Cd4+cd25+ Regulatory T Cells Inhibite Macrophage-derived Foam Cells Formation By Down-regulating Scavenger Receptor Expression

Objective: CD4+CD25+ regulatory T(Treg) cells exert an suppressive activity on atherosclerosis but the underlying mechanism remains unclear. Here, we investigated whether and how Treg affect macrophages foam-cell formation, and thereby investigated the mechanism of Treg in the development of atherosclerosis.Methods:Treg were isolated from lymphocyte suspensions by magnetic cell sorting-column and analyzed by flow cytometry. Macrophages were cultured alone, with CD4+CD25+Treg, or CD4+CD25- T cells in the presence of ox-LDL for 48 hours to transform macrophages into foam cells. Oil red O staining and cellular lipid measurement 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 Treg-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(Fig. 1A). After treatment with Treg, 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 Treg was obtained when extracted oil red O and measured by a spectrophotometer.Cholesteryl ester accumulation also used to quantify foam cell formation. Compared with untreated (no T) and CD4+CD25-Treg-treated macrophage cells (CD25-), the lipids accumulation in CD4+CD25+Treg-treated macrophage foam cells (CD25+) was significantly reduced. Total cellular cholesterol and cellular cholesteryl ester was siginificantly reduced in CD25+ cultures relative to no T(TC: 58.5±7.0 vs 159.48±16.38, p<0.01; CE: 26.68±8.88 vs 102.54±16.67, p<0.001) or CD25- (TC: 58.5±7.0 vs 150.55±25.11, p<0.01; CE: 26.68±8.88 vs 96.90±11.95, p<0.001) cultures.Moreover, PCR and western blot analysis showed that the expression of both CD36 and SRA in Treg-treated macrophage foam cells was significantly down-regulated.Conclusion: Results collectively suggest that CD4+CD25+Treg cells may inhibit macrophage foam-cell formation, which is largely attributed to a downregulated expression in scavenger receptor in Treg-treated macrophage foam cells.