We examined the global gene expression pattern of T cells regulated by progesterone to gain further insights into the regulatory mechanisms of progesterone. We found 325-347 cord blood T cell genes up or down-regulated by P4 in the presence or absence of exogenous TGFb1. Peripheral blood T cells were relatively unresponsive with only 30-70 genes regulated by P4. IL-6 receptor (IL-6R) expression was greatly down-regulated by progesterone in cord blood, but not PB, T cells. Overall, these differences in gene expression are consistent with the differential responses of cord blood and peripheral blood T cells to progesterone. To gain insights into the differences of progesterone and control dendritic cells, we performed a microarray study and found ~180 genes regulated by progesterone in dendritic cells. The gene expression information suggests that progesterone has the potential to alter dendritic cell responses to cytokines, chemokine production, and migration which in combination would control T cell differentiation.