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Functional characterization of T cells in abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) exhibit features of a chronic inflammatory disorder. The functional attributes of the T cells in AAA tissue are unclear, with little quantitative or functional data. Using a novel, non‐enzymatic method to isolate viable cells from AAA tissue, functional properties of AAA T cells were investigated for the first time. Composition and phenotype of AAA T cells was determined by flow cytometry and verified by immunohistochemistry. Tissue mononuclear cells (MNCs) were cultured in the presence of T‐cell mitogens, and cell cycle analysis and cytokine production assessed. Typical cell yield was 4·5 × 106 cells per gram of AAA tissue. The majority (58·1 ± 5·3%) of haematopoietic (CD45+) cells recovered were CD3+ T cells, B cells comprised 41·1 ± 5·7%, natural killer cells 7·3 ± 2·5%, and macrophages 2%. Freshly isolated T cells were in resting (G1) state, with 25% expressing the activation‐associated cell surface antigens major histocompatibility complex II and CD25. When stimulated in vitro, a significant proportion entered S and G2 phase of the cell cycle, up‐regulated CD25, and secreted tumour necrosis factor‐α, interferon‐γ, interleukin (IL)‐5 and IL‐6. Despite patient differences, the composition of the AAA inflammatory infiltrate was remarkably consistent, and when re‐stimulated ex‐vivo T cells produced a stereotypical cytokine response, consistent with the hypothesis that AAA T cells can promote tissue inflammation by secretion of proinflammatory cytokines, and in addition provide signals for B‐cell help.