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Architecture

Paneth cells and α-defensins (HD5, HD6)

Hypothesis Mechanism review
mechanism marker barrier inflammation microbiome
Editor's note
Paneth cell dysfunction—particularly loss of antimicrobial peptides HD5 and HD6—appears to be a specific, testable mechanism underlying ileal Crohn's disease rather than merely a secondary effect. This reframes CD pathogenesis from primarily immune dysregulation toward barrier-level microbial control, positioning it alongside emerging evidence that genetic variants in NOD2 and autophagy genes converge on this single cell type. Gastroenterologists managing refractory ileocecal disease and inflammatory bowel disease researchers should prioritize mechanistic investigation here, as Paneth cell restoration might offer a druggable entry point.

The small intestine has its own specialized defense system: Paneth cells at the bottom of the crypts of Lieberkühn, which produce potent antimicrobial peptides — particularly HD5 and HD6.

Paneth cells produce broad-spectrum antimicrobial peptides, most abundantly α-defensins HD-5 and HD-6. In small intestinal Crohn's disease, both these PC products are specifically reduced. Functional consequence: ileal extracts from Crohn's patients are compromised in bacterial clearance, and entero-adherent E. coli colonize the mucosa.

Mechanisms for defective Paneth cell function include: NOD2 (CARD15) loss-of-function mutations; disturbance of the Wnt pathway transcription factor TCF7L2 (TCF4); autophagy factor ATG16L1; ER stress protein XBP1; TLR9 and KCNN4.

Clinical implication: If the problem region is the ileocecal area, Paneth cell function is especially relevant. NOD2/CARD15 genotyping is standard in CD genetic panels. Defective α-defensin production can be tested via biopsy-based assays (research context).

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Published 2026-05-24 · Last kit-update 2026-05-24