T(H)2 predominant immune responses prevail in human abdominal aortic aneurysm

Abstract

T lymphocytes localize within lesions of two diametrically opposed expressions of atherosclerosis: stenosis-producing plaques and ectasia-producing abdominal aortic aneurysm (AAA). T(H)1 immune responses appear to predominate in human stenotic lesions. However, little information exists regarding the nature of the T-cell infiltrate in AAAs. We demonstrate here that AAAs predominantly express T(H)2-associated cytokines and correspondingly lack mediators associated with the T(H)1 response as determined by Western blot and immunohistochemical analysis. In particular, aneurysmal tissue expressed interleukin (IL)-4, IL-5, and IL-10, cytokines not or only faintly detected in nondiseased tissue or stenotic atheroma. In contrast, AAAs contained low levels of the T(H)1 characteristic cytokines IL-2 and IL-15, which are amply expressed in stenotic lesions. Notably, stenotic lesions, but not AAAs, contained mature forms of the interferon-gamma-inducing cytokines IL-12 and IL-18 as well as the IL-18-processing enzyme caspase-1. Moreover, aneurysmal tissue lacked the receptor for interferon-gamma, although both types of lesions contained this T(H)1-promoting cytokine. These findings suggest that the functional repertoire of T cells differs in stenotic and aneurysmal lesions, and provide a novel framework for understanding the mechanisms of these diametrically opposite expressions of atherosclerosis.

Figure 1.

Human AAAs contain T_H2-associated cytokines. Protein extracts (50 μg/lane) of nondiseased carotids (Normal), atheromatous carotids, and AAAs were applied to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subsequent Western blot analysis using either a mouse anti-human IL-2, IL-4, IL-5, IL-10, IL-15, or CD40L antibody. The positions of the molecular weight markers are indicated on the left. Analysis of tissue extracts obtained from seven nonatherosclerotic, eight atherosclerotic, and eight AAA surgical specimens from different individuals showed similar results.

Figure 2.

Human AAAs express the characteristic T_H2 cytokines IL-4 and IL-10. Serial cryostat sections of frozen specimens of human nondiseased carotids (Normal), carotid atheroma, or AAA were stained with either mouse anti-human IL-4 or IL-10 antibody. The asterisks indicate the lumen of the vessel. The inserts show higher magnifications (×400) of the T cell/macrophage-enriched area. Analysis of tissue obtained from seven nonatherosclerotic, eight atherosclerotic, and eight AAA surgical specimens from different individuals showed similar results.

Figure 3.

The T_H2 cytokine IL-4 colocalizes with immunocompetent cells. Serial cryostat sections of frozen specimens of human AAAs were applied to immunofluorescence double labeling using anti-human IL-4 (left; red) as well as anti-human CD3 (top right; T lymphocytes, green), or CD68 (bottom right; macrophages, green) antibody. Analysis of three AAA surgical specimens from different individuals showed similar results.

Figure 4.

Expression of IFN-γ-associated mediators is attenuated in human AAAs. Protein extracts (50 μg/lane) of nondiseased arterial tissue (normal), atherosclerotic lesions, and AAA (specimens obtained from three different donors are shown) were applied to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subsequent Western blot analysis using either an anti-human IL-12_p40, IL-18, IL-18 receptor α (IL-18Rα), caspase-1_p20, IFN-γ, or IFN-γ receptor-α (IFN-γRα) antibody. The positions of the molecular weight markers are indicated on the left. Analysis of extracts of a total of seven nonatherosclerotic, eight atherosclerotic, and eight AAA specimens from different individuals showed similar results.

Figure 5.

Expression of receptors for the T_H1 cytokines IL-18 and IFN-γ is diminished in human AAA. Serial cryostat sections of frozen specimens of nondiseased human arteries (Normal), carotid atheroma, or AAA were stained with antibodies recognizing either the human IL-18 receptor-α (IL-18Rα) or IFN-γ receptor-α (IFN-γRα). The asterisks indicate the lumen of the vessel. Analysis of tissues obtained from seven nonatherosclerotic, eight atherosclerotic, and eight AAA specimens from different individuals yielded similar results.