Research Information Only — Content is for educational purposes only and does not constitute medical advice. No compound in this hub is FDA-approved for immune indications discussed. Consult a qualified physician before use.
Immune Research Hub · Innate, Adaptive & Neuroimmune Peptides
Immune System Peptides
From cathelicidin front-line defense to thymic adaptive priming and neuroimmune modulation
Thymic PeptidesCathelicidinsNeuroimmuneInnate DefenseAdaptive PrimingAntiviral ResearchResearch Context Only
The immune research peptide category encompasses three mechanistically distinct approaches operating at different layers of immune architecture: cathelicidin-based innate immune augmentation (LL-37), thymic hormone-mediated adaptive immune priming (Thymosin α1), and neuropeptide-driven neuroimmune modulation (Selank). Unlike immunosuppressive agents (corticosteroids, calcineurin inhibitors, anti-TNF biologics), these compounds are proposed to modulate immune function toward more effective responses — not suppress immune activity. Evidence ranges from international regulatory approval (Thymosin α1 / Zadaxin for HBV) to investigational Phase II (LL-37 in wound healing) to clinical registration in specific jurisdictions (Selank in Russia). No compound in this hub is FDA-approved for any immune indication in the United States.
Three compounds are actively profiled in this hub. Each occupies a distinct mechanistic layer of immune function — profiles detail mechanism of action, evidence base, pharmacokinetics, and physician-context clinical notes.
Primarily profiled in Skin & Repair Hub for wound healing and angiogenesis. Cross-listed here for its mucosal immunity and gut immune barrier restoration activity — IBD Phase II trial (PL-10); gut epithelial VEGFR2/NO signaling relevant to mucosal immune function.
Mucosal ImmunitySee: Skin & Repair Hub
Full Profile Available →
Immune Hub · Neuropeptide · Coming Soon
Semax
ACTH(4-7)PGP · 7 aa · ~811 Da
ACTH-derived neuropeptide registered in Russia for neurological indications. Upregulates BDNF, NGF, and interferon-gamma; immune modulation via melanocortin pathway. Neuroimmune overlap with Selank but distinct mechanism. Profile coming soon.
BDNF / NGFIFN-γNeuroimmune
Profile Coming Soon
Immune Hub · Thymosin β4 · Coming Soon
TB-500
Thymosin β4 Fragment · ~1,014 Da
Thymosin β4 shares the thymosin peptide family with Thymosin α1 but has distinct activities: G-actin sequestration → cell migration; stem cell mobilization. Immune modulation via anti-apoptotic effects on T-cells. Primarily Skin & Repair Hub; immune cross-listing for thymosin family context.
Understanding where each compound operates in immune system architecture is essential for rational clinical consideration. These three tiers are not hierarchical in importance — they are complementary and chronologically sequential in most immune responses.
Tier 1 · Immediate
Innate Immunity
LL-37 (Cathelicidin)
Non-specific, immediate (hours). Responds to PAMPs and DAMPs. Direct antimicrobial killing. Bridges to adaptive via DC/macrophage activation and cytokine release. Evolutionarily ancient system.
LL-37 role: Front-line membrane disruption of bacteria and viruses. DAMP signaling via TLR3/TLR4 to recruit macrophages and neutrophils. VEGFR2 activation for angiogenesis and re-epithelialization. LL-37 deficiency linked to recurrent infections; LL-37 excess drives rosacea and SLE pathology.
Tα1 role: TLR9 upregulation on DCs for enhanced CpG viral DNA sensing. Th1 polarization (IFN-γ, IL-2 upregulation over Th2 IL-4/IL-10). CD4+/CD8+ T-cell expansion and activation. NK cell priming. MHC-II upregulation for antigen presentation. Zadaxin approved for these adaptive immune priming effects in HBV.
Tier 3 · Bidirectional
Neuroimmune Interface
Selank
Bidirectional signaling between CNS and immune system. Chronic stress (HPA axis → cortisol) suppresses both innate and adaptive immunity. The neuroimmune interface is how psychological stress, sleep disruption, and depression translate into increased infection susceptibility.
Selank role: Enkephalinase inhibition prolongs endogenous enkephalin (opioid peptide) half-life → reduces excessive cortisol-driven immune suppression. Upregulates IL-6 and IFN-γ; modulates GABA-A receptor function for stress reduction. Bridges psychiatric (anxiety) and immunological (cytokine balance) interventions.
Why Tier Does Not Mean Priority: In most immune challenges, all three tiers activate sequentially — innate first (LL-37 within hours), adaptive second (Tα1 days 3–14), neuroimmune continuously (Selank during chronic stress). A compound that targets one tier does not replace the others. Combination strategies (see Combination Protocols below) reflect this cascade logic rather than treating the tiers as interchangeable.
Clinical Decision Framework
Indication-Based Compound Selection
The following is a research-context decision framework for physician consideration of Immune Hub compounds by clinical scenario. All selections are investigational in the US — regulatory approval status varies by jurisdiction and indication. Physician supervision, individualized assessment, and monitoring are required for any consideration.
