The cell surface expression of CTLA-4 in T cells was higher in HT patients than in the control group; after phytohemagglutinin (PHA) stimulation for 48 h, the number of CD4 T cells expressing CTLA-4 increased in both HT patients and controls, but CTLA-4 expressed on the cell surface increased only in HT patients (101). Here, CTLA4 is linked to hematocrit.