Prohibitin antibodies were found in 73.5% (n = 34) of patients with definite AIP, 53.3% (n = 15) with Mikulicz’s disease, 54.5% (n =11) with retroperitoneal fibrosis, and 89.7% (n = 29) with other probable IgG4-RD but in only 1.4% (n = 70) of healthy donors. The gene discussed is PHB1; the disease is IgG4-related retroperitoneal fibrosis.