Epithelium samples were obtained by brushing the trachea, large airway epithelium (LAE), and small airway epithelium (SAE).  Expression was quantified using Affymetrix HG-U133 Plus 2.0 microarrays.  It was observed that all parts of the tracheobronchial tree express ACE2 in normal health with the trachea and LAE expressing it more than the SAE.  

Michigan State University

- expression in the tracheobronchial tree
- expression in primary basal cells
- expression by cell type in the small airway

ACE2 Expression in the Airway Epithelium of Healthy Nonsmokers

Zhang, H., Rostami, M. R., Leopold, P. L., Mezey, J. G., O'Beirne, S. L., Strulovici-Barel, Y., & Crystal, R. G. (2020). Expression of the SARS-CoV-2 ACE2 Receptor in the Human Airway Epithelium. American Journal of Respiratory and Critical Care Medicine, (ja).
https://www.atsjournals.org/doi/full/10.1164/rccm.202003-0541OC
doi: 10.1164/rccm.202003-0541OC   

Expression of the SARS-CoV-2 ACE2 Receptor in the Human Airway Epithelium

Each datapoint represents a single cell.  All major cell types of the small airway epithelium (SAE), including basal cells, intermediate cells, club cells, mucus cells, and ciliated cells, express ACE2.  Because of technology limitations, only 1-2% of all of the tested cells were found to express ACE2.  It is thought that cells expressing lower amounts of the enzyme went uncounted, and these reported data are an underrepresentation of the number of cells that express ACE2.  

ACE2 is Expressed in Major Cell Types in the Small Airway Epithelium

RNA samples were obtained by brushing tracheal basal cells (BCs) on day 0.  Cell colonies were then created on an air–liquid interface culture, and additional samples were taken every 7 days.  ACE2 expression levels were determined using Affymetrix HG-U133 Plus 2.0 microarrays.  It was found that as primary basal cells, which are the precursors for other epithelial cells, differentiate into these said cells, their ACE2 expression significantly increases (p < 10^-5).  

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