Santa's Little Helper event; however, their plan fails and a drunk shark that's discovered at the event becomes the new mascot instead. Santa's Little Helper gladly returns to the Simpson family. Santa's Little Helper's initial appearance on "The Simpsons" was in the first episode of the series, "Simpsons Roasting on an Open Fire", which aired on Dec. 17, 1989. Since then, he has become a recurring character. "The Simpsons" creator Matt Groening told "TV Guide" in 2000 that "we [the staff] painted ourselves into a corner with our Christmas episode. Once we wrote the dog into the show, we were stuck with him."
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,