CD4 and systemic lupus erythematosus: After being isolated from PBMCs of SLE or control mice, CD4 + T cells were suspended at 1 × 107 cells/mL in 100 μL cell staining buffer containing 10 μL FITC anti-Mouse CD4 (100405, Biolegend)/FITC anti-Mouse CD4 ISO (400605, Biolegend), and incubation was performed under dark conditions at room temperature for 20 min.