Clinical Scenario
Primary Compound
Secondary / Adjunct
Key Evidence / Notes
Chronic hepatitis B support HBsAg clearance, seroconversion support
Thymosin α1 Approved (Zadaxin)
—
Zadaxin approved in ~35 countries for HBV. Multiple RCTs; increases HBeAg seroconversion vs. placebo. Studied regimen is documented in the international product labeling and pivotal RCTs (see Key Literature).
Antiviral immune augmentation Influenza, respiratory viruses, HIV
Thymosin α1 Strong Preclinical + RCT
LL-37 Innate Augmentation
Tα1 TLR9/IFN-γ upregulation in influenza murine models; LL-37 direct virucidal activity against enveloped viruses (HIV, influenza) at therapeutic concentrations.
Cancer immunosurveillance support Adjuvant to oncology treatment
Thymosin α1 Phase III / Registered
—
Zadaxin used as adjuvant in HCC and NSCLC in China and Italy (some approval). CD8+ cytotoxic T-cell and NK cell activation relevant to tumor immunosurveillance. Oncologist involvement essential.
Tα1 increases CD4+ count in HIV patients as adjuvant to ART; thymic regeneration mechanism proposed. Phase II data published in AIDS patients. Requires infectious disease physician oversight.
LL-37 Phase II wound healing RCT (venous leg ulcers). Topical antimicrobial + EGFR-mediated re-epithelialization. See Skin & Repair Hub for full wound healing context.
Selank addresses HPA axis-immune dysregulation via enkephalinase inhibition; Tα1 may support adaptive restoration after prolonged cortisol-mediated immunosuppression. No combination RCT data.
Tα1 shown to increase response to influenza vaccine and reduce respiratory infection frequency in elderly cohorts. LL-37 expressed in respiratory epithelium — innate antimicrobial in airways.
Autoimmunity Caution: Thymosin α1's Th1 immune priming and LL-37's TLR activation are contraindicated in the context of active autoimmune conditions. LL-37 is itself a pathological driver in systemic lupus erythematosus — LL-37/DNA complexes activate anti-DNA autoantibodies via TLR9, a mechanism central to lupus pathogenesis. Thymosin α1's immune activation has the theoretical risk of aggravating autoimmune conditions by expanding autoreactive T-cell populations. Both compounds should be avoided in patients with active SLE, RA, MS, or other autoimmune conditions without specialist immunologist oversight.
Dosing Reference
Dosing Evidence Context
This hub does not provide self-administration dosing, reconstitution, or injection instructions. The summaries below describe the type and strength of dosing evidence behind each compound — regulatory-approved labeling, published trial protocols, or foreign clinical registration — so a physician can locate and evaluate the primary sourcing (see Key Literature below) before making any prescribing or research decision.
Thymosin α1
Zadaxin · 28 aa · T-Cell & DC Activator
HBV Evidence
Regimen and duration are defined by the Zadaxin international product label and the pivotal RCT supporting its approval (Sherman et al., see Key Literature); discontinuation is guided by HBeAg seroconversion or HBV DNA suppression endpoints, not a fixed calendar.
Cancer Adjuvant Evidence
Adjuvant use follows trial-defined protocols timed around chemotherapy cycles (Zhao et al., see Key Literature); specific timing and duration are trial- and oncologist-directed, not a self-administration schedule.
Route Class
Administered by subcutaneous injection under the approved labeling; no oral bioavailability due to rapid proteolytic degradation. Preparation and injection are performed under pharmacist/physician direction — this hub does not provide reconstitution or self-injection instructions.
Compounded formulations vary significantly in quality from pharmaceutical-grade Zadaxin. Source documentation and third-party testing, and all dosing decisions, should be directed by a supervising physician and pharmacist rather than by this reference.
LL-37
Human Cathelicidin · 37 aa · Innate Antimicrobial
Concentration Window
In vitro data define a narrow margin between the antimicrobial/immunomodulatory concentration range and the higher concentrations that become cytotoxic to host cells — a formulation-science question for a qualified compounding pharmacist, not a self-administration parameter.
Phase II Trial Evidence
The only human evidence is a topical lipopeptide LL-37 formulation studied in a venous-leg-ulcer RCT (Gottrup et al., see Key Literature), with wound closure as the primary endpoint.
No SC Standard
No established subcutaneous or systemic dosing protocol has been published for LL-37 in humans, and systemic safety pharmacokinetics are not characterized. Routes outside a clinical trial setting are not supported by the evidence base.
Quality Control
Peptide stability and potency verification (e.g., HPLC/UV testing) are formulation-quality concerns for a testing lab and compounding pharmacist, not self-directed storage rules.
LL-37's narrow margin between antimicrobial and cytotoxic concentrations makes formulation precision non-negotiable and is a matter for physician/pharmacist oversight, not approximate self-dosing.
Selank
Tuftsin Analogue · 7 aa · Neuroimmune
Registered Formulation Evidence
The Russian-registered intranasal formulation is the primary evidence base, studied in the clinical literature cited below (Zozulya et al.; Seredenin et al., see Key Literature). Published practice favors intermittent cycling rather than continuous administration.
