Abstract
In many cases parasites display highly complex life cycles that include the penetration and permanence of the larva or adults within host organs, but even in those that only have one host, reciprocal, intricate interactions occur. Evidence indicates that steroid hormones have an influence on the development and course of parasitic infections. The host gender's susceptibility to infection, and the related differences in the immune response are good examples of the host-parasite interplay. However, the capacity of these organisms to synthesize their own steroidogenic hormones still has more questions than answers. It is now well-known that many parasites synthesize ecdysteroids, but limited information is available on sex steroid and corticosteroid synthesis. This review intends to summarize some of the existing information in the field. In most, but not all parasitosis the host's hormonal environment determines the susceptibility, the course, and severity of parasite infections. In most cases the infection disturbs the host environment, and activates immune responses that end up affecting the endocrine system. Furthermore, sex steroids and corticosteroids may also directly modify the parasite reproduction and molting. Available information indicates that parasites synthesize some steroid hormones, such as ecdysteroids and sex steroids, and the presence and activity of related enzymes have been demonstrated. More recently, the synthesis of corticosteroid-like compounds has been shown in Taenia solium cysticerci and tapeworms, and in Taenia crassiceps WFU cysticerci. In-depth knowledge of the parasite's endocrine properties will contribute to understand their reproduction and reciprocal interactions with the host, and may also help designing tools to combat the infection in some clinical situations.
Highlights
Frontiers in NeuroscienceIt is widely accepted that corticosteroids and sex-related hormones influence the immune response (Roberts et al, 2001; Coutinho and Chapman, 2011; Reyes-Hernandez et al, 2013), thereafter any endocrine perturbation initiated by an infection will change the neuroendocrine equilibrium
Departamento de Fisiología, Biofísica y Neurociencias, CINVESTAV del IPN, Specialty section: This article was submitted to Neuroendocrine Science, a section of the journal
The host gender’s susceptibility to infection, and the related differences in the immune response are good examples of the host-parasite interplay. The capacity of these organisms to synthesize their own steroidogenic hormones still has more questions than answers. It is well-known that many parasites synthesize ecdysteroids, but limited information is available on sex steroid and corticosteroid synthesis
Summary
It is widely accepted that corticosteroids and sex-related hormones influence the immune response (Roberts et al, 2001; Coutinho and Chapman, 2011; Reyes-Hernandez et al, 2013), thereafter any endocrine perturbation initiated by an infection will change the neuroendocrine equilibrium These hormonal changes resulting from a spontaneous or experimental infection, affect the parasitic charge, the course of the infection and the parasite’s survival (Barthelemy et al, 2004). Progesterone, but not testosterone decreased the in vitro molting process of Trichinella spiralis (Hernández-Bello et al, 2011) and T. crassiceps ORF cysticerci cell proliferation was increased by physiological concentrations of testosterone, and 17β-estradiol added to the culture media (Romano et al, 2003), while high concentrations inhibited its reproduction (Escobedo et al, 2004) It is well-known that non-physiological stress situations, such as social isolation, infections, persecution, etc., increase serum corticosteroids levels with the consequent impairment of the immune response.
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