Analysis of human lung mast cells by single cell RNA sequencing.

Mast cells are tissue-resident cells playing major roles in homeostasis and disease conditions. Lung mast cells are particularly important in airway inflammatory diseases such as asthma. Human mast cells are classically divided into the subsets MC and MC, where MC express the mast cell protease tryptase and MC in addition express chymase, carboxypeptidase A3 (CPA3) and cathepsin G. Apart from the disctintion of the MC and MC subsets, little is known about the heterogeniety of human lung mast cells and a deep analysis of their heterogeniety has previously not been performed. We therefore performed single cell RNA sequencing on sorted human lung mast cells using SmartSeq2. The mast cells showed high expression of classical mast cell markers. The expression of several individual genes varied considerably among the cells, however, no subpopulations were detected by unbiased clustering. Variable genes included the protease-encoding transcripts (chymase) and (cathepsin G). Human lung mast cells are predominantly of the MC subset and consistent with this, the expression of was only detectable in a small proportion of the cells, and correlated moderately to . However, in contrast to established data for the protein, mRNA was high in all cells and the correlation of to was weak.