BTLA expression was found to be lower on DN memory B cells from SLE patients and interestingly, the frequency of this B cell population is higher in SLE patients than in HCs and particularly in active SLE patients (4.7% ± 0.3 in HCs vs. 8.7% ± 1.7 in patients with inactive SLE or with low disease activity, SLEDAI < 6; p < 0.01; and vs. 13.6% ± 2.1 in patients with mild to severe SLE, SLEDAI ≥ 6; p < 0.0001) (Figure 2A). This evidence concerns the gene BTLA and systemic lupus erythematosus.