DPP4 and granulomatosis with polyangiitis: Four out of five proteins selected during a preliminary screening, namely, insulin-like growth factor binding protein 2 (IGFBP-2), basigin (CD147), chitinase-3-like protein 1 (CHI3L1), and trefoil factor 3 (TFF-3), were elevated in the serum of patients with active GPA, whereas dipeptidyl peptidase-IV (DPP-IV) was significantly decreased.