Regulatory B10 cells restore pregnancy tolerance in a mouse model.

During mammalian pregnancy, the immune system defies a double challenge: to tolerate the foreign growing fetus and to fight off infections that could affect both mother and fetus. Minimal disturbances to the fine equilibrium between immune activation and tolerance would compromise fetal survival. Here, we show that regulatory B10 cells are important for pregnancy tolerance in mice. The frequency of these cells increases during normal murine pregnancies, while mice presenting spontaneous abortion do not show elevated levels of regulatory B10 cells. When B10 cells are transferred to the abortion-prone mice, dendritic cells are kept in an immature state, and regulatory T cells increase, thus avoiding immunological rejection of the fetuses. In vitro, we could identify IL-10 secreted by B10 cells as the main mediator of these salutary effects. Our data add an important piece of information to the complex immune crosstalk during pregnancy. This study opens novel lines of work to better understand how to help women who have trouble in maintaining a pregnancy.