The brain does not have immune cells that fight infection. Instead, it has microglia that regulate immunity in the brain. Mast cells surround the blood brain barrier, which protects the brain against toxins and pathogens. Therefore, that makes mast cells the brain gatekeepers. They control the blood brain barrier that allow molecules into the brain that activate the microglia. When microglia increase, we see inflammation in the brain. Interestingly, increased microglia have been found in the bra