Increased Expression of Activation-Induced Cytidine Deaminase in Sinus Mucosa from IgG4-Related Disease Patients with Comorbid Chronic Rhinosinusitis.

Objective: IgG4-related disease (IgG4-RD) is a systemic condition characterized by an elevated serum IgG4 level, localized infiltration of IgG4-positive plasma cells, and lesions in various organs. IgG4-RD also shows high rates of complication with allergic diseases and is often accompanied by elevated serum IgE levels. Reports in recent years have also shown high rates of complication with chronic rhinosinusitis (CRS) and its characteristic nasal manifestations. Accordingly, we speculate that there may be a distinct form of CRS that, as an IgG4-RD, differs from other CRS. Here, we investigated whether the elevated levels of factors that are thought to be important in the pathogenesis of IgG4-RD are also seen in the sinus mucosa of IgG4-RD-associated CRS patients.

Methods: Ethmoid sinus mucosa specimens from 9 IgG4-RD (6 Mikulicz disease and 3 Küttner's tumor) patients with elevated serum IgG4 and IgE and from 22 control CRS patients were examined immunohistochemically for Treg cytokines (IL-10 and TGF-β), activation-induced cytidine deaminase (AID), and immunocompetent cells. The 22 control CRS patients were divided into 3 subgroups based on the serological findings for IgG4 and IgE. Quantitative real-time PCR was performed to examine the expression of AID.

Results: The ethmoid sinus mucosa from patients with IgG4-RD-associated CRS showed, in comparison with the 3 CRS control subgroups, significantly elevated AID production. Their mucosa also showed significantly increased infiltration of CD-20-positive immunocompetent cells compared with the controls. On the other hand, immunohistochemical examination found no significant differences in the number of IL-10- or TGF-β-positive cells.

Conclusion: Ethmoid sinus mucosa from IgG4-RD-associated CRS patients showed clearly increased AID production, suggesting AID involvement in class-switching to IgG4 in those local sites. This implies the existence of a distinct form of CRS that is an IgG4-RD.