In this review, we focus on the analysis of the interplay of the different sub-populations of CD4+ T-cells infiltrating the CNS and how they participate in regulating the outcome of neuroinflammation and neurodegeneration in the context of Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis and multiple sclerosis. Here, CD4 is linked to early-onset autosomal dominant Alzheimer disease.