Mast cells are strongly implicated in the pathogenesis of allergies and asthma. However, the role of different mast cell populations and how they are regulated remains unclear. We hypothesize that there is a heterogeneity among mast cells that is regulated through interactions with neighboring cells and we aim to characterize this by single cell RNA sequencing (scRNAseq). We hope to define novel mast cell subpopulations that will be investigated for functional differences. To elucidate the interactions with neighboring cells that regulate mast cell heterogeneity, receptor-ligand expression will be investigated in different tissues. This project has the potential to discover functionally different novel mast cell subpopulations and novel cell-cell interactions that can have an impact on diseases were mast cells play a central role, such as allergies, asthma and mastocytosis. The end goal is to specifically be able to inhibit pathogenic mast cell subsets in disease.