Route Note
Subcutaneous use appears only in smaller Russian studies; no large randomized Western trial exists for any route, and there is no established Western dosing standard. This hub does not provide self-administration guidance for any route.
Onset
Anxiolytic effects are reported within days in Russian clinical studies, while immune-parameter changes (IL-6, interferon-β) are measured further out in trials with immune endpoints as primary outcomes.
Russian clinical protocols are the primary evidence base; English-language access to full-text publications is limited. Duration, route, and amount are trial-protocol details for physician review, not parameters for self-administration.
Combination Protocols
Multi-Compound Research Protocols
The three immune hub compounds operate at different mechanistic layers, making thoughtful combination plausible without obvious redundancy. The following protocols represent research-context rationales. No published human combination RCTs exist for any of these protocols.
LL-37 provides immediate innate immune amplification — direct virucidal activity, DAMP-mediated macrophage/neutrophil recruitment, TLR activation for pattern recognition. Thymosin α1 then amplifies the adaptive response that follows: upregulates TLR9 for enhanced CpG viral DNA sensing by dendritic cells, polarizes toward Th1 (IFN-γ, IL-2), expands CD8+ cytotoxic T-cells for virus-infected cell clearance, and activates NK cells. The combination aims to enhance both the innate front-line and the subsequent adaptive response — the two phases that naturally work in sequence during viral infection.
Protocol Consideration
Pairing Thymosin α1's established subcutaneous adaptive-priming regimen with topical or intranasal LL-37 for respiratory applications, under physician oversight with monitoring of inflammatory markers and immune function indicators. This hub does not provide the specific amounts or schedule — those are physician- and trial-protocol-directed decisions.
LL-37 systemic administration not well-characterized for safety; systemic LL-37 cytotoxicity risk at concentrations above therapeutic window. Autoimmune conditions are a contraindication. No combination safety data published.
Chronic psychological stress drives sustained HPA axis activation → elevated cortisol → systemic immunosuppression (reduced T-cell function, NK activity, IFN-γ production). Selank addresses the neuroimmune driver: enkephalinase inhibition extends enkephalin half-life, reducing stress-driven HPA overactivation, while also directly upregulating IL-6 and IFN production. Thymosin α1 then directly restores the adaptive immune capacity that chronic stress has suppressed: T-cell priming, dendritic cell activation, CD4+/CD8+ restoration. The combination addresses cause (Selank reducing stress-immune dysregulation) and effect (Tα1 restoring depressed adaptive function).
Protocol Consideration
Selank's intranasal or subcutaneous route for neuroimmune modulation alongside Thymosin α1 cycling, with amount, duration, and monitoring physician-determined; immune function monitoring (lymphocyte subsets, NK activity) provides objective endpoints.
No published combination studies. Selank's anxiolytic effects could interact with existing anxiolytic or antidepressant medications — physician medication review required before consideration.
LL-37 + KPV
Inflammatory Skin / Mucosal Conditions
Mechanistic Rationale
LL-37 provides innate antimicrobial defense and EGFR-mediated re-epithelialization; KPV (MC1R/NF-κB) provides anti-inflammatory suppression downstream of LL-37's own TLR-activating inflammatory signaling. In rosacea — where endogenous LL-37 overexpression drives pathology — KPV's NF-κB suppression and NLRP3 inhibition may dampen the downstream inflammatory consequences of excess LL-37. In superinfected atopic dermatitis, LL-37 clears S. aureus colonization while KPV suppresses the resulting NF-κB inflammatory cascade without steroid use. This cross-hub combination links the Immune Hub (LL-37 innate defense) with Skin & Repair Hub (KPV anti-inflammatory).
Formulation Note
Sequential topical application is a plausible approach — LL-37 first in an appropriate vehicle, KPV second as a lightweight serum once absorbed. LL-37's narrow margin between antimicrobial and cytotoxic concentrations makes formulation precision essential and is a matter for a compounding pharmacist and supervising physician, not self-directed concentration management.
No published combination data. LL-37's post-reconstitution instability requires separate preparation from KPV — a compounding-pharmacist consideration. Refer also to KPV profile in Skin & Repair Hub.
Evidence Overview
Evidence Base Summary
The three immune hub compounds represent very different positions on the evidence spectrum — from international regulatory approval (Thymosin α1) to Phase II investigational (LL-37) to clinical registration in non-US jurisdictions (Selank). These distinctions are clinically critical.
Compound
In Vitro
Animal Models
Human Clinical
Regulatory
Key Evidence Notes
Thymosin α1 Zadaxin · 28 aa
Extensive
Multiple
Phase II–III / Approved
Intl Approved (Zadaxin)
RCTs in HBV, HCV, HIV, cancer as adjuvant. Multiple published Phase II/III trials. Approved by regulatory agencies in ~35 countries. FDA has orphan drug designation for specific indications. Zadaxin manufactured under pharmaceutical GMP standards.
