Mast cells: makers and breakers of allergic inflammation

Purpose of review Recent findings have developed, changed, challenged and extended the established view of mast cell biology and of their role in inflammation. The purpose of this review is to present and discuss recent research in this area relating to allergic inflammation. Recent findings Mast cells are traditionally viewed only as IgE-activated histamine-providing effector cells of allergic inflammation. Yet, recent findings also support a role for mast cells in the sensitization to allergens, and early released human mast cell tryptase has been shown to break down IgE, hence breaking the key maker of allergic inflammation. Furthermore, mast cells demonstrate proinflammatory action through nonhistamine and non-IgE-mediated routes. For example, the role of platelet-activating factor in contributing to allergic inflammation and anaphylaxis in mice is now starting to be shown in humans. Most surprisingly, mast cells have also emerged as modulators and downregulators of allergic inflammation. For example, the newly discovered siglec-8 receptor might act as an inhibitor of mast cell degranulation and thus of mast cell-mediated allergic inflammation. Also, mast cell-derived IL-10 is shown to be a modulator of allergic inflammation, demonstrated in a murine model of contact hypersensitivity. Summary Understanding the mast cell's divergent phenotypes based on situation and setting is required to truly discover their role in allergic inflammation.