In humans, the role for the various

In humans, the role for the various regulatory subsets are unknown. Although CD4+CD25+ regulatory T cells are expanded in the peripheral blood and decidua of pregnant women (15), the physiologic role of these cells in pregnancy has not been characterized fully. In this study, we explored the possibility that trophoblasts could modulate the immune system through an interaction with CD8+ T cells. The specificity of trophoblast-activated CD8+ T cell for regulating T cell-dependent B cell responses and the efficiency at which these cells are able to suppress Ig secretion suggests that these cells may occupy a regulatory niche during pregnancy. Overall, CD8+ regulatory T cells may contribute to the complex immune regulation that must occur during pregnancy.