HO-1 modulates directly survival and maturation of trophoblast cells and promotes the fetal tolerance (reviewed by Schumacher and Zenclussen, 2015); however, the mechanisms that induce immunological tolerance can increase the susceptibility to infections caused by several types of pathogens, such as Toxoplasma gondii, which infects trophoblast cells and may be vertically transmitted to the embryo/fetus (reviewed by Arora et al., 2017). The gene discussed is HMOX1; the disease is infection.