IT’S an enduring biological mystery – how a fetus survives in the uterus without being attacked by the mother’s immune system. Now it seems that in mice at least, a cellular “reception committee” gathers to welcome and guard each potential fetus that might be created during the menstrual cycle. The finding could reveal new ways of combating miscarriage in women.
Alexander Betz and Marinos Kallikourdis of the Laboratory of Molecular Biology in Cambridge, UK, discovered the process by exploring links between certain chemical shifts and menstrual cycles in mice. They knew the wombs of pregnant mice are especially rich in regulatory T-cells (Treg cells), which dampen the activity of other immune cells, and women who miscarry often have lower numbers of these cells. They also knew that chemical signalling molecules called chemokines that attract them to the uterus shift in concentration, apparently at random. “We wondered if the chemokine swings were controlled by hormones in the menstrual cycle,” says Betz. So in female mice they monitored concentrations of the chemokines and locations of the Treg cells through at least three cycles.
They found that concentrations of Treg cells in the womb rise and fall in tandem with the chemokines that summon them there (PLoS ONE, DOI: 10.1371/journal.pone.0000382). As the mouse’s fertile phase approaches, Treg cells gather in the uterus lining. If no pregnancy occurs, the cells disperse, only to regroup again at the same time and place in the next cycle.
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If a pregnancy does occur, a subset of Treg cells that has already encountered the alien male material in the embryo takes over and protects the fetus against rejection.
“If a pregnancy does occur, a subset of regulatory T-cells takes over and prevents the fetus from being rejected”
“This paper very carefully shows that Treg cells become enriched at the time the mouse is receptive to breeding,” says Anne Croy, a fertility researcher at Queen’s University in Kingston, Ontario.
