Epithelial differentiation is a determinant in the production of eotaxin-2 and -3 by bronchial epithelial cells in response to IL-4 and IL-13.

The composition of the airway epithelium is dynamic and epithelial differentiation is regulated by endogenous mediators as well as inhaled substances. In atopic asthma the differentiation of the epithelium is altered. Various studies have addressed the ability of cultured airway epithelial cells to release the eosinophil-attractant chemokines eotaxin, eotaxin-2 and eotaxin-3 using epithelial cell lines or poorly differentiated primary cells. Since little is known about the role of the epithelial differentiation state in the response of epithelial cells to stimuli that increase production of mediators such as the eotaxins, we analyzed the effect of differentiation state on the production of the eotaxins. In particular, we investigated the effects of the Th2 cytokines IL-4 and IL-13 on eotaxin-2 and -3 production by primary human bronchial epithelial cells and examined whether their production is affected by epithelial cell differentiation using both submerged and air-liquid interface (ALI) cultures. The results show that both IL-4 and IL-13 increase eotaxin-2 and -3 mRNA expression and protein release in submerged- and ALI-cultures. Moreover, epithelial differentiation in ALI-cultures appeared an important determinant in the regulation of eotaxin-2 and -3. Mucociliary differentiation of the epithelial cells was induced by culture in the presence of a high concentration of retinoic acid (RA), whereas low concentrations of RA resulted in a flattened squamous epithelial phenotype. Mucociliary differentiated ALI-cultures expressed and released more eotaxin-3 upon stimulation with IL-4/IL-13, whereas eotaxin-2 production was predominantly found in squamous differentiated ALI-cultures. TNFalpha reduced IL-4-induced eotaxin-2 release in submerged cultures but not in ALI-cultures; no effects on eotaxin-3 synthesis were observed. The results indicate that epithelial differentiation is an important determinant in Th2 cytokine-induced eotaxin-2 and -3 release by airway epithelial cells. These findings may provide new insights into the role of airway epithelial differentiation and Th2 cytokines in the pathogenesis of inflammatory lung disorders such as asthma.

Rhinovirus increases human beta-defensin-2 and -3 mRNA expression in cultured bronchial epithelial cells.

Human beta-defensins (hBDs) are antimicrobial peptides that play important roles in host defense against infection, inflammation and immunity. Previous studies showed that micro-organisms and proinflammatory mediators regulate the expression of these peptides in airway epithelial cells. The aim of the present study was to investigate the modulation of expression of hBDs in cultured primary bronchial epithelial cells (PBEC) by rhinovirus-16 (RV16), a respiratory virus responsible for the common cold and associated with asthma exacerbations. RV16 was found to induce expression of hBD-2 and -3 mRNA in PBEC, but did not affect hBD-1 mRNA. Viral replication appeared essential for rhinovirus-induced beta-defensin mRNA expression, since UV-inactivated rhinovirus did not increase expression of hBD-2 and hBD-3 mRNA. Exposure to synthetic double-stranded RNA (dsRNA) molecule polyinosinic:polycytidylic acid had a similar effect as RV16 on mRNA expression of these peptides in PBEC. In line with this, PBEC were found to express TLR3, a Toll-like receptor involved in recognition of dsRNA. This study shows that rhinovirus infection of PBEC leads to increased hBD-2 and hBD-3 mRNA expression, which may play a role in both the uncomplicated common cold and in virus-associated exacerbations of asthma.