IκBζ is constitutively expressed in human and murine airway epithelium

ABSTRACT AIM IκBζ is a transcriptional factor induced in immune cells upon Toll-like receptor (TLR) activation. Recent studies demonstrate unconventional, constitutive expression of IκBζ in epithelium of mouse skin and eyes, possibly reflecting continuous activation of TLRs by pathogen-associated molecular patterns (PAMPs). In this context, the lung epithelium which constitutes another important barrier also expresses IκBζ but may not be as actively exposed to pathogens as skin and eyes. Our aim was to determine if IκBζ expression in the lungs is constitutive or induced. SIGNIFICANCE IκBζ is linked to lung disorders due to its role in regulating protective cytokines and antimicrobial peptides in airway epithelium and can therefore be a potential biomarker and a key therapeutic target. METHODS We evaluated IκBζ expression in airway epithelia of healthy humans and three kinds of mice: normal, gnotobiotic and Nfkbiz −/− knockout, using immunostaining and immunoblotting. RESULTS Immunohistochemistry of ciliated airway epithelial cells in healthy humans and normal mice was positive for IκBζ. The pathogen free airway cells from gnotobiotic mice also stained positive, suggesting that lung epithelial IκBζ expression does not require induction by PAMPs. Although lung epithelia from Nfkbiz −/− knockout mice also stained positive, this knockout may not have eliminated exons 3-4 and 9-14, and so did not provide the specificity control for the IκBζ antiserum. Importantly, immunoblotting tissue homogenates from gnotobiotic mouse lungs and primary human airway epithelial cells demonstrated constitutive IκBζ expression at its correct 86 kDa size. CONCLUSIONS Our data demonstrates constitutive expression of IκBζ protein in airway epithelium, indicating a potential role for this molecule in lung homeostasis.