Activated mammalian CD4+ T helper cells produce cytokines that result in either a Th1 response that is directed toward
cell-mediated and inflammation responses, and induces macrophages to kill intracellular pathogens such as mycobacteria or salmonella (Kagaya et al., 1989), or a Th2 response that leads to the production by B cells of antibodies that react with extracellular pathogens such as streptococci (Lebman and Coffman, 1988).