Statistical analysis
All experiments were repeated three times with each group had 10 mice and data were expressed as mean ± standard error of mean(SEM). FLOWJO 7.6.1(Treestar) was used to analyze the flow cytometry data and GRAPHPAD PRISM 5.0(GraphPad Software Inc., San Diego, CA) was used to draw the graphs. Other statistical analyses were performed using SPSS 21.0(IBM Deutschland, Ehningen, Germany). The student’s t-test was used for comparisons between two groups. All tests were two-tailed. P<0.05 was considered statistically significant, represented by *(P<0.05), **(P<0.01), ***(P<0.001), and ****(P<0.0001).