Detecting Changes in Mast Cell Numbers Versus Activation in Human Disease: A Roadblock for Current Biomarkers? ScienceDirect Information about Mast Cell Activation Syndrome, MCAS Mast cell specific CysLT2 receptor signaling inhibits cysteinyl leukotriene dependent mast cell activation and type 2 allergic lung inflammation: Cell Reports Mast cell activation syndrome, neck pain and the vagus nerve 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.