Sex-Associated Hormones and Immunity to Protozoan Parasites

Abstract

Numerous epidemiological and clinical studies have noted differences in the incidence and severity of parasitic diseases between males and females. Although in some instances this may be due to gender-associated differences in behavior, there is overwhelming evidence that sex-associated hormones can also modulate immune responses and consequently directly influence the outcome of parasitic infection. Animal models of disease can often recreate the gender-dependent differences observed in humans, and the role of sex-associated hormones can be confirmed by experimentally altering their levels. Under normal circumstances, levels of sex hormones not only differ between males and females but vary according to age. Furthermore, not only are females of reproductive age subject to the regular hormonal cycles which control ovulation, they are also exposed to dramatically altered levels during pregnancy. It is thus not surprising that the severity of many diseases, including those caused by parasites, has been shown to be affected by one or more of these circumstances. In addition, infection with many pathogens has been shown to have an adverse influence on pregnancy. In this article we review the impact of sex-associated hormones on the immune system and the development and maintenance of immunity to the intracellular protozoan parasites Toxoplasma gondii, Plasmodium spp., and Leishmania spp

Occurrence and risk factors associated with infection by Toxoplasma gondii in goats in the State of Alagoas, Brazil

“…Under controlled conditions in the laboratory, a dichotomy in the susceptibility between males and females is evident, revealing that physiological differences between males and females, mainly hormonal, play an important role in determining susceptibility to parasitic infections 30 .…”

Sex Hormones and Immunity to Infection

“…As noted above, the prevalence and intensity of infectious diseases is generally higher in males than in females (Roberts et al 2001;Simon et al 2005;Zuk and McKean 1996). The interactions that exist between the endocrine and immune systems are important in considering why males and females differ in susceptibility to infectious agents.…”

“…Of course, this reflects differences in exposure as well as inherited differences in susceptibility to pathogens (Klein 2000(Klein , 2004Roberts et al 2001;Zuk and McKean 1996). Heightened susceptibility to infection is one of the leading explanations of the greater death rates among men than among women reported in several locations around the world.…”

“…The greater immunity among females creates a double-edge sword; it is beneficial as a defense against infectious diseases, but is detrimental in the increased occurrence of autoimmune diseases (Wizemann and Pardue 2001). Sexbased differences typically become apparent after puberty (Klein 2000;Roberts et al 2001) and several field and laboratory studies link sex differences in immune function with circulating steroid hormones (Klein 2000(Klein , 2004Roberts et al 2001;Zuk and McKean 1996). Sex hormones change profoundly during pregnancy where they must modulate the immune system to facilitate a successful pregnancy among viviparous animals (Roberts et al 1996).…”

A high corticosterone/DHEA-s ratio in young rats infected with Trypanosoma cruzi is associated with increased susceptibility

“…In contrast, adult animals inoculated with T. cruzi only showed a mild disease with extremely low parasitaemia values (Revelli et al 1987, Pascutti et al 2003. These age-related susceptibility differences might be explained by immune system maturity and endocrine influences as both play an integral role in biological defence mechanisms (Roberts et al 2001).…”