CD86 and Parkinson disease: The increased expression of activation markers in microglia like MHC-II and CD86, which provide, respectively, the first and costimulatory signals necessary for T cell activation, coupled with the increased percentages of peripheral T cells in both brain areas suggest the establishment of an immunological synapse in key areas involved in PD pathology which could drive and sustain neuroinflammation and lead to neurodegeneration.