What Does Mast Cell Activation Syndrome Have to Do with Your Thyroid? Paloma Health Intestinal mast cellderived leukotrienes mediate the anaphylactic response to ingested antigens Science 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. 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.