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The airway epithelium forms a barrier against infection but also produces antimicrobial peptides (AMPs) and other inflammatory mediators to activate the immune system. It has been shown that in allergic disorders, Th2 cytokines may hamper the antimicrobial activity of the epithelium. However, the presence of Th2 cytokines also affects the composition of the epithelial layer which may alter its function. Therefore, we investigated whether exposure of human primary bronchial epithelial cells (PBEC) to Th2 cytokines during mucociliary differentiation affects expression of the human cathelicidin antimicrobial protein (hCAP18)/LL-37 and human beta defensins (hBD), and antimicrobial activity.PBEC were cultured at an air-liquid interface (ALI) for two weeks in the presence of various concentrations of IL-4 or IL-13. Changes in differentiation and in expression of various AMPs and the antimicrobial proteinase inhibitors secretory leukocyte protease inhibitor (SLPI) and elafin were investigated as well as antimicrobial activity.IL-4 and IL-13 increased mRNA expression of hCAP18/LL-37 and hBD-2. Dot blot analysis also showed an increase in hCAP18/LL-37 protein in apical washes of IL-4-treated ALI cultures, whereas Western Blot analysis showed expression of a protein of approximately 4.5 kDa in basal medium of IL-4-treated cultures. Using sandwich ELISA we found that also hBD-2 in apical washes was increased by both IL-4 and IL-13. SLPI and elafin levels were not affected by IL-4 or IL-13 at the mRNA or protein level. Apical wash obtained from IL-4- and IL-13-treated cultures displayed increased antimicrobial activity against Pseudomonas aeruginosa compared to medium-treated cultures. In addition, differentiation in the presence of Th2 cytokines resulted in increased MUC5AC production as has been shown previously.These data suggest that prolonged exposure to Th2 cytokines during mucociliary differentiation contributes to antimicrobial defence by increasing the expression and release of selected antimicrobial peptides and mucus.

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.

Background: Increased airway epithelial proliferation is frequently observed in smokers. To elucidate the molecular mechanisms leading to these epithelial changes, we studied the effect of cigarette smoke condensate (CSC) on cell proliferation, wound closure and mitogen activated protein kinase (MAPK) activation. We also studied whether modulation of intracellular glutathione/thiol levels could attenuate CSC-induced cell proliferation., Methods: Cells of the bronchial epithelial cell line NCI-H292 and subcultures of primary bronchial epithelial cells were used for the present study. The effect of CSC on epithelial proliferation was assessed using 5-bromo-2-deoxyuridine (BrdU) incorporation. Modulation of epithelial wound repair was studied by analysis of closure of 3 mm circular scrape wounds during 72 hours of culture. Wound closure was calculated from digital images obtained at 24 h intervals. Activation of mitogen-activated protein kinases was assessed by Western blotting using phospho-specific antibodies., Results: At low concentrations CSC increased proliferation of NCI-H292 cells, whereas high concentrations were inhibitory as a result of cytotoxicity. Low concentrations of CSC also increased epithelial wound closure of both NCI-H292 and PBEC, whereas at high concentrations closure was inhibited. At low, mitogenic concentrations, CSC caused persistent activation of ERK1/2, a MAPK involved in cell proliferation. Inhibition of cell proliferation by high concentrations of CSC was associated with activation of the pro-apoptotic MAP kinases p38 and JNK. Modulation of intracellular glutathione (GSH)/thiol levels using N-acetyl-L-cysteine, GSH or buthionine sulphoximine (BSO), demonstrated that both the stimulatory and the inhibitory effects of CSC were regulated in part by intracellular GSH levels., Conclusion: These results indicate that CSC may increase cell proliferation and wound closure dependent on the local concentration of cigarette smoke and the anti-oxidant status. These findings are consistent with increased epithelial proliferation in smokers, and may provide further insight in the development of lung cancer.

Human airways are frequently exposed to potentially harmful agents that cause tissue injury. Upon such injury, a repair process is initiated that comprises cell migration, proliferation, and differentiation. We have previously shown that human neutrophil defensins (human neutrophil peptides 1-3 [HNP1-3]) induce airway epithelial cell proliferation. Because of the role of cell proliferation in epithelial wound repair, we investigated the effect of HNP1-3 on airway epithelial wound closure and mucin gene expression in vitro. Using NCI-H292 airway epithelial cell cultures, we demonstrated that HNP1-3 cause a dose- and time-dependent increase of wound closure as well as increased cell migration. Furthermore, HNP1-3 caused a biphasic activation of the mitogen-activated protein kinase extracellular-regulated kinase 1 and 2 (ERK1/2). Both the effects of HNP1-3 on wound closure and ERK1/2 activation were blocked by specific inhibitors of the mitogen-activated protein kinase kinase MEK, whereas inhibitors of epidermal growth factor receptor tyrosine kinase, phosphatidylinositol 3-kinase, and Src did block defensin-enhanced wound closure but not ERK1/2 activation. Finally, HNP1-3 increased mRNA encoding the mucins MUC5B and MUC5AC, suggesting a role for defensins in mucous cell differentiation. These results indicate that neutrophil defensins increase epithelial wound repair in vitro, which involves migration and proliferation, and mucin production. Neutrophil defensin-enhanced wound repair appears to require epidermal growth factor receptor activation and downstream signaling pathways.

Investigates the effect of defensins on the production of secretory leukocyte proteinase inhibitor (SLPI) and the related neutrophil elastase (NE) inhibitor elafin/SKALP in primary bronchial epithelial cells (PBEC). Suggestion of a role for defensins in the dynamic regulation of the antiproteinase screen in the lung at sites of inflammation.

Investigates whether defensins, the most abundant components of the azurophilic granule of neutrophils, induce interleukin-8 (IL-8) expression in airway epithelial cells and local chemokine networks. Purification and characterization of defensins; Effect of defensins on IL-8 protein secretion and mRNA expression.