CD200 and Parkinson disease: Evidence of MRC dysfunction in PD emerged in the early 1980s following the intravenous injection of 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP) by drug abusers, producing the neurotoxin 1-methyl-4-phenylpyridinium (MPP+) via the monoamine oxidase-B (MAO-B) enzyme, which consequently induced Parkinson-like symptoms [72].