Santa's Little Helper of their sacrifices and starts treating him badly, causing him to run away. He ends up in the possession of Mr. Burns, who trains him to become a vicious attack dog. Several days later, Bart stumbles upon the trained Santa's Little Helper and is attacked, but the greyhound eventually recognizes his old friend and stops. In "The Canine Mutiny" (season eight, 1997), Bart uses a fake charge card to buy a well-trained rough collie named Laddie from a mail-order catalog. Laddie learns many tricks that Santa's Little Helper is completely unable to perform, and the Simpson family nearly forgets about
T helper cell because such knowledge may be very useful in the treatment of disease and in increasing the effectiveness of vaccination. Proliferating helper T cells that develop into effector T cells differentiate into two major subtypes of cells known as T1 and T2 cells (also known as Type 1 and Type 2 helper T cells, respectively). T1 helper cells lead to an increased cell-mediated response, typically against intracellular bacteria and protozoa. They are triggered by IL-12 and their effector cytokines are IFN-γ and IL-2. The main effector cells of T1 immunity are macrophages as well as CD8 T cells, IgG B cells,