Since the seminal description implicating Mas-linked G protein-coupled receptor X2 (MRGPRX2) occupancy in the degranulation of mast cells (MCs) by drugs, many studies have been undertaken on this potential new endotype of immediate drug hypersensitivity reactions (IDHRs). However, current evidence for this mechanism comes mainly from animal (mutant) models or in-vitro studies. Irrefutable clinical evidence in humans is lacking. Furthermore, translating these preclinical results into clinical relevance in humans is difficult and needs to be interpreted critically. Based on our clinical priorities and our experience with functional analyses of basophils, MCs and T lymphocytes, the aim of my presentation is to propose a theoretical mechanistic algorithm that could facilitate discrimination between MC degranulation due to MRGPRX2 receptor activation and bridging of specific IgE antibodies coupled to the FceRI receptor. Special focus will be paid to the role of in vitro/ex vivo cellular tests.
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