CTLA4 and systemic lupus erythematosus: In CD3+ CD4+ cells, the expression of CD3+ CTLA4+ also showed significant differences between the control (MFI = 19.16 ± 1.91) and mild SLE (MFI = 13.65 ± 3.95, p = 0.011), as well as between control and severe SLE (MFI = 15.2 ± 3.76, p = 0.006) (Figure 6b).