Possible involvement of Toll-like receptor 7 in the development of type 1 autoimmune pancreatitis.

Background: High serum immunoglobulin G4 (IgG4) levels and IgG4-positive plasma cell infiltration are characteristic of type 1 autoimmune pancreatitis (AIP). It is unclear whether innate immunity is a cause of type 1 AIP; the possible involvement of microbial infection has been suggested in its pathogenesis. To clarify the pathogenesis of type 1 AIP, we investigated Toll-like receptors (TLRs) in type 1 AIP patients.
Methods: We studied nine cases of type 1 AIP with ten cases of alcoholic chronic pancreatitis (ACP) and three of the samples from non-tumorous lesion of neuroendocrine tumor (NET) as control subjects. We counted the number of TLR1-11-positive cells immunohistochemically stained with anti-TLR1-11 antibodies. To identify TLR-positive cells in pancreata from type 1 AIP patients, we used a double-immunofluorescence method and counted the numbers of identifiable CD68-, CD163-, CD123-, and CD20-positive cells.
Results: In type 1 AIP, TLR7 (8.815 ± 1.755), TLR8 (3.852 ± 1.489), and TLR10 (3.852 ± 0.921) were highly expressed. Only the ratio of TLR7 per monocyte was significantly higher in type 1 AIP (0.053 ± 0.012) than in ACP (0.007 ± 0.004; p < 0.01) and non-tumorous lesion of NET (0.000 ± 0.000; p < 0.01). In type 1 AIP, the CD163 to TLR7 ratio (0.789 ± 0.031) was significantly higher both than that of CD123 to TLR7 ratio (0.034 ± 0.006; p < 0.001) and CD20 to TLR7 ratio (0.029 ± 0.010; p < 0.001).
Conclusions: TLR7 might be key pattern-recognition receptors involved in the development of type 1 AIP.