Research Only Immune & Anti-Inflammatory

HD6

also known as: human α-defensin 6, DEFA6, defensin α6, enteric α-defensin 6

The Paneth cell α-defensin that does not kill directly — HD6 traps enteric pathogens by self-assembling into fibrillar "nanonets" (Chu et al., Science 2012), a mechanism unique among the defensin family. Poor microbicidal activity in vitro was a decade-long puzzle until the trapping mechanism was discovered.

A 32-amino-acid cationic α-defensin secreted by small-intestinal Paneth cells alongside HD5, sharing the disulfide-stabilised defensin fold but mechanistically distinct. Unlike other α-defensins, HD6 has weak direct microbicidal activity in standard liquid killing assays; its principal function, demonstrated by Chu, Arnold, Lu, Sankaran, Wehkamp, Stange, Bevins and colleagues (Science, 2012), is to self-assemble on contact with bacterial surface proteins into extracellular fibrillar "nanonets" that entangle invading enteric pathogens (notably Salmonella typhimurium) and prevent mucosal invasion.

Mechanism of action

Unique among α-defensins. Upon Paneth cell degranulation, mature HD6 is released into the crypt lumen where it binds to bacterial surface proteins (including Salmonella flagellin and fimbriae) and self-assembles into higher-order fibrillar nanonets that physically entangle bacteria and prevent mucosal adherence and invasion. Direct membrane-permeabilising microbicidal activity is weak compared to HD5 or HNP-1–3 (explaining early reports that HD6 "was not a real defensin"). Mouse knock-in experiments with human DEFA6 showed marked protection against Salmonella invasion that was abolished by mutations disrupting the nanonet-assembly interface — directly validating the trapping mechanism. Also contributes to shaping of ileal microbiota composition alongside HD5.

Primary uses

  • Research reagent for mucosal antimicrobial peptide studies
  • Inflammatory bowel disease research
  • Host-defense research on bacterial trapping and anti-invasion mechanisms
  • Template for rational design of anti-invasion mucosal therapeutics (early-stage, no clinical product)

Typical dosing

Not established

⚠ No human dosing established. HD6 has never been administered as a therapeutic.

Regulatory status

Not a drug. HD6 is an endogenous human Paneth cell defensin studied as a research reagent for mucosal immunity research. Like HD5, Paneth cell HD6 expression is reduced in ileal Crohn disease.

References

  1. [pubmed] Chu H, Pazgier M, Jung G, et al. "Human α-defensin 6 promotes mucosal innate immunity through self-assembled peptide nanonets." Science, 2012;337(6093):477-481.
  2. [pubmed] Jones DE, Bevins CL. "Defensin-6 mRNA in human Paneth cells: implications for antimicrobial peptides in host defense of the human bowel." FEBS Lett, 1993;315(2):187-192.
  3. [pubmed] Wehkamp J, Salzman NH, Porter E, et al. "Reduced Paneth cell alpha-defensins in ileal Crohn disease." Proc Natl Acad Sci USA, 2005;102(50):18129-18134.

Related peptides

HD5

The Paneth cell α-defensin — the dominant antimicrobial peptide of the human small intestine, stored at millimolar concentrations in Paneth cell secretory granules and released into the crypt lumen upon cholinergic or bacterial stimulus. Reduced HD5 expression is a recognised feature of ileal Crohn disease.

HNP-1

The prototype human α-defensin — isolated from neutrophil granules by Ganz, Selsted and Lehrer in 1985; the dominant antimicrobial peptide in human neutrophils and a workhorse molecule of innate immunity. Research peptide only: no defensin has ever been developed as an approved drug.

hBD-1

The constitutive epithelial β-defensin — first isolated from haemodialysate urine by Bensch, Schröder and colleagues (FEBS Letters 1995). Constitutively expressed (unlike hBD-2 and hBD-3, which are inducible), salt-sensitive in standard assays, and a major component of urogenital and airway surface antimicrobial defense.

hBD-2

The inducible β-defensin — cloned by Harder, Bartels, Christophers and Schröder (Nature 1997) from the lesional scales of psoriasis patients, with the paper framing psoriatic skin as a paradoxical "almost-never-infected" phenotype driven by massive β-defensin induction. Induced by TLR / NF-κB signalling in response to bacterial lipopolysaccharide and pro-inflammatory cytokines (IL-1, TNF-α).

hBD-3

The broad-spectrum β-defensin — active against Gram-positive, Gram-negative and fungal targets, and largely salt-insensitive (unlike hBD-1). Isolated independently in 2001 by Harder et al. and by García et al. from psoriatic skin and tonsil respectively. The β-defensin most studied for clinical translation because of its salt tolerance.
Disclaimer

This entry is for educational purposes only and does not constitute medical advice. Dosing information reflects published regulatory or research data and is not a recommendation. Many compounds described here are not approved for human use in the United States. Consult a licensed medical professional before considering any peptide therapy.