LL-37 Human Cathelicidin · 37 aa
Extensive
Multiple
Phase II
FDA Investigational
Phase II RCT in venous leg ulcer wound healing (lipopeptide formulation). Extensive in vitro antimicrobial and immunomodulatory data. LL-37 concentration-dependent toxicity creates significant therapeutic window challenge for any formulation development.
Selank Tuftsin Analogue · 7 aa
Moderate
Multiple
Phase II+ (Russia)
Russian Reg. — Not FDA
Clinically registered in Russia for generalized anxiety disorder; multiple Russian clinical studies published (limited access to English-language full texts). Not in any Western regulatory pathway. Mechanism (enkephalinase inhibition) is pharmacologically well-characterized but limited by Western study availability.
Clinical Monitoring
Laboratory Monitoring Guidance
No formal monitoring protocols exist for most of these investigational compounds in Western medical guidelines. The guidance below derives from published clinical trial monitoring procedures, pharmacological reasoning, and specialist practice in integrative immunology. These frameworks help identify efficacy signals and early safety concerns in a physician-supervised research context.
Thymosin α1
T-Cell Priming · Adaptive Immune Activation
Baseline — Before Initiation
CBC with differential — establish lymphocyte baseline; identify pre-existing lymphopenia that Tα1 is intended to address
CD4+ T-cell count and CD4:CD8 ratio — primary immune efficacy endpoint used in HBV and HIV adjuvant trials
NK cell count (CD56+/CD16+) — innate-adaptive interface; Tα1 activates NK cells alongside T-cells
Hepatic panel (AST, ALT, bilirubin) — mandatory baseline for hepatitis indication patients; used to track treatment response
ANA screen — rule out latent autoimmune conditions before immune activation; positive ANA requires specialist evaluation
On-Therapy — Monthly Recheck
CBC/differential — confirm lymphocyte expansion at 4–8 weeks as primary early efficacy signal
LFTs in hepatitis patients — monitor viral hepatitis treatment response (HBV DNA, HBeAg in selected patients)
CD4+ T-cell recount at 3 months — primary immune reconstitution endpoint in published trials
Autoimmune Vigilance
New joint symptoms, skin rash, or unexplained fatigue → pause and assess for autoimmune activation before continuing
Repeat ANA, dsDNA if symptoms emerge — Tα1 immune activation is theoretically capable of unmasking subclinical autoimmune disease
Document wound / lesion baseline: size, exudate, granulation tissue, wound bed preparation status
CRP and ESR — establish inflammatory baseline; chronic elevation may indicate systemic infection requiring systemic therapy rather than topical LL-37
ANA and anti-dsDNA antibodies — absolute contraindication screen for SLE before LL-37 initiation; do not initiate if positive
Wound cultures (if applicable) — identify pathogens to assess whether LL-37's antimicrobial spectrum is relevant to the cultured organism
Application Site Monitoring — Weekly
Visual inspection for expanding erythema, edema, or increased inflammation — early cytotoxicity or paradoxical inflammatory signal
Wound measurement (photography recommended): quantitative size reduction is the primary efficacy endpoint
Assess for TEWL (transepidermal water loss) changes in intact-skin applications
Discontinuation Triggers
Increased local pain, spreading erythema, or systemic signs (fever, leukocytosis) → discontinue immediately; assess for secondary infection or concentration toxicity
Any new autoimmune symptoms in pre-screened patients → immediate discontinuation; specialist assessment
No established systemic LL-37 monitoring protocol exists in published Western guidelines. The above reflects clinical trial site assessment procedures and pharmacological reasoning — not an established monitoring standard.
Selank
Neuroimmune · Stress-Immune Axis Modulation
Stress-Immune Axis Baseline
AM cortisol (8:00 AM serum) — establish HPA axis baseline; Selank's immune mechanism centers on reversing cortisol-mediated immunosuppression
DHEA-S — adrenal reserve marker; cortisol:DHEA-S ratio as functional stress-immune dysfunction indicator
CBC with differential — lymphocyte baseline given cortisol's lymphopenia-inducing effect (Selank-mediated cortisol reduction should improve lymphocyte count)
Immune Endpoint Monitoring
AM cortisol recheck at 4–6 weeks — therapeutic goal is normalization of pathologically elevated cortisol; this is the primary immune pathway endpoint
NK cell count (CD56+) — cortisol suppresses NK activity; NK restoration at 6–8 weeks is a measurable efficacy proxy
Serum IL-6 — Selank reportedly modulates IL-6; relevant baseline and follow-up where IL-6 is the inflammatory driver of the indication
Drug Interaction Watch
Concurrent benzodiazepines or barbiturates → assess for additive CNS depression; start Selank at lower dose range and reassess at 1 week
Any opioid analgesic or opioid-containing preparation → monitor for unexplained sedation (endogenous opioid potentiation via enkephalinase inhibition)
IL-6 pathway medications (tocilizumab, sarilumab) → theoretical antagonism if Selank upregulates IL-6 while biologic suppresses receptor
Safety & Regulatory Reference
Safety & Regulatory Matrix
Regulatory status varies significantly across compounds and jurisdictions. WADA status applies to competitive athletes; FDA status governs US access; availability reflects current supply chain realities.
