Morphological and immunohistochemical comparison of intrapancreatic nerves between chronic pancreatitis and type 1 autoimmune pancreatitis.

OBJECTIVES: The abdominal pain associated with chronic pancreatitis (CP) may be related to the increased number and size of intrapancreatic nerves. On the other hand, patients with type 1 autoimmune pancreatitis (AIP) rarely suffer from the pain syndrome, and there are no previous studies concerning the histopathological findings of intrapancreatic nerves in patients with type 1 AIP. The current study is aimed at investigating the differences in the histopathological and immunohistochemical findings of intrapancreatic nerves in patients with CP and type 1 AIP.

METHODS: Neuroanatomical differences between CP and type 1 AIP were assessed by immunostaining with a pan-neuronal marker, protein gene product 9.5 (PGP9.5). The number (neural density) and area (neural hypertrophy) of PGP9.5-immunopositive nerves were quantitatively analyzed. Furthermore, the expression of nerve growth factor (NGF), and a high affinity receptor for NGF, tyrosine kinase receptor A (TrkA), was assessed by immunohistochemistry.

RESULTS: Both neural density and hypertrophy were significantly greater in pancreatic tissue samples from patients with CP than those with normal pancreas or type 1 AIP. NGF expression was stronger in type 1 AIP than in CP, whereas TrkA expression in type 1 AIP was poorer than in CP.

CONCLUSIONS: Although CP and type 1 AIP are both characterized by the presence of sustained pancreatic inflammation, they are different in terms of the density and hypertrophy of intrapancreatic nerve fibers. It is possible that this may be related to the difference in the activity of the NGF/TrkA-pathway between the two types of pancreatitis.