Studies have shown that CD4 + Teffs (such as Th1 and Th17) are involved in the process of neuron degeneration (such as in PD and MS) and maintain and accelerate the proinflammatory M1 phenotype of microglia by secreting proinflammatory phenotypic factors L17, IFN-γ, and granules B (Fig. 2) [45, 92, 98]. Here, CD4 is linked to Parkinson disease.