CD28 and hematocrit: Including HT and HC, age, sex, disease duration and CMV-seropositivity into a linear regression model, the absolute lymphocyte counts (R = 0.493; p < 0.01) and the CD28-negative T cell subpopulations (CD4+: R = 0.504; p < 0.01; CD8+: R = 0.469; p < 0.01) were only influenced by having HT.