Human Cathelicidin LL - 37 in Oral Keratinocyte Proliferation

Host defence peptides (HDPs), synthesised by phagocytic cells or secreted by epithelia in response to inflammation and infection, are a diverse group of small cationic peptides with varied activity against a range of bacteria, fungi and viruses. Originally characterised by their antimicrobial properties, HDPs are now known to be multi-functional and may be important in host defence as signalling molecules communicating between the innate and adaptive immune systems. Insect derived HDPs have been shown to kill tumour cell lines and to increase survival of mice in a peritoneal tumour model. á defensins have been shown to increase proliferation in some epithelial cells but the role of HDPs in tumour progression is still unclear.

Objectives: The aim of this study was to determine the effect of LL-37, a HDP primarily located within neutrophils and secreted by epithelial cells, on proliferation in malignant and non-malignant oral epithelial cell lines.

Methods: Human oral keratinocyte cells from two malignant cell lines (H357, H376) and a non-malignant cell line (DOK) were cultured into 96 well plates under standard tissue conditions. Cells were seeded in complete medium for 24h and then incubated in serum free conditions for 16h. Cells were then incubated in 0%, 1% or 10% serum conditions with 0-100µg/mL LL-37 for up to 24h. The number of proliferating viable cells was then assessed using the Celltiter 96 aqueous one solution cell proliferation assay (Promega, USA).

Results: LL-37 decreased cell proliferation at concentrations >50µg/mL for all cell lines. Cells in serum-free culture were more sensitive to the effects of peptide in all cases.

Conclusion: LL-37 decreased proliferation of malignant and non-malignant human cell lines. This effect was dependent on serum in the medium. It is not known if this was due to binding or degradation of the HDP or the effects of serum on cells.