Type 2 autoimmune pancreatitis (
type 2 AIP) develops in isolation or sometimes in association with
ulcerative colitis. Its diagnosis requires the histologic confirmation of granulocytic epithelial lesions (
GELs) with no diagnostic
biomarker currently available. This study aimed to elucidate the tissue expression of
cytokines and their diagnostic value in this condition. In quantitative polymerase chain reaction for multiple
cytokines using tissue-derived
mRNA, the expression level of
interleukin (IL)-8 was markedly higher in
type 2 AIP than in
type 1 AIP (P<0.001). In immunostaining,
IL-8 expression was detected in the ductal/ductular epithelium (11/13; 85%) and infiltrating neutrophils or lymphocytes (12/12; 100%) in
type 2 AIP, but was almost entirely negative in
type 1 AIP (n=13; both, P<0.001). Although obstructive
pancreatitis adjacent to
pancreatic cancers (peritumoral
pancreatitis) exhibited
IL-8 expression in the epithelium (3/12; 25%) and inflammatory cells (10/12; 83%), expression levels were significantly lower than those in
type 2 AIP (P<0.001 and 0.020, respectively). The presence of either
GELs or IL-8-positive epithelium discriminated
type 2 AIP from
type 1 AIP or obstructive
pancreatitis with 92% sensitivity and 92% to 100% specificity. Furthermore, CD3/IL-8-coexpressing lymphocytes were almost restricted to
type 2 AIP. Interestingly, a similar pattern of
IL-8 expression was also observed in colonic biopsies of
ulcerative colitis. In conclusion, the overexpression of
IL-8 may underlie the development of
GELs in
type 2 AIP, and
IL-8 immunostaining or IL-8/CD3 double staining may become an ancillary method for its diagnosis. The similar expression pattern of
IL-8 in
ulcerative colitis also suggests a pathogenetic link between the 2 conditions.