CTLA4 and systemic lupus erythematosus: After activation of PBMCs with IL-2, IL-7, and PHA for 48 h, the expression of CD4+ CTLA4+ in all lymphocytes showed significant differences between the control group (MFI = 11.39 ± 2.44) and severe SLE (MFI = 7.21 ± 0.50, p = 0.001) (Figure 6a).