Immunoendocrine mechanisms associated with resistance or susceptibility to parasitic diseases during pregnancy.

During pregnancy, the mammalian endocrine system plays a leading role in maintaining the fetus, characterized by an increase in the level of hormones such as progesterone, oestradiol and some gonadotropic hormones. The immune system participates during pregnancy by self-regulating to prevent fetus rejection. The distinctive type of immunity during gestation is characterized by an increase in levels of Th2 type cytokines IL-4, IL-6 and IL-10, concomitant with a decrease in IL-2, INF-gamma and TNF-alpha levels. Along pregnancy, sex steroids and factors associated with them regulate the immune response. In this way, endocrine and immunologic factors have an impact on the pregnant female's susceptibility or resistance to parasitic diseases. There are three main mechanisms proposed to explain this susceptibility or resistance: (1) sex steroids influence the host's immune system; (2) hormones acting directly on the parasites inhibit or promote their reproduction, or (3) the two effects can occur simultaneously within a network of immuno-endocrine host-parasite interactions, mediated by hormones, cytokines, antibodies and other factors interacting directly and bidirectionally. The present work reviews recent literature concerning the most frequent parasitic infections during pregnancy and discusses the mechanisms implied in the establishment, growth, reproduction or elimination of the parasite.