Figure 1: Schema of immune balance. Two subtypes of T-helper cells were found to have differences in cytokine secretion pattern and other functions, which indicated that Th1 and Th2 cells were important regulators of immune response. Th1 cells are hypothesized to lead the attack against intracellular pathogens and Th2 cells are believed to emphasize protection against extracellular pathogens. And more recently, a new subset of helper T-cells, called Th17, was described. Th1, Th2 and Th17 subsets are produced from a non-committed population of precursor naïve T cells. The schema was identified in our previous report, ref [26].