BTLA and systemic lupus erythematosus: Accordingly, when BTLA expression was analyzed on gated DN subsets, we confirmed that the lowest BTLA expression was observed on DN3 B cells (Figure 5D,E; p < 0.0001), although DN2 B cells express lower levels of BTLA than DN1 B cells (p < 0.05) in SLE patients but also in HCs (Figure S4).