The SARS-CoV-2 receptor-binding domain facilitates neutrophil transepithelial migration and nanoparticle uptake in the mice airways

SARS-CoV-2-induced infection is still dangerous. Mouse models are convenient to the investigation of virus-activated immune response mechanisms. However, mice are not proper model organisms to study COVID-19 due to decreased interaction affinity between the SARS-CoV-2 receptor-binding domain (RBD) and mouse angiotensin-converting enzyme 2 (ACE2) compared with human ACE2. In the present study, we propose a mouse model that allows estimating the influence of SARS-CoV-2 on the immune system. To mimic the effects of RBD-ACE2 high-affinity interaction, mice received the ACE2 inhibitor MLN-4760. To simulate virus loading, we applied 100 nm particles suspended in the solution of RBD via the oropharyngeal route to mice. In this model, MLN-4760 application enhanced neutrophil egress from the bone marrow to the bloodstream and RBD attracted neutrophils to the luminal side of the conducting airway epithelium. By contrast, inert 100 nm particles were not potent to stimulate neutrophil recruitment to the conducting airway mucosa. Using this model, and by altering the dosage of the ACE2 inhibitor, nanoparticles, and RBD, one can adapt it to investigate different COVID-19 states characterized with mild or severe airway inflammation. ### Competing Interest Statement The authors have declared no competing interest.