Deposition of complement C3c, IgG4 and IgG at the basement membrane of pancreatic ducts and acini in autoimmune pancreatitis

Aims: Autoimmune pancreatitis(AIP) is a type of pancreatitis whose immunopathogenesis is still unknown. It has been reported that kidney biopsy specimens from patients diagnosed with both AIP and tubulointerstitial nephritis revealed deposits at tubular basement membranes (BMs) containing complement C3, IgG and also IgG4. Our aim was to investigate the deposition of complement and immunoglobulins in pancreatic tissue from AIP patients compared to non-AIP patients. Methods: On frozen pancreatic tissue from AIP and alcoholic chronic pancreatitis (ACP) patients, double immunofluorescencemicroscopy for C3c, IgG4 and IgG together with CK7, trypsin, collagen IV, CD31and CD79aas well as immunofluorescencemicroscopy for C1q, IgA and IgM were performed. Results: In AIP patients, complement C3c, IgG4 and IgG were deposited at the collagen IV-positive BM of pancreatic and bile ducts and of acini. In a minority of the ACP patients, weak C3c-positive BM deposits were detected, but no IgG4- or IgG-positive BM deposits were present in ACP. Conclusion: The deposition of C3c, IgG4 and IgG at the BM of small and medium-sized ducts and acini of the pancreas is characteristic of AIP. This suggests that immune complex-mediated destruction of ducts and acini may play a role in the pathogenesis of AIP.