Quantifying Intracellular Viral Pathogen: Specimen Preparation, Visualization and Quantification of Multiple Immunofluorescent Signals in Fixed Human Airway Epithelium Cultured at Air-Liquid Interface

Infection control and aggressive antibiotic therapy play an important role in the management of airway infections in individuals with cystic fibrosis (CF). The responses of airway epithelial cells to pathogens are likely to contribute to the pathobiology of CF lung disease. Primary airway epithelial cells obtained from individuals with CF, cultured and differentiated at air-liquid interface (ALI), effectively mimic the structure and function of the in vivo airway epithelium. With the recent respiratory viral pandemics, ALI cultures were extensively used to model respiratory infections in vitro to facilitate physiologically relevant respiratory research. Immunofluorescence staining and imaging were used as an effective tool to provide a fundamental understanding of host-pathogen interactions and for exploring the therapeutic potential of novel or repurposed drugs. Therefore, we described an optimized quantitative fluorescence microscopy assay for the wholemount staining and imaging of epithelial cell markers to identify distinct cell populations and pathogen-specific targets in ALI cultures of human airway epithelial cells grown on permeable support insert membranes. We present a detailed methodology using a graphical user interface (GUI) package to quantify the detected signals on a tiled whole membrane. Our method provided an imaging strategy of the entire membrane, overcoming the common issue of undersampling and enabling unbiased quantitative analysis.