[1404] Abundant Infiltration of Immunoglobulin G4 Positive Plasma Cells: Autoimmune Pancreatitis vs Pilonidal Sinus

Y Fukumura, M Takase, K Suda, H Abe, K Mitani, T Hayashi, T Yao. Juntendo University, Bunkyo-ku, Tokyo, Japan; Tokyo-West Tokushukai Hospital, Akishima, Tokyo, Japan

Background: Abundant IgG4-positive plasma cells (G4-P) infiltrate in autoimmune pancreatitis (AIP) and its related diseases (AIP-Ds), hence immune mechanism via regulatory T cells (Treg) has been proposed in these disease entities. In our daily practice, many G4-Ps are observed not only in AIP-Ds but also in some non-AIP-Ds such as gastric ulcer, radicular cyst, and pilonidal sinus (PS). The aim of this study was to compare the amount of G4-P, ratio of G4-P / IgG1-positive plasma cells (G1-P), and CD25-positive lymphocytes between AIP and PS, in order to see the possible contribution of Treg in these disease entities.
Design: The study group consisted of pancreas from 4 AIP and skins from 10 PS. Formalin-fixed, paraffin embedded sections were prepared from these lesions. Sections were stained with H&E and with the antibodies IgG4, IgG1, and CD25. The amount of G4-Ps were scored (-), (1+), (2+), or (3+) according to Kamisawa's criteria.
Results: All the 4 cases of AIP showed up to (2+); diffuse and, in particular, periductal / interlobular infiltration of G4-Ps with storiform fibrosis were seen in all cases. The G4-P / G1-P ratio was 40.5 % to 120.5%. CD25 positive cells were less than 1 / HPF. PS cases showed G4-P score, (-) in 4 cases (40%), (1+) in 3 cases (30%), and (2+) in 3 cases (30%). In all PS cases, G4-Ps infiltrate mostly in granulation layer around the sinus of the PS. G4-P / G1-P ratio was 10.5 % to 150 %. CD25 positive cells were less than 1 / HPF.
Conclusions: (a) This study indicates that some cases of PS can show abundant G4-P infiltration and high G4-P / G1-P ratio, similar value as AIP, suggesting that histological G4-P score and G4-P / G1-P ratio are not enough for identifying AIP / AIPDs in our daily practice. To see the accompanying storiform fibrosis or granulation reaction may be helpful for the differential diagnosis. (b) In this study, only a few CD25-positive cells were seen both in AIP / PS, suggesting little contribution of Treg in AIP / AIPDs as well as in PS, at least with local level. Since this result may conflict with some recently published paper, which show higher serological level of Treg in AIP, additional study may be needed to investigate the other downstream members of 'T-reg to G4-P pathway' in these diseases.
Category: Liver & Pancreas

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 223, Wednesday Morning