Receptor-binding domain of SARS-CoV-2 facilitates internalization of 100 nm particles by neutrophils in conducting airway mucosa of mice.

Abstract

Neutrophils and NETs are implicated in the pathogenesis of SARS-CoV2-induced inflammation; however, the factors that trigger neutrophil migration are still poorly investigated. The study aimed to detect whether receptor-binding domain of SARS-CoV-2 (RBD) is potent to attract neutrophils to conducting airway mucosa and to facilitate uptake of 100 nm particles.

Mice received an oropharyngeal application of fluorescent 100 nm particles suspended either in phosphate buffer or in 0.1% RBD solution. Control groups received particles in 0.1% BSA, 0.1% of RBD and BSA solution. 24 hours after, lungs were PFA-fixed and whole-mount conducting airways were subjected to immunohistochemistry. Three-dimensional images were obtained using confocal microscopy. Quantitative image analysis was performed to estimate the number and ingestion activity of neutrophils in conducting airway mucosa.

100 nm particles applied to mice in phosphate buffer did not induce neutrophil migration to conducting airway. Particles were mostly internalized by CD169+ cells in the luminal side of the epithelium. RBD induced neutrophil migration to conducting airway mucosa and to the luminal side of the airway epithelium. On the luminal side, neutrophils formed clusters around CD169+ cells that internalized particles. Neutrophils also contributed to particle internalization.

Thus, RBD stimulates neutrophil recruitment to conducting airway mucosa - the site of the pathogen entrance to the organism, that makes possible neutrophil-particle interaction.

The work was supported by RFBR, project 20-04-60311