Human defensins

HNP-1 to HNP-4 (human neutrophil peptides, α-defensins); HD-5, HD-6 (enteric α-defensins); HBD-1 to HBD-4 (human β-defensins; HBD-2 = DEFB4); defensins

Antimicrobial & antiviral

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Summary

Class: Family of small (~29–45 amino acid) cationic host-defence peptides, folded by three internal disulfide bonds; naturally occurring in humans
Mechanism: Cationic peptides that disrupt microbial membranes (partly via binding the cell-wall precursor lipid II) and also signal to the immune system, recruiting and activating immune cells
Routes studied: Endogenous (made by neutrophils, Paneth cells, skin and mucosal epithelium). No approved exogenous defensin product; experimental delivery is topical/local in animals
Half-life: Not characterised as a drug; as endogenous peptides they act locally and are cleared quickly
Storage: Not applicable (not a supplied product)
Regulatory status: Not a medicine anywhere; a field of research, not a compound you obtain

Doses are as reported in studies or by the community — never recommendations.

1What it is

Defensins are among the body's oldest built-in antibiotics. They are small peptides, folded tightly by three internal disulfide bridges, that humans make in two main families: α-defensins (including the human neutrophil peptides HNP-1 to HNP-4, stored in neutrophils, and HD-5/HD-6 made by Paneth cells in the small intestine) and β-defensins (including HBD-1, which is made all the time, and HBD-2/HBD-3, which switch on in response to infection or inflammation in skin and mucosa).

They are not a research peptide that anyone injects. They are part of normal human immunity, and they appear on this site because people searching for antimicrobial peptides or "LL-37" (see LL-37) encounter them constantly and ask what they are. There is no community self-administration of defensins; the interest is scientific.

2How it's thought to work

Membrane disruption. defensins are positively charged and attracted to the negatively charged surfaces of bacteria. They insert into the microbial membrane and make it leaky. Several (notably HNP-1 and HBD-3) also bind lipid II, the building block bacteria use to make their cell wall, which blocks wall synthesis as well.

Broad targets. activity is reported against Gram-positive and Gram-negative bacteria, fungi and some enveloped viruses, though potency drops in the salt and protein conditions of body fluids.

Immune signalling. β-defensins act as chemoattractants, pulling immature dendritic cells and T cells to sites of infection via the CCR6 receptor, linking fast innate defence to the slower adaptive immune response.

Regulation. HBD-2 production is induced by bacterial products and by inflammatory signals; low intestinal HBD-2 has been linked to Crohn's disease of the colon.

Positively charged peptides drawn to the negatively charged bacterial surface, where they insert and open pores. No receptor is involved, which is why resistance develops slowly.Schematic — not to scale

3What the research shows

Not gradedestablished biology (not a grade for a therapy)

Role in human immunity

The existence and function of defensins in neutrophils, gut and skin is well documented in humans (Ganz 2003, Nat Rev Immunol). This is settled cell biology, not an intervention trial. [1]

Graded B/C

Gut defensins and inflammatory bowel disease

Reduced Paneth-cell α-defensins (HD-5/HD-6) have been associated with ileal Crohn's disease, and a low DEFB4 (HBD-2) gene copy number on chromosome 8 has been associated with colonic Crohn's disease (Wehkamp 2005, Gut; Fellermann 2006, Am J Hum Genet). These are association studies, not proof that giving defensins helps. [2][3]

Graded C/D

Defensins as antibiotic leads

Natural and engineered defensins and defensin-mimetics have been tested against resistant bacteria and in animal infection and wound models (numerous groups). Progress to human therapeutics has been limited by cost of synthesis, loss of activity in physiological salt, and potential toxicity to host cells at higher concentrations.

Graded C/D

Antiviral and antifungal roles

Laboratory evidence that α- and β-defensins can block entry or replication of certain viruses and inhibit fungi; clinical relevance as a treatment is unproven.

4Reported side effects and interactions

Literature-reported

As endogenous molecules there is no "side-effect" profile in the drug sense. Engineered defensins in preclinical work can be cytotoxic or pro-inflammatory to host cells at higher concentrations, which is one reason none has reached routine clinical use.

Community-reported

Community use: essentially none documented. Defensins are not self-administered.

Theoretical. Systemic cationic peptides carry general concerns about host-cell toxicity and immune activation; unquantified for defensins specifically in humans.

Interactions. Activity is reduced by physiological salt concentrations and by serum proteins — a pharmacological obstacle rather than a drug interaction.

Markers researchers commonly monitor

Defensins are themselves measured as markers in research rather than being compounds whose effects you track. Relevant measurements in the literature: No compound-specific safety markers apply because there is no compound being administered.

Marker	Why it's watched
Faecal/mucosal HBD-2 and HD-5	studied as markers of gut innate immunity in inflammatory bowel disease.
Plasma/neutrophil HNP-1–3	rise with neutrophil activation and sepsis; a research inflammation readout.
DEFB4 gene copy number	a fixed genetic marker studied in relation to Crohn's and psoriasis.

Free for everyone. Safety information is never behind a paywall.

5Formulation and handling

Not applicable — defensins are not supplied as a product for administration. Research-grade synthetic peptide is handled per laboratory protocol, not for use.

6Commonly studied alongside

LL-37 (the other major human host-defence peptide family), Nisin and other lipid II-binding antimicrobials, lysozyme.

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	Not a medicine; endogenous human peptides, no approved defensin product
European Union	Not authorised as a medicine
United Kingdom	Not a medicine
Australia	Not an approved product
South Africa	Not registered
Sport	Not listed by WADA (endogenous immune peptides; not a performance substance)

8Open questions

Can a defensin or defensin-mimetic be engineered to keep activity in body-fluid salt while sparing host cells?
Is low gut defensin a cause of, or a consequence of, inflammatory bowel disease?
Do defensins have a practical role as anti-infectives, or is their main value as immune signalling molecules?

9References

1Ganz T (2003). Defensins: antimicrobial peptides of innate immunity. Nat Rev Immunol. PubMed · DOI
2Wehkamp J et al. (2005). Reduced Paneth cell α-defensins in ileal Crohn's disease. Proc Natl Acad Sci / Gut. PubMed · DOI
3Fellermann K et al. (2006). A chromosome 8 gene-cluster polymorphism with low human beta-defensin 2 gene copy number predisposes to Crohn disease of the colon. Am J Hum Genet. PubMed · DOI
4Lehrer RI, Lu W (2012). α-Defensins in human innate immunity. Immunol Rev. PubMed · DOI
5Schneider JJ et al. (2005). Human defensins. J Mol Med. PubMed · DOI

10Community

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Self-reported side effects Phase 2

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11Page history

30 Oct 2026Profile published — awaiting medical review

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