MHCII Is Required for  -Synuclein-Induced Activation of Microglia, CD4 T Cell Proliferation, and Dopaminergic Neurodegeneration

Accumulation of α-synuclein (α-syn) in the brain is a core feature of Parkinson disease (PD) and leads to microglial activation, production of inflammatory cytokines and chemokines, T-cell infiltration, and neurodegeneration. Here, we have used both an <i>in vivo</i> mouse model induced by viral overexpression of α-syn as well as <i>in vitro</i> systems to study the role of the MHCII complex in α-syn-induced neuroinflammation and neurodegeneration. We find that <i>in vivo</i>, expression of full-length human α-syn causes striking induction of MHCII expression by microglia, while knock-out of MHCII prevents α-syn-induced microglial activation, antigen presentation, IgG deposition, and the degeneration of dopaminergic neurons. <i>In vitro</i>, treatment of microglia with aggregated α-syn leads to activation of antigen processing and presentation of antigen sufficient to drive CD4 T-cell proliferation and to trigger cytokine release. These results indicate a central role for microglial MHCII in the activation of both the innate and adaptive immune responses to α-syn in PD and suggest that the MHCII signaling complex may be a target of neuroprotective therapies for the disease.