Revisiting the role of the mast cell in asthma

Purpose of reviewIn humans, mast cells are ubiquitously present in tissues adjacent to external environment and consequently have an important sentential role in host defence, homeostasis and repair. Their key role in allergen-mediated conditions has been recognized for many decades already. So far, therapies targeting mast cells offered clinical efficacy in allergic conditions except for asthma. More recently, sophisticated sampling and detection techniques revealed pleiotrophic immunological and functional properties of mast cells in and beyond asthma with potential clinical and management implications. These findings bring back the mast cell as a key player in the field of asthma and warrant a review of the recent literature.Recent findingsThe heterogeneity of human mast cells has been recognized: MCTC expressing both tryptase and chymase and MCT expressing tryptase only. Apart from this subphenotyping, mast cells may comprise and produce several other mediators and cytokines. Their immunological and functional properties depend on their (co)localization within the human body and can alter under changing conditions (e.g. pathogens, allergens, etc). Recent data revealed a novel mast cell phenotype within the alveolar tissue of patients with asthma. Increasing evidence shows a key role for alveolar mast cells in the pathophysiology of viral respiratory infections and in the development of allergen sensitization and asthma.SummaryIncreasing evidence points toward a key role of mast cells in the pathophysiology and pathogenesis of asthma and this warrants further investigation and the development of effective targeted therapies.