CD40 and Huntington disease: Unlike no difference in the expression of costimulatory molecules, CD86 and CD40, between R6/2 Tg mice and WT littermates at pre-manifest stage HD (4-week-old), the expression levels of these molecules were significantly decreased in R6/2 Tg mice at late stage HD (12-week-old) compared to that in WT littermates (Figure 2C).