Probes for CD34

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.