In sera from patients with SLE, significantly more samples had detectable BLyS (67%; P < 0.0001) and APRIL (38%; P < 0.0002) levels compared with the healthy donor cohort (18% (BLyS) and 3% (APRIL)) (Figure 6a and Table 1). This evidence concerns the gene TNFSF13B and systemic lupus erythematosus.