T helper-cell phenotype regulates atherosclerosis in mice under conditions of mild hypercholesterolemia

Abstract

Background: T cells are implicated in atherosclerosis, but little is known about the genetic control or molecular pathways, especially under conditions of mild hypercholesterolemia.

Methods and results: BALB/c mice, making a CD4+ Th2 (IL-4+) cell response, express both MHC class II antigens (IA(d), IE(d)) and are atherosclerosis-resistant. C57Bl/6 mice produce a CD4+ Th1 (interferon [IFN]gamma+) response, express IA(b) but no IE, and are atherosclerosis-prone. To evaluate T helper-cell phenotype in fatty streak formation, wild-type C57Bl/6 mice (IA(b)+IE-) and transgenic mice, either AB(o), IA(b)-IE-; ABEalpha, IA-IE(k)+; or BL:TG:Ealpha, IA(b)+IE(k)+, were fed a high-cholesterol diet for 16 weeks and evaluated histomorphometrically for aortic lesions. Lesion size in AB(o), ABEalpha, and BL:TG:Ealpha strains was decreased by 54%, 79%, and 82%, respectively, compared with wild-type, correlating with decreased Th1 and increased Th2 expression and suggesting that T helper-cell phenotype is important in fatty lesion development. Decreasing Th1 cells by antibodies (alpha-CD4) or cytokines (IL-4) also caused >/=80% reductions in lesion size. Immunohistology revealed IFN-gamma, but not IL-4, colocalized with activated macrophages. Confirming these findings in a different mouse strain, BALB/c Stat 6 knockout mice (Th2 cell-deficient) developed aortic lesions comparable to C57Bl/6 mice on the same diet.

Conclusions: In mildly hypercholesterolemic C57Bl/6 mice, presence of IA(b) and absence of IE regulated CD4+ T helper-cell phenotype; fatty lesions were proportional to IFNgamma+ Th1 cells in both C57Bl/6 and BALB/c strains. IFN-gamma may participate through macrophage activation, whereas IL-4 may act to limit Th1-cell response.