Thymopentin TP-5 research (PubMed search, 561 results) — PubMed
• LL-37 cathelicidin antimicrobial research (PubMed search, 2,976 results) — PubMed
• Defensins innate immunity research (PubMed search, 2,411 results) — PubMed
• FDA Human Drug Compounding — Warning Letters — FDA

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