Unlocking mast cell diversity in human nasal polyps

Mast Cells (MCs) infiltrate the nasal polyps of patients with chronic rhinosinusitis (CRS) and the bronchial mucosa of patients with mild, moderate, and severe asthma. MCs are a significant source of IL-33-elicited Th2 cytokines in the sputum of asthmatics and upon activation generate or release high levels of mediators including tryptase, histamine, and prostaglandin D2. Although airway MC heterogeneity can readily identified through protease immunostaining and tissue sub-localization, the functional distinctions and developmental relationships between MC subsets remain uncertain, in part because of the lack of flow cytometric markers to distinguish them and technical difficulties in isolating MCs. Using a novel flow cytometric approach we have identified several distinct MC subsets in the nasal polyps of patients with CRS that vary in expression of FcER1, c-kit, B7, CD203 and chymase. Nasal polyp MCs were further characterized through unbiased single cell RNA sequencing, revealing heterogeneity within the MC population and providing novel insight into transcriptional differences between these subsets.

Cholesterol, Inflammasomes, and Atherogenesis

Plasma cholesterol levels have been strongly associated with atherogenesis, underscoring the role of lipid metabolism in defining cardiovascular disease risk. However, atherosclerotic plaque is highly dynamic and contains elements of both the innate and adaptive immune system that respond to the aberrant accumulation of lipids in the subendothelial space. Previous research has focused on defining how proinflammatory cytokines synthesized by macrophages, such as interleukin-1β (IL-1β), modulate the progression of atherosclerosis, supporting the notion that chronic inflammation accelerates atherogenesis. More recently, emphasis has been placed on the elucidation of the mechanisms that contribute to pro-IL-1β production and finally its processing via multiprotein complexes termed the inflammasomes, a family of cytosolic multiprotein complexes that serve as sensors of either pathogen invasion or cellular stress (ie, cholesterol crystals) and work via triggering caspase-1-mediated processing of pro-IL-1β to IL-1β. Based on this link between cholesterol metabolism, NLRP3 inflammasome activation, and IL-1β release, it is important to re-evaluate how the atherogenic environment stimulates immune cells to produce IL-1β.