Introduction
Parasites are living organisms that reside on or inside a host organism, acquiring nourishment and other advantages from the host. The relationship between parasites and their hosts is intricate and multidimensional, and each organism has a unique impact on the other. The impact of steroid hormones on the growth and survival of parasites is an essential aspect of this interaction.
Steroid hormones, synthesized by the adrenal gland and gonads, fulfill crucial roles in regulating diverse physiological processes in humans and other animals. In parasitic infections, steroid hormones can influence the host's immune response and the parasite's ability to survive and reproduce within the host.
What Is the Mechanism of Action of Steroid Hormones in Parasitic Infections?
Cortisol, testosterone, and estrogen are steroid hormones that can modify how the host immune system reacts to parasitic diseases.
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Cortisol is an anti-inflammatory hormone that suppresses immune cell function, including the production of cytokines and the activation of T cells.
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Parasites such as Plasmodium falciparum can stimulate the host's adrenal gland to produce cortisol, suppressing the host's immune response and promoting the parasite's survival within the host.
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Testosterone has been shown to enhance the immune response to Leishmania primary infection.
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Estrogen has been shown to suppress the immune response to Schistosoma mansoni infection.
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Parasites may manipulate the host's cortisol response by activating the hypothalamic-pituitary-adrenal (HPA) axis, leading to the production of cortisol by the adrenal gland.
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Parasites can generate molecules that imitate or trigger the host's stress response, activating the HPA axis and releasing cortisol.
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Parasites may also directly interact with the host's immune system to suppress the immune response, for example, by secreting proteins that inhibit the production of cytokines by immune cells.
How Do Steroid Hormones Affect the Development of Parasitic Infections?
The interaction between parasites and the host immune system is complex, and parasites have evolved mechanisms to evade or manipulate host immune responses to ensure their survival and propagation.
One such mechanism is manipulating host steroid hormone responses, which can influence immune cell function and modulate the host immune response to parasitic infections.
1. Cortisol:
The glucocorticoid hormone cortisol is a crucial regulator of the host immune reaction. In reaction to stress, the adrenal gland releases cortisol, which regulates numerous physiological processes like metabolism, inflammation, and immune cell function.
Cortisol has anti-inflammatory effects and can suppress immune cell function, including the production of cytokines and the activation of T cells. It has been demonstrated that parasites like Plasmodium falciparum take advantage of the host's cortisol reaction.
When the host is infected with malaria, the parasite can cause the adrenal gland to create cortisol, suppressing the host's immune response and aiding the parasite's survival inside the host. Cortisol levels are frequently high in malaria patients, linked to worse outcomes and worsening illness.
Glucocorticoids like cortisol can inhibit the development and reproduction of the tapeworm Hymenolepis diminuta, androgens like testosterone can stimulate these processes.
2. Testosterone:
Testosterone has been shown to enhance the immune response to Leishmania primary infection by increasing the production of cytokines, such as IFN-γ and TNF-α, which are immune cells released in response to Leishmania infection. These cytokines activate macrophages, which play a critical role in the clearance of Leishmania parasites.
3. Estrogen:
Estrogen has also been shown to influence parasite development and survival in various ways. For example, estrogen can increase the susceptibility of female mice to infection with the protozoan parasite Toxoplasma gondii while enhancing the survival and reproduction of the liver fluke Opisthorchis viverrini in female hosts.
What Is the Outcome Effect of Steroid Hormones on Parasitic Infection?
These effects on the immune response can have important implications for the outcome of the infection, with steroid hormones either promoting or hindering parasite survival and reproduction.
Steroid hormones can directly affect parasite development and survival and modify the host's immune reaction. For instance, glucocorticoids like cortisol can inhibit the growth and reproduction of the tapeworm Hymenolepis diminuta, androgens like testosterone can stimulate these processes.
Here are some general outcomes that have been observed in studies:
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Immune Suppression: Cortisol is a potent immunosuppressant that can inhibit the function of immune cells and suppress inflammation.
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Immune Enhancement: Testosterone has been shown to enhance the immune response to some parasitic infections, such as Leishmania major.
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Host Susceptibility: Hormones may influence host susceptibility to parasitic infections by altering the gene expression involved in immune function or affecting the production of antimicrobial peptides.
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Gender-Specific Effects: Some parasitic infections, such as Schistosoma mansoni, have been shown to have gender-specific effects on the host immune response.
What Is the Steroid Synthesis Seen in Parasites?
1. Corticosteroid:
It was found that Taenia solium, Taenia crassiceps cysticerci, and tapeworms can synthesize corticosteroids, a type of steroid hormone.
When 3H-progesterone was added to Taenia crassiceps cysticerci, it was transformed into deoxycorticosterone and corticosterone.
Similarly, corticosteroid-like synthesis was found in Taenia solium tapeworms. These hormones could affect the development and differentiation of the parasites, as well as their ability to survive in the host's tissues.
2. Sex Steroids:
It has been discovered that a number of parasites, including Schistosoma mansoni, Trypanosoma cruzi, Taenia solium, and Taenia crassiceps WFU, can produce androgens and estrogens from steroid precursors.
In the case of Taenia solium and Taenia crassiceps WFU, their cysticerci and tapeworms were found to have the capacity to transform steroid precursors into androgens and estrogens.
The presence and activity of enzymes from the Δ5 steroid pathway (a biochemical process that converts cholesterol to androgen and estrogen hormones) were also detected in Taenia crassiceps WFU tapeworms, which suggests their steroidogenic capacity.
Conclusion
In conclusion, steroid hormones are essential in the host's response to parasitic infections. They are involved in modulating the immune response and regulating the host's metabolic response to infection. The synthesis of steroid hormones by parasites is a relatively understudied area, but emerging evidence suggests that it may play an essential role in parasite physiology and development. The ability of parasites to produce steroids may allow them to manipulate the host's immune response or promote their reproductive success within the host.
