Santa's Little Helper barrier, allowing the dog to understand Bart's commands, and consequently pass the obedience school. Santa's Little Helper has fathered several puppies. In "Two Dozen and One Greyhounds" (season six, 1995), he runs away to the dog racing track where he mates with a female hound named She's the Fastest. She later gives birth to 25 puppies and when the Simpsons cannot take care of them any longer, they decide to sell them; however, Mr. Burns steals the puppies and decides to make a tuxedo out of them. Before he does this, however, he becomes emotionally touched by them. This convinces
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,