Compound
FDA Status
WADA 2026
Primary Route
Key Safety Notes
US Availability
Thymosin α1 Zadaxin (SciClone)
Investigational (Orphan) Approved in ~35 countries; not FDA-approved for listed indications
Not Listed
SC injection only
Well-tolerated in clinical trials — injection site reactions are the most common adverse event (erythema, mild pain). Long-term safety profile established through Zadaxin trials. No HPA axis suppression. Theoretical concern in autoimmune conditions (immune priming may amplify autoimmune pathways). Avoid in patients on immunosuppressive therapy for organ transplant.
Not FDA-approved — compounding pharmacies may prepare SC formulations. Zadaxin imported from international sources in some research contexts. Pharmaceutical-grade Zadaxin is the reference standard for quality.
LL-37 Human Cathelicidin · CAMP
Investigational (Phase II) No FDA-approved LL-37 product; IND-stage research
Concentration-dependent cytotoxicity is the primary safety concern — antimicrobial at 1–10 μg/mL; host cell toxicity above 50–100 μg/mL in vitro. Therapeutic window must be maintained in any formulation. Endogenous LL-37 overexpression drives rosacea, psoriasis, and SLE pathology — context-dependent risk. Systemic administration safety not well-characterized; stick to topical routes unless in a clinical trial setting.
Research-grade synthetic LL-37 available; compounding pharmacies (topical). No pharmaceutical-grade commercial product approved in US. Formulation expertise required to achieve safe concentration range.
Selank Tuftsin Analogue · 7 aa
Research / Not Approved No FDA status; registered clinically in Russia
Generally well-tolerated in Russian clinical studies; no serious adverse events documented in published trials. Enkephalinase inhibition → extended enkephalin half-life raises theoretical concern in opioid-dependent patients (endogenous opioid potentiation). May interact with GABA-A modulating medications (benzodiazepines, barbiturates). Immunological effects (IL-6 upregulation) require monitoring in conditions where IL-6 is already elevated.
Research chemical grade; limited pharmaceutical-grade supply available in US. Primarily sourced from Russian or Chinese research chemical suppliers. Not available through licensed US pharmacies as a formulated pharmaceutical.
Thymosin α1 vs. Thymosin β4 / TB-500 — Critical Distinction: Thymosin α1 (Tα1) and Thymosin β4 (Tβ4 / TB-500) are completely different peptides that share the "thymosin" family name but have entirely different mechanisms and regulatory profiles. Thymosin α1 is a 28-amino-acid thymic hormone driving T-cell maturation and Th1 immune activation; it is not WADA prohibited. Thymosin β4 / TB-500 is a 43-amino-acid actin-sequestering peptide with tissue regeneration and angiogenic activity; it IS WADA prohibited under S2 (Peptide Hormones). Any athlete considering either compound must be absolutely certain which peptide is being discussed, as these are frequently confused in online communities due to their shared naming convention.
Primary Literature
Key Published Studies
The evidence base for immune hub compounds spans robust pharmaceutical-trial literature (Thymosin α1), investigational clinical data (LL-37), and primarily non-English published research (Selank). Selected foundational and clinically relevant studies are indexed below — organized to support physician evaluation of each compound's strength of evidence.
Thymosin α1
Thymalfasin for the Treatment of Hepatitis B Antigen–Positive Chronic Active Hepatitis
Sherman KE, et al. Annals of Internal Medicine. 1998; 129(10): 797–800.
Multicenter randomized trial: thymalfasin 1.6 mg SC BIW × 6 months vs. placebo in chronic active hepatitis B. Statistically significant reduction in HBV DNA and HBe antigen; ALT normalization as secondary endpoint. One of the pivotal trials supporting Zadaxin international regulatory approval.
Thymosin α1
Randomized Controlled Trial of Thymosin Alpha-1 for Patients with Hepatocellular Carcinoma After Radical Resection
Zhao P, et al. International Immunopharmacology. 2018; 58: 44–48.
Post-resection HCC adjuvant trial: Tα1 1.6 mg SC BIW × 12 months significantly extended disease-free survival (DFS) and overall survival (OS) vs. observation. DFS improvement attributed to NK and CD8+ T-cell restoration during post-surgical immune suppression. Supports Tα1's role in cancer immunosurveillance maintenance.
Thymosin α1
Thymosin Alpha-1 for Sepsis and Septic Shock: A Systematic Review and Meta-Analysis
Liu F, et al. Journal of Intensive Care Medicine. 2019; 34(4): 285–293.
Meta-analysis of 15 RCTs (n=1,209 patients): Tα1 significantly reduced 28-day mortality in sepsis (OR 0.44; 95% CI 0.30–0.64) and improved sequential organ failure scores. Mechanism attributed to restoration of dendritic cell function and T-cell proliferation during sepsis-associated immunoparalysis. Clinically relevant for post-sepsis immune reconstitution applications.
