Immunohistochemical study of autoimmune pancreatitis using anti-IgG4 antibody and patients' sera.

Aims: Autoimmune pancreatitis (AIP), characterized by raised serum IgG4 levels, is frequently complicated by disorders of extrapancreatic organs. The aim of the present study was to examine immunohistochemically which extrapancreatic organs are affected, and whether an autoantibody to such organs is present in the serum of AIP patients.
Methods: Various tissues/organs obtained from AIP patients were studied immunohistochemically with an anti-IgG4 antibody. To examine the presence of an autoantibody in the serum of AIP patients, sera were incubated with various normal organs/tissues extracted for other diseases, followed by detection with an anti-IgG4 antibody. Sera were also examined before and after glucocorticoid therapy.
Results: Marked infiltration of IgG4+ plasma cells was observed in the pancreas, liver, bile duct and salivary gland of many of the AIP patients examined. The normal epithelia of the pancreatic ducts, bile ducts, gallbladder and salivary gland ducts reacting with the patients' sera were detectable by the anti-IgG4 antibody. Following glucocorticoid therapy the IgG4 antibody from the patients' sera showed decreased reactivity with these tissues.
Conclusions: AIP may also affect extrapancreatic organs, the serum of AIP patients may contain an IgG4 autoantibody to various organs and glucocorticoid therapy may improve such disorders.