CD28 and multiple system atrophy: The ration of Th/total T cells, the ratio of CD4+/CD8+ T cells, natural killer cells, CD28 expression on both CD4+ T cells and CD8+ T cells were higher in the MSA group (p < 0.05), but Tc and active marker (HLA-DR) expression on total T cells was lower (p < 0.05) (Table 4).