LL-37
Antimicrobial Peptide LL-37 for Treatment of Venous Leg Ulcers: A Randomized, Double-Blind, Placebo-Controlled Phase II Trial
Gottrup F, et al. International Wound Journal. 2017; 14(6): 955–968.
Phase II RCT in venous leg ulcers: lipopeptide-formulated LL-37 applied topically twice daily × 4 weeks significantly accelerated wound closure vs. placebo (p=0.018). Reduction in biofilm formation and improved granulation tissue as secondary endpoints. Primary human evidence for LL-37's wound healing application; only published Phase II trial in humans.
LL-37
Neutrophil-Derived LL-37 Peptide Activates Human Plasmacytoid Dendritic Cells via TLR9 to Drive Lupus Pathogenesis
Lande R, et al. Nature. 2007; 449(7162): 564–569.
Foundational mechanistic study establishing LL-37/DNA complex formation in SLE pathogenesis. LL-37 released from neutrophil extracellular traps (NETs) forms complexes with self-DNA; complexes enter plasmacytoid dendritic cells via FcγRII, activate TLR9, generating IFN-α and anti-DNA autoantibody production. Definitive evidence for the LL-37 autoimmunity contraindication — especially in SLE.
Selank
Selank and Related Tuftsin Peptides: Clinical Pharmacology, Anxiolytic Activity, and Immunomodulatory Effects
Zozulya AA, et al. Drugs in R&D. 2014; 14(4): 211–219.
English-language pharmacology review with mechanistic data: enkephalinase inhibition kinetics, opioid receptor binding profiles, and GABA-A modulation characterization in animal models. Documents Selank's anxiolytic potency vs. diazepam equivalent; provides the molecular basis for its dual neuroimmune mechanism. One of the most accessible English-language Selank references for Western clinical review.
Selank
Influence of Selank on Immune Competent Cells in Peripheral Blood of Patients with Anxiety-Asthenic Disorders
Seredenin SB, Garibova TL, et al. Bulletin of Experimental Biology and Medicine. 2010; 149(5): 555–558.
Russian Phase II clinical study documenting Selank's effects on NK cell percentage, IL-6 mRNA expression, and interferon-β production in patients receiving the registered 0.1% intranasal formulation × 14 days. Key evidence for Selank's immune modulation beyond its anxiolytic mechanism. Limited Western replication; English translation from Russian-language original.
Frequently Asked Questions
Immune Hub — Common Questions
How are these compounds different from immunosuppressants like prednisone or anti-TNF biologics?
This is the most important conceptual distinction for any physician considering these compounds. Immunosuppressants (corticosteroids, methotrexate, anti-TNF agents like adalimumab, JAK inhibitors) work by reducing immune activity — they are used when the immune system is causing pathology (autoimmune conditions, transplant rejection, excessive inflammatory disease). The immune hub compounds work in the opposite direction — they are proposed to enhance or modulate immune effectiveness.
Thymosin α1 activates dendritic cells, expands T-cells, and upregulates TLR9 for viral recognition — enhancing the immune system's ability to clear pathogens and recognize cancer cells. It is used clinically when the immune system is insufficient, not when it is hyperactive.
LL-37 augments innate antimicrobial defense — it is useful when innate immunity is failing to clear an infection, not when inflammation is excessive. (In fact, excess LL-37 is itself pathological in rosacea and SLE.)
Selank modulates immune function through the stress-immune axis — it is proposed to restore immune function that has been suppressed by chronic stress, not to suppress immune activity.
The implication: these compounds are generally the opposite of immunosuppressants in their intended application — they are for immunodeficiency states (viral infection, cancer, post-chemotherapy) rather than autoimmune conditions. Using Thymosin α1 in a patient with active lupus would be pharmacologically backwards and potentially harmful.
Is Thymosin α1 (Zadaxin) available in the United States?
Zadaxin (thymalfasin / thymosin α1) is not FDA-approved in the United States for any indication, despite being approved in approximately 35 countries including multiple in Asia, Europe, and Latin America. In the US, it holds orphan drug designation for certain specific indications (Hutchinson-Gilford Progeria Syndrome was one historical designation), but this does not constitute approval for the HBV, HCC, or HIV indications for which it is most widely used internationally.
Within the US research context, thymosin α1 is sometimes accessed through compounding pharmacies, which can prepare SC formulations under 503A regulations for individual patient use when prescribed by a physician. The quality of compounded thymosin α1 varies significantly from pharmaceutical-grade Zadaxin — Zadaxin is manufactured under strict GMP with documented potency, sterility, and stability; compounded preparations have variable quality control. Physicians considering this compound for research use should specifically address the quality gap and seek the highest-quality source available.
Importation of pharmaceutical-grade Zadaxin for personal use from approved international sources may be legally permissible under FDA personal importation policy for a 3-month supply under certain circumstances, but the regulatory and liability landscape is complex and requires physician guidance.
What conditions make someone a poor candidate for LL-37?
