Not All Cathelicidins Are Created Equal: How Antimicrobial Peptides Differ Across Species | Research

The takeaway

A head-to-head comparison of 12 cathelicidins from 6 species shows these antimicrobial peptides vary widely in their ability to kill bacteria, neutralize toxins, and regulate the immune system — meaning findings from LL-37 studies can't be assumed to apply to other cathelicidins.

12 peptides, 6 species
The largest standardized cathelicidin comparison to date showed functions vary dramatically — results from LL-37 studies cannot be generalized to other species

What the researchers found

Comparing 12 cathelicidins from 6 different species under identical lab conditions revealed that these antimicrobial peptides differ significantly in their functions — both between species and within the same species. Most cathelicidins killed E. coli and/or MRSA effectively, but a surprising finding emerged: under more realistic physiological conditions, antimicrobial activity against E. coli dropped for nearly all cathelicidins while activity against MRSA actually increased.

Seven of 12 cathelicidins could neutralize bacterial LPS (a toxin from gram-negative bacteria), and 7 could neutralize LTA (from gram-positive bacteria), but there was no correlation between the two abilities. Only 4 of 12 enhanced DNA-induced TLR9 activation, showing that immune-modulating functions are not universal across cathelicidins.

Why it matters

Most antimicrobial peptide research focuses on just two cathelicidins — human LL-37 and mouse CRAMP — and assumes findings apply broadly. This study shows that's a dangerous assumption: cathelicidins vary widely in what they can do. This matters for drug development because it means researchers can't simply pick any cathelicidin and expect the same results, and it opens the door to choosing specific cathelicidins for specific therapeutic applications.

The numbers in context

12 cathelicidins · 6 species · 7/12 neutralized LPS · 7/12 neutralized LTA · 4/12 enhanced TLR9 activation · tested against E. coli and MRSA

How the study worked

Researchers tested 12 cathelicidin peptides from 6 animal species under standardized conditions to enable direct comparison. They measured antimicrobial activity against E. coli and MRSA, tested the ability to neutralize bacterial toxins (LPS and LTA), assessed TLR modulation, chemokine induction, and phagocytosis regulation. Tests were conducted both in standard lab conditions and under more physiologically relevant conditions.

Who was studied

In vitro comparison of 12 cathelicidin peptides from 6 species

What this study cannot tell us

This is an in-vitro study using cell cultures and bacterial assays. How these functional differences translate to real infections in living animals or humans is unknown. The study tested antimicrobial activity against only two bacterial species. The physiological conditions used, while more realistic than standard lab conditions, still don't fully replicate the complexity of a living immune system.

How to read the evidence

This is a moderate-evidence in-vitro study with a well-designed comparative framework. The standardized conditions and breadth of peptides tested add rigor, but findings remain limited to laboratory settings.

When this study was published

Published in 2017, this study remains a key reference for cathelicidin functional diversity. Its warning against generalizing from LL-37 studies continues to influence how researchers design antimicrobial peptide experiments.

The bigger picture

Antimicrobial peptides are being explored as alternatives to conventional antibiotics, especially against drug-resistant bacteria like MRSA. Understanding which cathelicidins do what — and that they aren't interchangeable — is critical for selecting the right peptide candidates for drug development. This study also provides a practical framework for standardized comparison that the field has been lacking.

Questions still open

Which specific cathelicidins are the best candidates for anti-MRSA drug development given the enhanced activity under physiological conditions?
Why does physiological salt concentration reduce activity against E. coli but enhance it against MRSA?
Could combining cathelicidins with complementary functions create more effective antimicrobial therapies?

Common questions

What are cathelicidins and why are they important?

Cathelicidins are short, positively charged peptides that your immune system produces to fight infections. They can directly kill bacteria, neutralize bacterial toxins, and signal other immune cells to respond. Humans have one cathelicidin called LL-37, but other animals have different versions — and this study shows they don't all work the same way.

Why did MRSA-killing activity increase under more realistic conditions while E. coli killing decreased?

The researchers found this surprising result when testing under physiological salt concentrations (closer to real body conditions). The exact mechanism isn't fully explained, but it suggests that the way cathelicidins interact with gram-positive bacteria like MRSA is fundamentally different from how they interact with gram-negative bacteria like E. coli — and that standard lab conditions may underestimate their real-world effectiveness against MRSA.

Read the original research

Interspecies cathelicidin comparison reveals divergence in antimicrobial activity, TLR modulation, chemokine induction and regulation of phagocytosis.

Scientific reports, 7, 40874

View on PubMed ↗Publisher’s paper ↗

Citation

Coorens, Maarten; Scheenstra, Maaike R; Veldhuizen, Edwin J A; Haagsman, Henk P. (2017). Interspecies cathelicidin comparison reveals divergence in antimicrobial activity, TLR modulation, chemokine induction and regulation of phagocytosis.. Scientific reports, 7, 40874. https://doi.org/10.1038/srep40874