Mice without the cathelicidin antimicrobial peptide gene developed dramatically worse intestinal infections, proving cathelicidin is a critical first-line defense in the colon.
Cathelicidin-deficient mice couldn't resist infections normal mice fought offOral infection doses that were handled by normal mice caused extensive colon damage and systemic bacterial spread in mice lacking cathelicidin — demonstrating this peptide is not optional for gut defense.
What the researchers found
Mice lacking the cathelicidin gene (Cnlp-/-) were dramatically more vulnerable to intestinal infection than normal mice. When infected with Citrobacter rodentium — a pathogen that mimics dangerous human E. coli strains — cathelicidin-deficient mice developed significantly greater colon colonization, epithelial cell damage, and systemic spread of infection. Normal mice were protected from infection doses that reliably infected the knockout mice.
The study also showed that cathelicidin (mCRAMP) expression in the gut is concentrated in the colon's surface epithelial cells, and that colon cell extracts from normal mice killed C. rodentium significantly better than extracts from cathelicidin-deficient mice.
Why it matters
This study provided some of the first direct evidence that cathelicidin — the same antimicrobial peptide family that includes human LL-37 — is a critical defender of your colon against bacterial infection. It established that without cathelicidin, the colon is essentially unprotected against adherent bacterial pathogens, the same class of bacteria responsible for serious human infections like enteropathogenic and enterohemorrhagic E. coli.
The numbers in context
Cnlp+/+ vs Cnlp-/- knockout mice · Citrobacter rodentium infection model · Significantly greater colonization in knockouts · Epithelial cell damage increased · Systemic dissemination in knockouts · mCRAMP concentrated in colon surface epithelium
How the study worked
Knockout mouse study comparing cathelicidin-deficient (Cnlp-/-) mice to normal (Cnlp+/+) mice. Researchers mapped mCRAMP expression in the intestinal tract, tested synthetic mCRAMP's antimicrobial activity against C. rodentium in vitro, compared antimicrobial activity of colon cell extracts from both mouse types, and challenged both groups with oral C. rodentium infection to measure colonization, tissue damage, and systemic spread.
Who was studied
Cnlp+/+ and Cnlp-/- knockout mice challenged with Citrobacter rodentium
What this study cannot tell us
Mouse study using a murine pathogen (C. rodentium) as a model for human E. coli infections — direct translation to humans requires caution. The study focused on one pathogen type. mCRAMP is the mouse equivalent of human LL-37 but the two peptides have structural differences. The relative contribution of cathelicidin versus other antimicrobial defenses was not fully quantified.
How to read the evidence
Rated moderate: well-designed knockout mouse study with clear controls and consistent results across multiple outcome measures. The use of genetic knockouts provides strong mechanistic evidence, though findings are in mice, not humans.
When this study was published
Published in 2005. This is a foundational study that established cathelicidin's role in intestinal defense. Its findings have been widely cited and confirmed by subsequent research on antimicrobial peptides in gut immunity.
The bigger picture
This 2005 study was foundational in establishing that antimicrobial peptides aren't just backup defenses — they're essential. The finding that cathelicidin-deficient mice can't control colon infections helped shift the field's understanding of innate immunity in the gut. It also laid groundwork for research into whether reduced LL-37 expression might contribute to inflammatory bowel disease and other gut conditions in humans.
Questions still open
- Do people with low LL-37 levels have increased susceptibility to intestinal infections from pathogenic E. coli?
- Could supplemental cathelicidin or LL-37 help protect against gut infections in immunocompromised patients?
- How does cathelicidin interact with other antimicrobial peptides like defensins in the colon's defense system?
Common questions
What is cathelicidin and why does your colon need it?
Is this the same as LL-37?
Read the original research
Cathelicidin mediates innate intestinal defense against colonization with epithelial adherent bacterial pathogens.
Journal of immunology (Baltimore, Md. : 1950), 174(8), 4901-7
Citation
Iimura, Mitsutoshi; Gallo, Richard L; Hase, Koji; Miyamoto, Yukiko; Eckmann, Lars; Kagnoff, Martin F. (2005). Cathelicidin mediates innate intestinal defense against colonization with epithelial adherent bacterial pathogens.. Journal of immunology (Baltimore, Md. : 1950), 174(8), 4901-7.