[Mast Cells Activation Syndrome: Clinical Spectrum, Diagnosis and Treatment].

Mast cells are key components of the innate immune system and play a central role in the "classical" allergic response. These cells are predominantly located in the skin, mucosal tissues, respiratory tract, and gastrointestinal system. Their cytoplasmic granules contain a variety of potent mediators such as histamine, tryptase, heparin, and cytokines - that are released upon activation and are responsible for hallmark allergic symptoms, including urticaria, bronchospasm, and anaphylaxis. In most cases, mast cell activation occurs via allergen exposure leading to cross-linking of IgE bound to high-affinity FcεRI receptors. However, in patients with recurrent episodes of symptoms/signs suggestive of mast cell activation, Mast Cell Activation Syndrome (MCAS) should be considered. This diagnosis encompasses a spectrum of underlying activation pathways and is established through a combination of clinical features and laboratory findings.