CD4 and Parkinson disease: For instance, modification of TBX21 and STAT4, which mediate primarily IL-12-induced Th1 differentiation, but not of STAT1, which is involved in IFN-γ-dependent reinforcement of the Th1 phenotype [39], might therefore indicate a preferential involvement of IL-12-dependent pathways and a minor, if any, role of IFN-γ signaling in the increased Th1 differentiation and function of CD4+ T cells occurring in PD patients.