So CD four T cells can also bind to APts such as macrophages and dendritic cells and they release these chemicals known as lymphocines. And these lymphocines will stimulate our cell mediated immunity. And that means it will call upon other macrophages, other wide blood cells that will come to that infected area and begin our defensive mechanism response engulfing those pathogenic agents. So our CD four T cells can either stimulate the humoral immunity or they can stimulate the cell mediated immunity. On the other hand, as we'll see in just a moment, the CDAT cells can only stimulate the cell mediated immunity. So what exactly is a CDAT cell?