Immunoglobulin G4-Related Inflammatory Aortic Aneurysm

1.1 The concept of immunoglobulin G4-related sclerosing disease Immunoglobulin G4 (IgG4) is the rarest subclass of IgG, which is numbered 1 through 4 in the order of their discovery and serum concentration, and normally constitutes only 3 to 6% of the total IgG fraction (Oxelius, 2008). IgG4 antibody has unique structural and functional properties, and the production of IgG4 appears to be driven in part by T helper 2 (Th2) cytokines that mediate allergic responses and IgE production (Nirula et al., 2011). The presence of IgG4 autoantibody in bullous skin diseases and high serum IgG4 concentration in patients with atopic dermatitis, bronchial asthma and bullous skin diseases have indicated that IgG4 plays an important role in these diseases (Jones et al., 1988; Jarvis et al., 2007). However, little attention had been paid to IgG4, before Hamano et al. revealed that serum IgG4 concentration was markedly elevated in patients with sclerosing pancreatitis (also called autoimmune pancreatitis) in 2001 (Hamano et al., 2001). Moreover, the same group also reported that the lesions of sclerosing pancreatitis and retroperitoneal fibrosis had abundant infiltration of IgG4-positive plasma cells (Hamano et al., 2002). Since then, many extrapancreatic lesions that share the same histopathological and immunohistochemical features as autoimmune pancreatitis have been reported in various organs, and the distinct clinicopathological disease entity, termed “IgG4-related sclerosing disease”, was established, because irrespective of origin of the organ, these lesions show common clinicopathological features (Kamisawa & Okamoto, 2008; Cheuk & Chan, 2010).