TNFRSF9 and infection: Therefore, we examined the possible roles of 4-1BB signaling in the placenta using agonistic anti-4-1BB mAb, blocking anti-4-1BB ligand mAb, and 4-1BB-deficient mice, and found that 4-1BB triggering resulted in rejection of semi-allogeneic fetuses, but was required to protect the pregnant mice from infections.