IFNG and Parkinson disease: In the study by Williams et al. [73], when mice were injected with adeno-associated virus 2 (AAV2)-synaptophysin (SYN) 4 weeks after the detection of T cell activation and corresponsive factors expression, it was found that the expression of transcription factors T-bet and Foxp3, cytokines interferon gamma (IFN-γ), and IL-10 in each of Th1 and Treg cells showed a significant increase, which indicated that both Th1 and Treg cell activation levels in the early stage of PD development showed an increase.