Santa's Little Helper the dog was a "sympathetic" character. Welker has been praised by staff members for his performances on the show. David Mirkin has noted that "he can do anything, and it fits perfectly. You forget you're listening to a guy, and he's a pleasure to work with." Groening has commented that he was "unbelievably good" at doing animal noises. After 1995, Castellaneta voiced Santa's Little Helper on his own while Welker performed other animal noises until his full departure in 2002, when he was denied a pay raise. In the "questions and answers" section on his website, Welker revealed that the
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,