Analysis of epithelial barrier integrity in polarized lung epithelial cells.

Epithelial surfaces of the body are a key component of host defense by providing a mechanical barrier against potentially harmful substances. The respiratory tract is constantly challenged by a wide range of airborne pathogens and particulates, and provides not only a mucosal barrier, but also an intricate innate immune defense system. Disruption of the alveolar epithelial barrier can lead to acute lung injury, pneumonia, and acute respiratory distress syndrome. Protection of lung epithelial integrity, or repair of hyperpermeability with keratinocyte growth factor or Hsp90 inhibitors, is crucial for combating permeability edema. Ex vivo-differentiated lung epithelium represents a physiologically relevant tool for analyzing the effect of pathogens, chemicals, or drugs on lung barrier function. The integrity of the lung epithelial layer can be determined by several approaches. By combining two of these techniques, transepithelial electrical resistance and paracellular flux of fluorescent molecules, information about barrier integrity can be obtained in a prompt and convenient manner. As example, the virus- or bacterial toxin-mediated disruption of an ex vivo-differentiated mucociliary lung epithelial barrier is used here for assessing advantages and limitations of these methods.