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Ch. 48 - The Immune System in Animals
Freeman - Biological Science 7th Edition
Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook
All textbooksFreeman 7th EditionCh. 48 - The Immune System in AnimalsProblem 14
Chapter 48, Problem 14

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In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?
Parasitic worms modulate their host's immune response by inducing the proliferation of regulatory T cells. What role do these cells play in the adaptive immune response? How could this effect on regulatory T cells be linked to the hygiene hypothesis?

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Regulatory T cells, often referred to as Tregs, are a subset of T cells that play a crucial role in maintaining immune system balance. They help prevent autoimmune diseases by suppressing excessive immune responses that could damage the body's own tissues.
In the context of the adaptive immune response, regulatory T cells modulate the activity of other immune cells, such as helper T cells and cytotoxic T cells, ensuring that the immune response is appropriate and not overly aggressive.
Parasitic worms have been shown to induce the proliferation of regulatory T cells, which can lead to a more controlled immune response. This modulation helps the host tolerate the presence of the parasite without excessive inflammation or tissue damage.
The hygiene hypothesis suggests that a lack of exposure to infectious agents, including parasitic worms, in early childhood can lead to an increased risk of autoimmune and allergic diseases. This is because the immune system may not develop the regulatory mechanisms needed to prevent overreaction to harmless substances.
The link between regulatory T cells and the hygiene hypothesis is that the absence of parasitic worms may result in fewer regulatory T cells, potentially leading to an increased incidence of immune-related disorders. This highlights the importance of a balanced immune system and the potential consequences of reduced exposure to certain pathogens.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Regulatory T Cells

Regulatory T cells (Tregs) are a subset of T cells that play a crucial role in maintaining immune system balance by suppressing excessive immune responses and preventing autoimmune diseases. They help modulate the immune response to prevent damage to the host's own tissues. In the context of parasitic infections, Tregs can be induced to prevent an overactive immune response that could harm the host.
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Helper T Cells and B Cells

Adaptive Immune Response

The adaptive immune response is a highly specific defense mechanism that involves the activation of lymphocytes, such as T cells and B cells, to target and eliminate pathogens. It is characterized by its ability to remember past infections, providing long-lasting protection. Regulatory T cells are integral to this system, ensuring that the response is appropriate and does not target the body's own cells.
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Adaptive Immune Response

Hygiene Hypothesis

The hygiene hypothesis suggests that a lack of exposure to infectious agents, symbiotic microorganisms, and parasites in early childhood can lead to an increased susceptibility to allergic diseases by suppressing the natural development of the immune system. The absence of parasitic worms, which modulate immune responses, may contribute to the rise in autoimmune and allergic conditions in developed countries, as the immune system may become overactive without these regulatory influences.
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Textbook Question

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In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?

What is the hygiene hypothesis? What correlation does it attempt to explain?

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Textbook Question

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In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?

Explain how the adaptive and innate immune responses work together to defend the human body against infection by parasitic worms.

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Textbook Question

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In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?

Pattern-recognition receptors have been identified that recognize worm products. Explain how these receptors are used to activate the adaptive immune response most appropriate for worm infection.

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Textbook Question

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In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?

The roundworm Heligmosomoides polygyrus is a natural intestinal parasite of mice, and it offers an excellent model of the immunology of worm infections in humans. Scientists evaluated the impact of parasitic roundworms on immune disorders using mice prone to developing type 1 diabetes mellitus. Five-week-old mice were infected with H. polygyrus (Hp). Two weeks later, half of the mice were cured of the infection (Rx). When the mice were 40 weeks old, scientists calculated the percentage of mice that developed diabetes in both groups: those exposed to roundworms and those in uninfected control groups (** means P<0.01). What two conclusions are supported by the results shown below?

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Textbook Question

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In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?

There is a strong association between the prevalence of diabetes mellitus in parents and their children. If you were a physician, would you ask parents who have type 1 diabetes to intentionally infect their children with intestinal worms? What additional information would you need to make this decision?

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