[Pregnancy, acquired immunity and parasitic diseases: main mechanisms associated to resistance or susceptibility].

During pregnancy in mammals, the endocrine system plays a protagonic role, characterized by variation of different hormonal serum levels, such as estradiol, progesterone and some gonadotrophic hormones. Furthermore, the immunological system also participates during pregnancy, self-regulation for to avoid not rejecting the fetus. The characteristic immunity during the pregnancy is the humoral type: which is characterized by an increase in the levels of the Th-2 type cytokines IL-4, IL-6, IL-10, concomitant to a diminution in the levels of IL-2, INF-gamma and TNF-alpha The type of immunological response present during the pregnancy is mainly regulated by mechanisms associated to sexual hormones. This particular immunological response during the pregnancy, has individual importance if an infectious disease appears, since, depending on the parasite, a susceptibility or a resistance to the infection can exist. The proposed mechanisms to explain this resistance or susceptibility can be one of the following: (1) the hormones are influencing the immunological system of the host (by means of specific nuclear receptors); (2) the hormones acting directly on the parasite, preventing or promoting their reproduction and (3) a combination of both. These mechanisms support the idea of a complex immunoendocrine network (mediated by hormonal receptors, citokynes, antibodies) in host and parasite, interacting in a bidirectional way. The final outcome of this interaction is the death or survival of the host, or the parasite. In this review, we evaluate the information about the more frequent parasitic infections during pregnancy, and discuss the implied molecular mechanisms that affects the establishment, growth, reproduction or elimination of the parasite.