[Non-specific immune defenses present in pregnancy]

The state of pregnancy changes the immune system by allowing the trophoblast to go on developing without letting the mother's body be invaded by it, and by keeping intact immune defences against the usual assaults. The non specific immune system is the first bulwark against invaders. The elements of this system, which do not depend on immunological memory, are: the macrophage-monocyte system, Natural Killer cells (NK), the complement component and other bactericidal substances such as lysozyme, fibronectin and interferon. Pregnancy improves the working of the monocyte-macrophage system. In fact, the macrophages of th reticulo-endothelial system, which can be found in different strategic places in the body, phagocytose abnormal particles more intensely. The monocytes in the circulation are more aggressive in pregnancy. They are drawn to the feto-placental interface where they are activated by different lymphokines and cytokines which can be found in quantity at this site. The role of these local active monocytes is not limited only to phagocytosis because among the hundred substances that they can elaborate are some that will regulate trophoblastic proliferation. The activity of the Natural Killer cells that are circulating and which can control tumour cell growth and cells infected by viruses is lowered in pregnancy. The serum taken from pregnant women seems to have a substance that counters the maturation of the Natural Killer cell lines. The complement system of protein synthesis, which normally acts to lyse bacteria in the chemotaxis during opsonisation, is raised in pregnancy. At the feto-placental interface it does seem to activate this system but not elsewhere in the general circulation. Interferon, which is a molecule that normally activates NK cells, has been found at the feto-placental site, without seeming to have a particular role. Pregnancy changes the quantity and the distribution of other elements in the non specific immune system such as transferrin , fibronectin and beta-lysin.