Objective To investigate the mechanism of CD4⁺CD25⁺treg in atherosclerosis in ApoE-/- mice.

Methods 28 weeks-old male ApoE^−/− mice were randomly divided into two groups feeding high-fat diet (AH) or normal diet (AN). Ten C57BL/6J male mice feeding normal-diet (BN). After 12 weeks, the whole aorta from the root to crotch of iliac artery was separated and the whole blood were centrifugated to get the serum. Paraffin sections of aorta were stained with H&E and morphometric parameters were measured using Image Pro Plus 6.0 system. Immunohistochemical stain was performed to verify the expression of the Foxp3⁺ and CD25⁺ cells in atherosclerotic tissue (%). The ratio of CD4⁺CD25⁺/CD4⁺ in spleen was calculated by Flow Cytometry. The serum concentration of TGF-β1, IL-10 were detected by ELISA. SPSS13.0 was used to analyse the data. All values were expressed as Mean±SD. Independent-Samples T Test was applied to compare two samples of quantitative data after testing their normality. p<0.05 was considered statistically significant.

Results There were advanced atherosclerotic plaques in ApoE^−/− mice, but in C57BL/6J. The thickness of intima (μm), plaque area (μm²), plaque/lumen ratio in AN group were significantly higher than in BN group (12.24±1.34 vs 7.33±2.23, 600265.4±263876.25 vs 0, 15.93±5.45 vs 0, all p<0.01). So did in AH group than that in AN group (all p<0.05). The percentage of spleenic CD4⁺CD25⁺treg (%) and the serum concentration of TGF-β1, IL-10(pg/ml) in AN group were significantly decreased than in BN group (9.4±4.00 vs 13.8±3.97, 116.05±32.27 vs 191.27±95.27, 41.83±16.15 vs 61.84±23.05, all p<0.05). These in AH group significantly reduced than in AN group (5.8±1.51 vs 9.4±4.00, 83.97±33.45 vs 116.05±32.27, 27.50±11.54 vs 41.83±16.15, all p<0.05). There were no Foxp3⁺ and CD25⁺ cells in plaques-free intima in BN group. The expression of Foxp3, CD25⁺ cells were significantly decreased in AH group than in AN group (1.28±1.20 vs 3.04±1.92, 2.00±1.39 vs 3.98±1.67, all p<0.05).

Conclusions The spleenic CD4⁺CD25⁺treg and serum concentration of TGF-β1, IL-10 of mice were decreased and there were lower frequency of Foxp3⁺ and CD25⁺ cells in severe atherosclerotic plaques than in mild. It meant that CD4⁺CD25⁺treg may has anti-atherosclerotic role on atherosclerotic progression.