Vascular-associated lymphoid tissue (VALT) involvement in aortic aneurysm

Vascular-associated lymphoid tissue (VALT) consisting of accumulations of i mmunocompetent and antigen presenting cells has recently been recognised in the arterial wall. In this study, we investigated the involvement of VALT in immune responses in abdominal aortic aneurysms (AAAs). Tissue samples we re collected during operations from 31 patients with atherosclerotic infrar enal abdominal aortic aneurysms ranging in diameters from 5 to 8 cm. The sp ecimens were immediately frozen and examined using single and double immuno histochemical staining. T-cell subpopulations, B-cells, dendritic cells and macrophages were identified using cell type specific antibodies. Cell cont acts were examined by electron microscopy. Most inflammatory infiltrates we re found in the adventitia. T-cells were the predominant cell type in a maj ority of inflammatory infiltrates but in seventeen cases, typical lymphoid follicles with B-cells forming germinative centres were also observed. In e ight cases, the lymphoid follicles aggregated in lymph node-like structures . Dendritic cells were present within all inflammatory infiltrates and cont acted lymphocytes. The present observations show that in aortic aneurysm, V ALT is involved in immune responses and its activation mostly occurs in the adventitia. The formation of lymphoid follicles and lymph node-like struct ures in the adventitia suggests that VALT might locally serve the entire co mplex of both cellular and humoral immune responses in the aneurysmal wall. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.