The size of endogenous APRIL protein isolated from sera of an atacicept-treated healthy subject or a SLE patient and detected by Western blot was 19 kDa before, and 16 kDa after treatment with peptide N-glycanase F, in close agreement with the presence of one consensus sequence for N-glycosylation and a predicted molecular weight of 16.4 kDa for the naked sequence of soluble mature APRIL (Figure 5E). Here, TNFSF13 is linked to systemic lupus erythematosus.