The association of the high-risk genotype with altered MHC-II expression was revealed by: (1) increased surface protein expression of HLA-DR in monocytes; (2) greater inducibility of HLA-DQ surface protein expression in monocytes in response to IFN-γ; (3) increased mRNA expression of HLA-DRA, -DRB1, and -DQB1 genes; and (4) greater inducibility of mRNA expression in PD patients’ monocytes after IFN-γ stimulation. The gene discussed is HLA-DRB1; the disease is Parkinson disease.