Peptide Reference Desk
LL-37 antimicrobial assays: four controls that can reverse the conclusion
LL-37 results depend heavily on salt, serum, plastic binding and endotoxin. A sequence-confirmed peptide can still produce a misleading bioassay.
The assay environment is part of the result
LL-37 is a cationic host-defense peptide. Its apparent antimicrobial or immune activity can shift with ionic strength, serum proteins, medium composition and adsorption to labware. A paper that reports only peptide concentration leaves important context missing.
Four controls worth demanding
- Salt and medium: report composition, pH and inoculum rather than “buffer.”
- Serum or protein: note binding conditions that alter free peptide.
- Surface loss: control adsorption to tubes and plates.
- Endotoxin: test contamination before attributing immune readouts to LL-37.
Identity is necessary, not sufficient
LC-MS and HPLC can support sequence identity and purity. They do not establish folding state, aggregation, net peptide concentration or absence of biologically active contamination. For cell assays, endotoxin and vehicle controls may matter more than another decimal place in area purity.
A reproducible archive entry
Save organism or cell type, inoculum, medium, salt, serum, surface treatment, incubation time and endpoint. Without those fields, two “LL-37 activity” values may not be comparable at all.
Verify with primary records
Use the primary paper, current regulator label or lot-linked analytical file for the claim it supports. A search result is a route to evidence, not the evidence itself.