Circulating IgG4+ Plasmablast Count as a Diagnostic Tool in Autoimmune Pancreatitis

BACKGROUND & AIMS: Type 1 autoimmune pancreatitis (AIP) is an IgG4-related disease whose diagnosis is challenging. The aim of this study was to investigate the diagnostic value of circulating total and IgG4þ plasmablasts in differentiating this condition from the other main pancreatic diseases. METHODS: Patients with type 1 AIP (n ¼ 19) were prospectively enrolled in a tertiary center together with patients suffering from type 2 or not otherwise specified (NOS) AIP (n ¼ 10), pancreatic adenocarcinoma (n ¼ 17), chronic pancreatitis (n ¼ 20), and intraductal papillary mucinous neoplasia or chronic asymptomatic pancreatic hyperenzymemia (n ¼ 21) as control groups. Flow cytometry was used to measure the total plasmablast and IgG4þ plasmablast number by gating peripheral blood CD45þCD19þCD38hiCD20-CD24-CD27þ and CD45þCD19þCD38hiCD20-CD24-CD27þIgG4þ cells, respectively. In patients with AIP, these cell populations were also evaluated after 1 month of therapy, after 2–4 months from the end of treatment, and after 1 year from the enrollment. The study was approved by the local ethics committee (protocol number: 59133, 30/11/2017). RESULTS: Total plasmablast quantification was capable of discriminating type 1 AIP from all the other pancreatic disorders with a sensitivity of 47% and a specificity of 81%, according to a cutoff of 4500 cells/mL (AUC ¼ 0.738), whereas IgG4þ plasmablast count distinguished type 1 AIP from all the other pancreatic disorders with a sensitivity of 80% and a specificity of 97% when applying a cutoff of 210 IgG4þ cells/mL (AUC ¼ 0.879). The basal IgG4þ plasmablast number was significantly higher (P ¼ .0001) in type 1 AIP than in type 2/NOS AIP, decreased after steroid therapy, and increased at disease relapse. CONCLUSION: IgG4þ plasmablast count represents a potentially useful biomarker to differentiate type 1 from type 2/NOS AIP and from other pancreatic diseases.