The role of interleukin-4 and interleukin-12 in the progression of atherosclerosis in apolipoprotein E-deficient mice

Abstract

Accumulation of T cells and macrophages in atherosclerotic plaques and the formation of antibodies directed against plaque proteins suggests that adaptive immunity contributes to the development of atherosclerosis. The contribution of Th1 and Th2 helper cell subsets to atherogenesis was studied in a murine model by interbreeding apolipoprotein E-deficient (apoE(-/-)) mice with mice deficient in key cytokines that drive either Th1 responses [interleukin (IL)-12] or Th2 responses (IL-4). Compared to apoE(-/-) mice, apoE(-/-)/IL-12(-/-) mice had a 52% reduction in plaque area in the aortic root at 30 weeks of age (P < 0.001). ApoE(-/-)/IL-4(-/-) mice had a 27% reduction in plaque area compared to apoE(-/-) mice (P < 0.05) at 30 weeks of age, but their plaques were significantly larger than in apoE(-/-)/IL-12(-/-) mice at this stage (P < 0.05). By 45 weeks of age, there were no significant differences in lesion sizes in the aortic root between the strains, however apoE(-/-)/IL-4(-/-) mice showed a 58% and 64% decrease in disease in their aortic arch compared to apoE(-/-) (P < 0.05) and apoE(-/-)/IL-12(-/-) (P < 0.05) mice, respectively, and a 78% decrease in thoracic lesions compared to apoE(-/-)/IL-12(-/-) (P < 0.05). This suggests that both Th1 and Th2 cytokines play roles throughout the development of atherosclerosis in various vascular sites in apoE(-/-) mice.

Figure 1.

Effect of IL-12 and IL-4 deficiency on plaque area in the aortic root of apoE^−/− mice. Small quantifiable lesions were detectable in all three groups at 15 weeks. Maximal increase in the size of lesions occurred between 15 and 30 weeks. Lesions in IL-4-deficient apoE^−/− mice were significantly smaller than in apoE^−/− at this time. Lesions in IL-12-deficient apoE^−/− mice were significantly smaller than both IL-4-deficient apoE^−/− mice and apoE^−/− mice. Lesion area in IL-12-deficient apoE^−/− mice increased significantly between 30 and 45 weeks. Numbers of mice in each group are shown in parentheses. *, P < 0.001 versus apoE^−/−; **, P < 0.05 versus apoE^−/−/IL-12^−/− and apoE^−/−; ***, P = 0.0002 versus 30-week apoE^−/−/IL-12^−/−.

Figure 2.

Effect of IL-12 and IL-4 deficiency on plaque area in the aortic arch and thoracic and abdominal aorta of apoE^−/− mice. At 30 weeks (A–C) there were no significant differences by analysis of variance in disease levels between the three strains in any of the vascular sites. At 45 weeks, apoE^−/−/IL-4^−/− mice had significantly less disease in the arch than both apoE^−/− and apoE^−/−/IL-12^−/− (D; *, P < 0.05) and significantly less than apoE^−/−/IL-12^−/− in the thoracic aorta (E; *, P < 0.05) (n = 4 to 7 in each group).

Figure 3.

Effect of IL-12 and IL-4 deficiency on mononuclear cell accumulation in lesions in apoE^−/− mice. Macrophage accumulation (A) was significantly less in IL-12-deficient apoE^−/− mice at 30 weeks (*, P = 0.026 versus apoE^−/−/IL-4^−/−). There were no significant differences in CD3, CD4, or CD8 T-cell accumulation (B and C) between any of the strains at either time point. Numbers of mice in each group are shown in parentheses.

Figure 4.

Total plasma IgG antibodies to oxLDL (A) in C57BL/6 mice, apoE^−/−, IL-4-deficient apoE^−/−, and IL-12-deficient apoE^−/−. Plasma from six animals was evaluated in each group at each time point. *, P < 0.05 versus apoE^−/−; **, P < 0.01 versus apoE^−/−, apoE^−/−/IL-4^−/−, and apoE^−/−/IL-12^−/−; ***, P < 0.05 versus apoE^−/−/IL-4^−/−; ^#, P < 0.05 versus apoE^−/−/IL-12^−/−. Plasma anti-oxLDL IgG isotypes (B–D) in C57BL/6 mice, apoE^−/−, IL-4-deficient apoE^−/−, and IL-12-deficient apoE^−/−. Plasma from four to eight animals was evaluated in each group at each time point.