I have read some literature about the role of Kurloff's cells in guinea pigs. During the  gestation period, Kurloff's cells, which are peripheral WBC, migrate to placenta and become resident. It meant to protect the fetus from destruction by maternal antibody. I can't find literature that explains the mechanism briefly. What calls Kurloff's cells to go to placenta? Why are Kurloff's cells needed to protect the fetus, unlike in other mammals?

Thanks for response ^_^