Immune Tolerance: Videos & Practice Problems

Immune tolerance is crucial for the immune system to differentiate between harmful and harmless antigens, preventing autoimmune diseases. It involves two mechanisms: central immune tolerance, which eliminates self-reacting T and B cells in primary lymphoid organs through negative selection, and peripheral immune tolerance, which occurs in secondary lymphoid organs and includes both positive and negative selection. This strict selection process ensures that only about 5% of T and B cells effectively target harmful antigens, maintaining immune system integrity and function.

Immune Tolerance

Immune tolerance is a crucial function of the immune system, allowing it to differentiate between harmless and harmful antigens. This ability is essential for preventing inappropriate immune responses that could lead to autoimmune diseases, where the body mistakenly attacks its own healthy cells. Immune tolerance can be defined as the immune system's capacity to ignore specific molecules, particularly those that are harmless.

The primary goal of immune tolerance is to ensure that the immune system only targets dangerous antigens, such as pathogens and cancer cells, while ignoring benign substances like normal microflora and healthy self-cells. This selective response is vital for maintaining overall health and preventing unnecessary immune reactions.

In the context of the adaptive immune system, T cells play a significant role in establishing immune tolerance. These cells learn to tolerate harmless antigens, which allows them to focus their efforts on combating harmful invaders. The ability of T cells to distinguish between harmless and harmful antigens is fundamental to the immune system's effectiveness.

In summary, immune tolerance is the mechanism by which the immune system selectively ignores harmless antigens while remaining vigilant against harmful ones. This balance is essential for preventing autoimmune disorders and ensuring a healthy immune response.

Football Analogy for Immune Tolerance

Immune tolerance is a crucial function of the immune system, allowing it to differentiate between harmful and harmless antigens. To illustrate this concept, a football analogy is employed where the immune system is likened to a quarterback (QB) on a football team. In this analogy, harmful antigens are represented as the opposing team, while harmless antigens are depicted as teammates.

Without immune tolerance, the QB (immune system) struggles to identify his teammates from the opponents. This inability to distinguish between harmful and harmless substances can severely impair the immune system's functionality, potentially leading to autoimmune diseases, where the body mistakenly attacks its own cells.

Conversely, when immune tolerance is present, the immune system can effectively recognize and differentiate between harmful and harmless substances. In this scenario, the QB can identify his colorful teammates, enabling him to perform his role effectively. This distinction is vital for the immune system to target and eliminate dangerous antigens while sparing harmless ones.

Ultimately, the football analogy emphasizes the importance of immune tolerance in maintaining a well-functioning immune system, which is essential for protecting the body against threats while avoiding unnecessary attacks on benign substances. As we continue to explore this topic, we will deepen our understanding of immune tolerance and its implications for health.

Central vs. Peripheral Tolerance

Understanding immune tolerance is crucial for comprehending how our body distinguishes between self and non-self cells, preventing autoimmune responses. Immune tolerance can be categorized into two main types: central immune tolerance and peripheral immune tolerance. These mechanisms are essential for the development of T and B cells, which are vital components of the adaptive immune system.

Central immune tolerance occurs in the primary lymphoid organs, specifically the thymus for T cells and the bone marrow for B cells. During this process, a mechanism known as negative selection is employed, where self-reacting T and B cells are eliminated through apoptosis. This ensures that any mature immune cells that bind to self or harmless antigens are removed before they can enter circulation, thus preventing potential damage to healthy tissues.

In contrast, peripheral immune tolerance takes place after T and B cells have matured and left the primary lymphoid organs, moving into secondary lymphoid organs such as lymph nodes. This phase involves both positive and negative selection. Positive selection promotes the survival of T cells that can adequately bind to Major Histocompatibility Complex (MHC) molecules, which is crucial for their activation. Conversely, negative selection in the peripheral context eliminates T cells that react to harmless self antigens, leading to anergy or apoptosis of these self-reacting cells.

It is noteworthy that approximately 95% of T and B cells generated initially undergo apoptosis due to these stringent tolerance mechanisms, allowing only about 5% to survive and function effectively. This small percentage is critical, as these cells are well-equipped to respond appropriately to harmful antigens while avoiding attacks on the body’s own healthy cells.

