TNFSF13B and anti-neutrophil cytoplasmic antibody-associated vasculitis: Increased expression of B-cell activation factor of the tumor necrosis factor family (BAFF) and a proliferation-inducing ligand (APRIL) expression, which have been observed not only in the active phase of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) but also in remission, may cause relapse by activating autoreactive B cells that produce ANCA.