Immunogenetics of Parkinson's disease

Inflammation is a key feature of Parkinson’s disease (PD). In postmortem PD brains, microglial activation and enhanced major histocompatibility class II (MHCII) expression are seen concomitant to the accumulation of alpha-synuclein (α-synuclein) and loss of dopaminergic cells in the substantia nigra. Recent findings showed that α-synuclein epitopes can be presented and recognized by T-cells. PD is not a single disorder; rather, it encompasses a range of clinical, epidemiological, and genetic subtypes. Around 10% of the cases have a monogenic origin, and several of the disease-causing mutations are linked to inflammatory processes. The remaining 90% of the cases are complex, where environmental and genetic risk factors synergize to induce PD pathology. To date, 41 genetic loci have been identified in genome-wide association studies as associated with PD risk, and among these, two are within the HLA region, coding for immune genes including MHCII. Thus, genetic and immune findings indicate that the immune system has a role in the etiology of PD. Experimentally, inflammatory stimuli can cause selective nigral cell loss in preclinical models of PD, and MHCII is required to elicit α-synuclein-induced pathology in mice. In this chapter, we focus on immunogenetics, that is, the relation between genetic risk factors and immune processes in PD