HLA-DRB1 and multiple sclerosis: Consequently, to further refine the nature of the secondary MHC association identified in our screening experiment, we typed the five classical HLA loci (HLA-A, -B, -C, -DRB1, and -DQB1) in an additional 721 sporadic UK multiple sclerosis patients and established UK control data from a cohort of 3,660 individuals (see Subjects and Methods).