In summary, central and peripheral immune tolerance are vital processes that ensure the adaptive immune system functions correctly, minimizing the risk of autoimmune diseases. By rigorously selecting T and B cells based on their reactivity to antigens, the body maintains a delicate balance between immune activation and self-tolerance, which is essential for overall health.

The most important function of peripheral tolerance is to:

• A. Eliminate mature B & T lymphocytes that bypassed central tolerance from reacting to self-cells.
• B. Eliminate inactive B & T lymphocytes from peripheral blood.
• C. Eliminate self-reacting B & T lymphocytes before they enter central tolerance.
• D. Eliminate mature B & T lymphocytes from the bone marrow.

Answer: (A)

Where do T cells undergo central tolerance selection?

• A. Bone marrow.
• B. Pancreas.
• C. Thymus.
• D. Liver.
• E. Brain.

Answer: (C)

What is immunological tolerance?

• A. The ability of the immune system to remove lymphocytes that recognize and attack foreign antigens.
• B. The ability of the immune system to differentiate between self and non-self antigens.
• C. The ability of the immune system to create antibodies that most effectively bind foreign antigens.
• D. The ability of the immune system to tolerate a certain amount of pathogens before triggering an immune response.

Answer: (B)

Which of the following is NOT a consequence of the immune system lacking an immune tolerance?

• A. The immune system cells will only recognize and attack foreign antigens.
• B. The immune system cells will recognize and attack foreign and self-antigens.
• C. The immune system will attack self-cells causing autoimmune diseases.
• D. The immune system will not remove T and B lymphocytes that bind to self-antigens.

Answer: (A)

Here’s what students ask on this topic:

What is immune tolerance and why is it important?

Immune tolerance is the ability of the immune system to distinguish between harmful and harmless antigens, allowing it to ignore harmless substances while targeting harmful ones. This is crucial to prevent the immune system from attacking the body's own healthy cells, which can lead to autoimmune diseases. Without immune tolerance, the immune system would struggle to differentiate between self and non-self, resulting in inappropriate immune responses. By building tolerance to harmless antigens, the immune system maintains its integrity and function, ensuring that only harmful pathogens are targeted and destroyed.

What are the differences between central and peripheral immune tolerance?

Central immune tolerance occurs in primary lymphoid organs (bone marrow for B cells and thymus for T cells) and involves negative selection, where self-reacting T and B cells are eliminated through apoptosis. Peripheral immune tolerance takes place in secondary lymphoid organs (e.g., lymph nodes) and includes both positive and negative selection. Positive selection promotes cells that bind appropriately to MHC molecules, while negative selection eliminates cells that react to harmless antigens. Together, these mechanisms ensure that only a small percentage of T and B cells, which can effectively target harmful antigens, survive and function properly.

How does the immune system distinguish between harmful and harmless antigens?

The immune system distinguishes between harmful and harmless antigens through a process called immune tolerance. This involves two main mechanisms: central tolerance and peripheral tolerance. Central tolerance occurs in the primary lymphoid organs, where self-reacting T and B cells are eliminated. Peripheral tolerance occurs in secondary lymphoid organs and involves both positive and negative selection. Positive selection promotes cells that bind appropriately to MHC molecules, while negative selection eliminates cells that react to harmless antigens. These processes ensure that the immune system can effectively target harmful pathogens while ignoring harmless substances.

What role do T cells and B cells play in immune tolerance?

T cells and B cells are crucial in immune tolerance. During their development in primary lymphoid organs (thymus for T cells and bone marrow for B cells), they undergo central tolerance, where self-reacting cells are eliminated through negative selection. In secondary lymphoid organs, they undergo peripheral tolerance, which includes both positive and negative selection. Positive selection promotes cells that bind appropriately to MHC molecules, while negative selection eliminates cells that react to harmless antigens. This strict selection process ensures that only T and B cells capable of targeting harmful antigens survive, maintaining immune system integrity and function.

What happens if immune tolerance fails?

If immune tolerance fails, the immune system may not properly distinguish between harmful and harmless antigens, leading to inappropriate immune responses. This can result in the immune system attacking the body's own healthy cells, causing autoimmune diseases. Without effective immune tolerance, self-reacting T and B cells may survive and proliferate, leading to chronic inflammation and tissue damage. Therefore, maintaining immune tolerance is essential for preventing autoimmune diseases and ensuring that the immune system targets only harmful pathogens while ignoring harmless substances.