Chronic dysregulated influx of neutrophil into the airway increases neutrophil burden and augments the inflammatory processes often observed in diseases such as cystic fibrosis. The quantification of neutrophil influx is often accomplished with the use of destructive tests such as imaging cytometry and myeloperoxidase assay. However, those methods are unable to capture information about the cascade of events that precede trans-epithelium migration. In this work, we employed a high resolution micro-optical coherence tomography (µOCT) technology to perform real time imaging of neutrophil activity across airway epithelial cells grown on the underside of Transwell permeable supports. This inverted configuration allows the creation of an air-liquid interface at the apical side of the cells. The µOCT imaging technology, based on the principles of spectral-domain OCT, has a lateral and axial resolution of 2 and 1.3µm, respectively. In addition, it has an axial range of approximately 300µm and is capable of recording cross-sectional images at 40 fps. By raster scanning the illumination beam, the behavior of the neutrophils across a 3D volume can be recorded over time. Thus, this imaging modality is capable of resolving individual neutrophils and, potentially, capturing the cascading events involving neutrophil tethering, subsequent adhesion to activated epithelial cells and the ultimate passage through the epithelial cells to the air space on the apical side. As a result, not only can the amount of neutrophil migration be quantified, how neutrophils behave, organize and interact with the epithelial cells and each other can also be more closely analyzed by µOCT imaging.
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