What is Mast Cell Activation Syndrome? Longevity Health Histamine and TH2 cytokines regulate the biosynthesis of cysteinyl leukotrienes and expression of their receptors in human mast cells Inflammation Research Springer Nature Link Olive leaf extract (OLE) reduces mast cell mediated allergic inflammation ScienceDirect 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.