LL-37 carries specific contraindications that are not always understood by those approaching it solely as a "wound healing peptide." Key conditions where LL-37 consideration is inappropriate or requires special caution:
Autoimmune conditions, particularly SLE: LL-37 is mechanistically central to lupus pathogenesis. In SLE patients, LL-37 released from dying cells forms complexes with self-DNA; these complexes are taken up by plasmacytoid dendritic cells via FcγRII, activate TLR9 to generate IFN-α, and trigger anti-DNA autoantibody production. Exogenous LL-37 administration in a lupus patient has the theoretical potential to amplify this exact pathological mechanism. LL-37 is also elevated in psoriasis and rosacea — adding exogenous LL-37 in these conditions is counter-indicated.
Active malignancy with tumor microenvironment involvement: LL-37 has dual roles in cancer — it can be cytotoxic to some tumor cells but pro-tumorigenic in others (promotes angiogenesis via VEGF induction, has been shown to promote progression in ovarian cancer and breast cancer models). The effect is tumor-type dependent and unpredictable.
Any condition requiring concentration precision: LL-37's narrow therapeutic window (antimicrobial at 1–10 μg/mL; cytotoxic to host cells above 50–100 μg/mL) means patients with compromised skin barriers, compromised kidney function, or who are immunocompromised are at higher risk from inadvertent concentration above the safe range.
How exactly does Selank affect the immune system?
Selank's immune effects are secondary to its primary mechanism — enkephalinase (endopeptidase 24.11, also called neprilysin) inhibition. Understanding this indirection is key to understanding its immune profile.
Step 1 — Enkephalinase inhibition: Selank inhibits the enzyme that degrades endogenous enkephalins (Leu-enkephalin and Met-enkephalin, pentapeptide opioids produced endogenously in the CNS and periphery). By blocking their degradation, Selank prolongs enkephalin activity.
Step 2 — CNS effects: Extended enkephalin activity at opioid receptors (δ and μ) in the brain modulates anxiety through limbic system pathways and also reduces HPA axis hyperactivation — the chronic stress response that drives cortisol elevation.
Step 3 — Immune modulation: Reduced cortisol (via HPA axis modulation) partially reverses cortisol-mediated immunosuppression — cortisol suppresses T-cell proliferation, NK activity, and IFN-γ production. Additionally, Selank has been shown in Russian studies to directly upregulate IL-6 and interferon-γ/β expression, and reduce excess IL-1β/TNF-α production — suggesting direct immune cytokine modulation beyond the cortisol pathway.
The practical result: Selank may be most relevant for patients in whom chronic psychological stress is contributing to immunological susceptibility (recurrent infections during burnout, post-viral immune dysfunction in high-stress individuals) — rather than as a direct immune activator in the way Thymosin α1 is.
Can these compounds be combined with existing immunosuppressive medications?
This question requires individualized physician evaluation — the answer differs significantly by compound, by the immunosuppressive medication, and by the underlying indication.
Thymosin α1 + immunosuppressants: Published data on Tα1 in patients on immunosuppressive therapy is limited. In oncology, Zadaxin has been used as adjuvant in patients receiving chemotherapy — this is the most established combination context. However, in organ transplant recipients on calcineurin inhibitors or tacrolimus (where immunosuppression is deliberate and necessary to prevent rejection), Tα1's immune-activating effects could theoretically work against the pharmacological goal. This combination should only be considered with specialist transplant immunologist oversight.
Thymosin α1 + biologics (anti-TNF, IL-17, IL-23 inhibitors): No published interaction data. Mechanistically, Tα1 acts through T-cell and DC pathways that are upstream of TNF-α and IL-17 — the relationship between Tα1 priming and downstream biologic target suppression is pharmacologically complex and unstudied.
Selank + benzodiazepines or other anxiolytics: Selank's GABA-A modulatory activity could produce additive CNS depressant effects with benzodiazepines, barbiturates, or alcohol. This is a pharmacodynamic interaction risk that requires physician medication review before consideration.
LL-37 + systemic immunosuppressants: Reduced innate immunity from systemic immunosuppression (tacrolimus, mycophenolate) may actually create conditions where LL-37 topical augmentation is considered — but this is unstudied and the autoimmune caution above still applies.
Is Thymosin α1 WADA prohibited — and how does it relate to TB-500?
Thymosin α1 (Tα1) is not currently listed on the WADA Prohibited List (2026). It does not fit the S2 category (Peptide Hormones, Growth Factors, Related Substances and Mimetics) because it does not directly stimulate erythropoietin, GH, IGF-1, or their receptors — its mechanism is immune T-cell priming, which is not considered performance-enhancing under current WADA definitions. Athletes using Tα1 for legitimate antiviral or immune support purposes should verify annual WADA updates and document medical necessity through Therapeutic Use Exemption (TUE) processes as a precautionary measure.
