IL4 and Alzheimer disease: Even though Th17 cells are not closely associated with Th1/Th2 balance, there is a significant correlation between the percentage of Th17 cells and IFN-γ-producing Th1 cells, but not IL-4-producing Th2 cells, suggesting Th17 cells work as an enhancer in the development of AD, but not an immune-polarizer (Koga et al., 2008).