LAUSR

Objective: Immunoglobulin (Ig) G4‐related aortic aneurysms (IgG4‐AAs) are a special aortic aneurysm among IgG4‐related diseases (IgG4‐RDs), which are inflammatory and fibrous conditions characterized by tumorous swelling of affected organs and high serum IgG4 concentrations. Recently, IgG4‐RD pathogenesis was shown to be associated with T‐helper‐2 (Th2) and regulatory T (Treg) dominant cytokine production, such as interleukin (IL)‐4, IL‐10, and IL‐13. IL‐6 is a key proinflammatory cytokine contributing to lymphocyte and plasmacyte maturation and to atherosclerosis and aneurysm development. We serologically and histopathologically evaluated the cytokine profile in IgG4‐AA patients. Methods: Patients with IgG4‐AAs (n = 10), non‐IgG4‐related inflammatory abdominal aortic aneurysms (non‐IgG4‐AAAs; n = 5), atherosclerotic AAAs (aAAAs; n = 10), and normal aortas without dilatation (n = 10) were examined for serum IL‐10, IL‐13, and IL‐6 levels. Resected aortic tissues were evaluated for cluster of differentiation (CD) 34 (in the endothelial cells and mesenchymal cells) and CD163 (by macrophages) expression using immunohistochemistry and in situ hybridization. Results: Serum IL‐10 levels were rather higher in IgG4‐AA patients (median, 1.3 pg/mL) than in non‐IgG4‐AAA and aAAA patients and in patients with normal aortas. Elevated serum IL‐13 levels relative to standard values were detected in two IgG4‐AA patients but not in the other groups. Cells immunopositive for IL‐10 and IL‐13 were more frequent in IgG4‐AAs and significantly correlated with serum IgG4 levels. Serum IL‐6 levels (median, 78.5 pg/mL) were also significantly higher in IgG4‐AA patients than in non‐IgG4‐AAA and aAAA patients and control patients with normal aortas (P = .01, P = .001, and P = .004, respectively). They positively correlated with serum IgG4 levels and adventitial thickness, but other cytokines did not. The number of IL‐6‐immunopositive cells in the adventitia was significantly higher in IgG4‐AA patients (median, 17.8/high‐power field) than in aAAA patients or patients with normal aortas (P =.001 and P = .002, respectively). In situ hybridization confirmed frequent IL‐6 messenger (m)RNA expression in the endothelium, mesenchymal cells, and histiocytes in IgG4‐AA adventitia. In the same cells of IgG4‐AAs, coexpression of IL‐6 and CD34 mRNA or CD163 mRNA was detected. Conclusions: The cytokine profiles of IgG4‐AA patients had two characteristics: local IL‐10 and IL‐13 upregulation in IgG4‐AAs was related to Th2 and Treg‐predominant cytokine balance, similar to other IgG4‐RDs, and IL‐6 upregulation in the adventitia was characterized by activated immune reactions in IgG4‐AA patients. IL‐6 synthesis, through contributions of mesenchymal cells and macrophages in the adventitia, is strongly involved in IgG4‐AA pathogenesis or progression, or both. Clinical Relevance: Interleukin (IL) 10 and IL‐13 upregulation in the aortic adventitia reflected T‐helper‐2 and regulatory T immune reactions in immunoglobulin (Ig) G4‐related aortic aneurysms (IgG4‐AAs) similar to other IgG4‐related diseases. Furthermore, IgG4‐AA was characterized by IL‐6 upregulation. In IgG4‐AA, serum IL‐6 correlated with serum IgG4 and adventitial thickness. Multiple cell populations, including the endothelium, mesenchymal cells, and macrophages in the adventitia, additionally contributed to the hyper‐IL‐6 syndrome in IgG4‐AA. Local IL‐6 synthesis in IgG4‐AA adventitia may play a role in disease pathogenesis and progression. Serum IL‐6 would be a useful biomarker for disease activity, and an IL‐6 inhibitor may serve as a new effective therapy for IgG4‐AA.