CD4~+ CD25~+ regulatory T cells inhibit macrophage-derived foam cells formation by down-regulating scavenger receptor expression

Abstract

Objective To investigate whether and how regulatory T cells(Tr) affect macrophages foam-cell formation, and thereby investigate the mechanism of Tr in the development of atherosclerosis. Methods Tr were isolated from lymphocyte suspensions by magnetic cell sorting-column and analyzed by flow cytometry. Macrophages were cultured alone, with CD4~+ CD25~+ T, or CD4~+ CD25~- T cells in the pres-ence of oxLDL for 48 h to transform macrophages into foam cells. Oil red O staining and cellular lipid meas-urement were used to identify macrophage foam cell formation. Semi-quantitative PCR, quantitative real-time PCR and Western blot analysis were carried out to explore the mechanism of Tr-mediated suppression on macrophages foam cell formation. Results Foam cell formation, as identified by oil red O staining, was readily apparent in cells treated with CD4~+ CD25~- T cells and without T cells. After treatment with Tr, a marked decrease(13.9% ± 5.6% ) in foam cell count was observed, compared with untreated cells(13.9% ±5.6% vs 52.9% ± 10.4%, P<0.001 ) or CD4~+ CD25~- T-treated cells(13.9% ± 5.6% vs 53. 1% ± 17.2%, P<0.001 ), 52.9% ± 10.4% and 53.1% ± 17.2%, respectively (P<0.001). The similar effect of Tr was obtained when extracted oil red O and measured by a spectrophotometer. Cholesteryl ester ac-cumulation also used to quantify foam cell formation. Compared with untreated (no T) and CD4~+ CD25~- Tr-treated macrophage cells (CD25~-), the lipids accumulation in CD4~+ CD25~+ Tr-treated macrophage foam cells(CD25~+) was significantly reduced. Total cellular cholesterol and cellular cholesteryl ester was siginifi-cantly reduced in CD25~+ cultures relative to no T[TC(total cholesterol): 57.46 ± 17.92 vs 159.48 ± 16.38, P<0.01 ; CE(esterified cholesterol): 26.68 ± 8.88 vs 102.54 ± 16.67, P<0.001] or CD25~- (TC: 58.50±7.00 vs 150.55±25.11, P<0.01; CE: 26.68±8.88 vs96.90 ± 11.95, P<0.001) cul-tures. Moreover, PCR and Western blot analysis showed that the expression of both CD36 and SRA in Tr-treated macrophage foam cells was significantly down-regulated. Conclusion Results collectively suggest that CD4~+ CD25~+ Tr cells may inhibit macrophage foam-cell formation, which is largely attributed to a down-regulated expression in scavenger receptor in Tr-treated macrophage foam cells. Key words: CD4~+ CD25~+ T cell; Macrophage foam cell; Atherosclerosis; Scavenger receptor