Mast Cell Activation Syndrome: Symptoms, Causes, Diagnosis, and Treatment Mast cells are hypersensitive immune cells that release histamine and other inflammatory mediatorsoften in response to oxidative stress, environmental toxins, and immune imbalance. Many patients with MCAS have low levels of glutathione. Lipid orchestrated paracrine circuit coordinates mast cell maturation and anaphylaxis through functional interaction with fibroblasts ScienceDirect AAAAI Mast Cell Disorders Committee Work Group Report: Mast cell activation syndrome (MCAS) diagnosis and management Journal of Allergy and Clinical Immunology