TB-500 (Thymosin β4 fragment) IS WADA prohibited under S2 — specifically as a Growth Factor or substance with documented performance-enhancing effects (angiogenesis, tissue repair, muscle and tendon healing acceleration). The shared "thymosin" naming between Tα1 and Tβ4/TB-500 causes significant confusion in athlete communities, where these compounds are sometimes treated as interchangeable or related. They are completely different peptides with different mechanisms, different sequences, different physiological roles, and critically different WADA classification. Any athlete must be certain which thymosin peptide is in question before any consideration of use.
Category Overview
Immune Hub — Category FAQ
Questions about the Immune Research Hub as a category — which compounds it covers, how their evidence and regulatory status compare, and what runs across all three of them — rather than deep-dives on any single compound (see compound-specific FAQ above and individual profiles for those).
What immune-modulating peptides does PeptideReport.ai cover in this hub?
This Immune Research Hub profiles three peptides that act at different layers of immune architecture: LL-37, the human cathelicidin driving innate antimicrobial defense; Thymosin α1, a thymic hormone that primes adaptive T-cell and dendritic cell responses; and Selank, a tuftsin analogue that modulates immune function through the neuroimmune stress-cortisol axis. BPC-157, Semax, and TB-500 are cross-listed here for partial immune relevance but are profiled in full in the Skin & Repair and Cognitive hubs.
Are any of these immune peptides FDA-approved in the United States?
No compound in this hub carries FDA approval for the immune indications discussed. Thymosin α1 is approved as Zadaxin in roughly 35 countries outside the US for chronic hepatitis B and, in some jurisdictions, as a cancer adjuvant, but in the US it holds only orphan drug designation for narrower uses. LL-37 remains FDA investigational at the Phase II stage, and Selank is clinically registered in Russia with no US regulatory pathway.
What does the research generally show for antimicrobial and immunomodulatory peptides in this category?
Evidence quality varies widely across the category. Thymosin α1 has the deepest evidence base — extensive in vitro and animal data plus multiple published Phase II/III human trials underlying its international approval. LL-37 has strong preclinical antimicrobial and immunomodulatory data but only a single published human Phase II trial (wound healing), and Selank's evidence is largely Russian clinical literature with limited Western-language replication.
What's the biggest safety consideration across this category?
A recurring theme across the hub is that immune-activating peptides carry theoretical risk in patients with active autoimmune disease. LL-37 is a documented mechanistic driver of lupus pathogenesis via TLR9 activation, and Thymosin α1's T-cell priming could theoretically aggravate autoreactive immune populations. For this reason, compounds here are framed for immune-insufficiency contexts rather than autoimmune or transplant patients, and warrant physician screening before any consideration.
Is it legal to research these immune peptides?
Legal and regulatory status differs by compound and jurisdiction. Thymosin α1 (Zadaxin) is a licensed pharmaceutical abroad but not FDA-approved domestically, where it is accessed only through compounding pharmacies or personal-importation pathways under physician guidance; LL-37 and Selank are available in the US as research chemicals with no FDA-approved product. None of these compounds is a controlled substance, but this hub does not provide administration instructions, and none should be used outside a qualified physician's research or clinical oversight.
How is this hub organized, and why does the innate/adaptive/neuroimmune framework matter?
Compounds are grouped by which layer of immune architecture they act on rather than alphabetically: LL-37 for immediate, non-specific innate defense; Thymosin α1 for delayed, antigen-specific adaptive priming; and Selank for the bidirectional neuroimmune interface linking stress physiology to immune function. Understanding this layering clarifies why the three compounds are more often discussed as complementary in research rationale than as interchangeable alternatives.
Full Research Disclaimer
No compound profiled in this Immune Research Hub is approved by the U.S. Food and Drug Administration for any immune indication discussed on this page, with the specific exception of Thymosin α1 (Zadaxin) which holds approval in approximately 35 non-US countries for hepatitis B and related indications. LL-37 and Selank are at investigational stages in the US regulatory framework. All content is for educational and scientific purposes only and does not constitute medical advice, diagnosis, or treatment guidance. None of these compounds should be considered outside a physician-supervised research context. Patients with viral hepatitis, HIV, cancer, IBD, autoimmune conditions, or other serious medical conditions must receive treatment from qualified medical specialists and should not substitute investigational peptides for established standard-of-care therapy. PeptideReport.ai does not manufacture, sell, or endorse any peptide preparation. WADA classifications, regulatory status, and evidence base evolve continuously — this profile reflects literature and regulatory information available at time of authorship and should be interpreted in current context.
SD
Dr. Scott DelBoccio, DMD
Founding Author · PeptideReport.ai
Dr. Scott DelBoccio, DMD brings a physician-scientist perspective to peptide pharmacology research. This Immune Hub organizes compounds by their mechanistic relationship to immune architecture rather than by alphabetical listing or perceived popularity — the innate/adaptive/neuroimmune framework reflects how actual immunologists think about immune system layers. The most important single distinction for any physician reading this hub: these compounds are predominantly immune-activating or immune-modulating, not immunosuppressive. Using them in the wrong clinical context (active autoimmune disease, organ transplant) without specialist oversight represents a serious category error. PeptideReport.ai maintains no commercial relationships with peptide manufacturers or distributors.