Scientists have not discovered exactly how prions work. Current research shows that prions accumulate in lysosomes. In the brain, it is possible that the filled lysosomes burst and damage cells. As diseased cells die, the prions contained in the cells are released and are able to attack other cells. It is thought that prions are responsible for the group of brain diseases known as transmissible spongiform encephalopathies (TSEs). This group includes the disease that is referred to as bovine spongiform encephalopathy (mad cow disease) when it occurs in cattle and Creutzfeldt-Jakob disease when it occurs in humans.