New insights in toxoplasmosis immunology during pregnancy. Perspective for vaccine prevention.

Toxoplasma gondii is one of the few pathogens that can cross the placenta. Frequency and severity of transmission vary with gestational age. While acquired toxoplasmosis is already well explored, the control of maternal-foetal transmission of the parasite remains almost unknown. This is partly due to inherent inadequacies of animal models. This review summarises the studies which have been undertaken and shows that the mouse is a valuable model despite obvious differences to the human case. The paramount role of the cellular immune response during primary infection has been consistently shown. Surprisingly, IFN-g has a dual role in this process. While its beneficial effects in the control of toxoplasmosis are well known, it also seems to have transmission-enhancing effects within the placenta and can also directly harm the developing foetus. This shows the importance of designing vaccines which protects both mother and foetus. Therefore, it is useful to study the mechanisms of natural resistance against transmission during a secondary infection. In this setting, the process is more complicated, involving cellular, but also humoral components of the immune system. In summary, even if the whole process is far from being elucidated, important insights have been gained so far which will help us to undertake rational vaccine research.