CD200 and Huntington disease: Next we determined CD200 (Fig 4C) and CD200R1 (Fig 4D) mRNA levels in peripheral blood comparing wild-type and R6/1 mice at pre-symptomatic (8 weeks; wt = 5; R6/1 = 5), prodromal (12 weeks; wt = 6; R6/1 = 6) and at manifest (25 weeks; wt = 12; R6/1 = 18) stages of HD pathogenesis.