[Inhibitory Effect of CCL20 on CD4+ CD25+ regulatory T cell development in mouse thymus]

The aim of this study was to investigate the roles of chemokine CCL20 in development of CD4(+)CD25(+) thymocytes by means of fetal thymus organ culture. Fetal mouse thymus lobes were removed at the fetus age of 14.5 days and cultured in complete RPMI 1640 with 20% FBS in vitro. Phenotypes of the thymocytes were analyzed by FACS and the number of cells per lobe was counted. The results revealed that from day 14.5 to day 19, the absolute and relative numbers of the CD4(+)CD25(+) thymocytes varied similarly as their development as in vitro culture at 6 days. Data showed that during the 6 days in vitro culture the CD4(+)CD25(+) cell percentage out of CD4(+) cells was 58.29%, 12.14%, 6.08%, 17.78%, 9.06%, 4.04% and the CD4(+)CD25(+) cell percentage out of CD25(+) cells was 3.75%, 10.81%, 17.20%, 51.93%, 61.64%, 80.06%. All these data indicated similar characters to their development in vivo. Moreover, at interference with CCL20, the percentage of CD4(+)CD25(+) T cells in thymocytes significantly decreased at the 3 and 6 days from 3.24+/-0.18 and 3.96+/-0.24 to 1.27+/-0.11 (p<0.001) and 1.76+/-0.22 (p<0.001) respectively. It is concluded that the development of CD4(+)CD25(+) thymocytes is similar both in vitro and in vivo, interfering with CCL20 significantly downregulate the expression of CD4(+)CD25(+) T cells. The above data may help to understand the development of naturally arising CD4(+)CD25(+) regulatory T cells.