Supplementary Material for: <b><i>Staphylococcus epidermidis</i></b> Activates Aryl Hydrocarbon Receptor Signaling in Human Keratinocytes: Implications for Cutaneous Defense

Bacterial challenge of keratinocytes with the abundant skin commensal <i>Staphylococcus epidermidis</i> induces distinct innate immune responses, but the underlying molecular mechanisms are still emerging. We report that the aryl hydrocarbon receptor (AhR) was activated in human primary keratinocytes infected with <i>S. epidermidis</i>, leading to induction of the AhR-responsive gene cytochrome P450 1A1 (CYP1A1). In addition, functional AhR was required for <i>S. epidermidis</i>-mediated induction of IL-1β expression in keratinocytes. AhR-dependent gene induction of IL-1β and CYP1A1 was mediated by factor(s) &lt; 2 kDa secreted by <i>S. epidermidis</i>. Blockade of the AhR in a 3D organotypic skin equivalent infected with <i>S. epidermidis</i> attenuated the <i>S. epidermidis</i>-induced CYP1A1 and IL-1β expression. Moreover, <i>S. epidermidis</i> also induced expression of IL-1α and of the antimicrobial peptide human β-defensin-3 in an AhR-dependent manner in a 3D skin equivalent. An increased outgrowth of <i>S. epidermidis</i> on the surface of skin explants treated with a specific AhR inhibitor further indicate a pivotal role of the AhR in mediating an epidermal defense response. Taken together, our data expand the role of the AhR in innate immunity and support a previously unappreciated contribution for the AhR in cutaneous defense.