1.5　Serum Markers

Hamano et al.（2001）reported that serum IgG4 was useful to diagnose AIP with high sensitivity and specificity in 2001.In the latest nationwide epidemiological survey in Japan（Kanno et al.2015a），serum IgG4 was elevated in 739/855（86.4%）patients with a mean value of 533 mg/dL.Anti-nuclear antibodies were positive in 263/785（33.5%）patients，486/862（56.4%）patients had high levels of IgG，and rheumatoid factors were positive in 125/576（21.7%）patients.Although elevated IgG4 is characteristic of type 1 AIP，an elevation of IgG4 is also seen in 5%of the normal population and in 10%of pancreatic cancer patients（Sah and Chari 2011）.Therefore，IgG4 is not a specific diagnostic marker for definitive AIP，but，when combined with other features of AIP，it can be of great value to diagnose AIP.(https://www.daowen.com)

Other serum specific biomarkers of AIP，especially those predicting disease relapse，have not yet been identified.Candidate markers include microRNA（miRNA）（Ciesla et al.2011）.MiRNA is a small noncoding RNA，20-23 bases in length.MiRNA orchestrates multiple biological processes by targeting hundreds of target mRNAs through the 3'untranslated region sequences，resulting in reduced expression of the target genes（Farazi et al.2011）.MiRNAs also exist within serum protected by stable structures such as the microvesicles or exosomes（Kosaka et al.2010）.Based on these unique characteristics，serum miRNAs have potential as novel biomarkers.Hamada et al.（2015）reported that hsa-miR-150-5p and hsa-miR-30-3p were commonly up-regulated in the serum of AIP patients compared to the samples of controls，chronic pancreatitis，and pancreatic cancer.The pathological roles of the up-regulated miRNAs remain to be clarified.