The percentages of BTLA on CD4+ T-cells were significantly decreased in active SLE patients as compared to healthy controls (86.4% ± 3.8% vs. 90.4% ± 3.9%, p = 0.02) and as compared to inactive SLE patients, respectively (86.4% ± 3.8% vs. 89.8% ± 3.6%, p = 0.03). Here, BTLA is linked to systemic lupus erythematosus.