# Antimicrobial peptide LL-37 increases rhinovirus-induced interferon β expression in human airway epithelial cells through a Ca2+-dependent mechanism

## TL;DR

The antimicrobial peptide LL-37 boosts the immune response to rhinovirus in airway cells by increasing interferon β production through a calcium-dependent process.

## Contribution

LL-37 enhances IFNβ expression via a Ca2+-dependent mechanism, independent of classical viral receptors.

## Key findings

- LL-37 reduces rhinovirus load in human airway epithelial cells.
- LL-37 increases rhinovirus-induced IFNβ mRNA expression.
- Calcium is essential for LL-37's effect on IFNβ expression.

## Abstract

The human cathelicidin LL-37 is active against both bacteria and viruses, but it also shows immunomodulatory properties. Here, we assess the impact of LL-37 on viral signaling in human airway epithelial BEAS-2B cells infected with the respiratory pathogen rhinovirus (RV). We show that LL-37 (4 μM) enhances RV-induced expression of interferon β (IFNβ) transcript and reduces viral-load. LL-37-evoked potentiation of RV-stimulated IFNβ does not involve up-regulation of the classical viral TLR3, MDA5 and RIG-I receptors. Moreover, the LL-37-induced stimulation of IFNβ expression in the presence of RV is abolished by chloroquine, an inhibitor of endosomal acidification. Interestingly, RV + LL-37-induced stimulation of IFNβ is observed in the absence but not in the presence of the Ca2+ chelating agent EGTA, indicating that Ca2+ is critical for this effect. Indeed, we demonstrate that LL-37 increases intracellular [Ca2+] in cells loaded with the fluorescent Ca2+ indicator Fluo-4 AM. Furthermore, we reveal that treatment with RV in combination with the Ca2+ ionophore A23187 promotes IFNβ expression, showing the importance of Ca2+. In conclusion, we demonstrate that LL-37 acts in synergy with RV to enhance IFNβ expression and that this effect involves LL-37-induced increase in intracellular [Ca2+].

•LL-37 reduces rhinovirus-load in human airway epithelial cells.•LL-37 potentiates rhinovirus-induced IFNβ mRNA expression.•Inhibition of endosomal acidification abolishes LL-37-induced potentiation of IFNβ•LL-37 elevates intracellular [Ca2+].•LL-37-induced potentiation of IFNβ is observed in presence but not absence of Ca2+.

LL-37 reduces rhinovirus-load in human airway epithelial cells.

LL-37 potentiates rhinovirus-induced IFNβ mRNA expression.

Inhibition of endosomal acidification abolishes LL-37-induced potentiation of IFNβ

LL-37 elevates intracellular [Ca2+].

LL-37-induced potentiation of IFNβ is observed in presence but not absence of Ca2+.