T and B lymphocytes play a minor role in atherosclerotic plaque formation in the apolipoprotein E-deficient mouse

Abstract

Cellular and humoral immunity have been implicated in the pathogenesis of atherosclerosis. To determine whether an intact immune system is necessary for the formation of atherosclerotic lesions, we have generated immunodeficient mice with hypercholesterolemia and atherosclerosis by crossbreeding the apolipoprotein E (apoE)-deficient mouse with the recombinase activating gene 1 (Rag-1) knockout mouse. Chow-fed immunodeficient mice with targeted disruption in both apoE and Rag-1 (E0/R0) had a 2-fold decrement in aortic root lesion size at 16 weeks of age, compared with immunocompetent littermates, which were heterozygotes at the Rag-1 locus (E0/R1). Nearly all atherosclerotic lesions from chow-fed animals were limited to raised foam cell fatty streaks. In contrast, when a second group of animals was fed a high-fat Western-type diet to accelerate lesion development, there were no differences in either aortic root lesion size or the percent of the total aorta occupied by lesions. Fibrous plaques with well-defined caps and necrotic cores were detected in both Western diet-fed E0/R0 and E0/R1 animals. We conclude that T and B lymphocytes play only a minor role in the rate of forming foam cell lesions, and they are not necessary for the formation of fibroproliferative plaques.

Figure 1

Aortic root and arch lesions from 16-week-old Western diet-fed mice. (Left) apoE-deficient, Rag-1 heterozygote mouse lesions (E0/R1). (Right) apoE-deficient, Rag-1-deficient mouse lesions (E0/R0). (A and B) Oil red O staining for lipid in aortic root lesions (4× objective). (C and D) Oil red O staining for lipid in aortic root lesions (20× objective) reveals fibroproliferative lesions with fibrous caps and cholesterol clefts. (E and F) α-Actin antibody staining (dark magenta) in aortic arch fibroproliferative lesions demonstrates smooth muscle cells in the fibrous cap (20× objective). (G and H) Macrophage antibody staining (red-brown) in aortic arch lesions with necrotic cores (20× objective).

Figure 2

Aortic arch lesions from 16-week-old Western diet-fed apoE-deficient, Rag-1 heterozygote mice. (A) Foam cell lesion stained for CD4⁺ T lymphocytes (red; 40× objective). (B) Macrophage antibody staining (red) of the same lesion as in A. (C) Fibrous lesion stained with CD4⁺ antibody demonstrates subendothelial T lymphocytes in a fibrous plaque (20× objective). (D) Macrophage antibody staining of the same lesion as in C demonstrates patchy macrophage staining and the presence of a necrotic core.