News in Cellular Allergology: A Review of the Human Mast Cell and Basophil Granulocyte Literature from January 2013 to May 2015.

Mast cell activation releases the mediators associated with type I allergy. As such, the study of mast cell activation is critical for understanding the allergic reaction, and for developing methods to control it. Importantly, another ligand receptor pair (compound 48/80 and MRGPRX2) that activates mast cells in addition to allergen-IgE-FcεRI has been identified. As mast cells mature in tissue from hematopoietic stem cells, their physiology and pathophysiology is difficult to study. Mast cell lines and mast cells cultured from stem cells are often studied instead of tissue mast cells. There has been some progress in the description of the mechanism of the activation of mast cells, substances limiting mast cell activation and in the catalogue of proteases that mast cells express. Basophil granulocytes express FcεRI, bind IgE and respond to allergen crosslinking in a very similar fashion to mast cells. In the recent literature, basophils were mistakenly described as antigen-presenting cells; this has convincingly been disputed in a number of subsequent publications. Their function in physiology and pathophysiology is not known, but they are frequently used to document allergic sensitisation in the basophil activation test. Significant progress has been made in documenting the relevance of basophil activation as a second-line test in allergy diagnosis. Basophil reactivity and sensitivity may reflect symptom severity and allergen threshold, and are used to document and monitor allergy. The physiology and pathophysiology of allergic effector cells remain an important area of research.