The Immune System and B Cells

Questions and Answers

What is the main purpose of the immune system?

To fight foreign substances such as bacteria and viruses (correct)

To attack the body's own cells

To distinguish self from non-self only

To produce antibodies for no reason

What is a critical aspect of B cell receptors and antibodies?

They only bind to self-cells

They are produced in a specific order

They are generated at random (correct)

They are identical in all B cells

What do antibodies bind to?

The body's own cells

Other B cells

Foreign proteins or cells (correct)

The nucleus of the B cell

What is the significance of the B cell receptor?

It binds to foreign substances, activating an immune response Signup and view all the answers

Why is it challenging for the immune system to distinguish self from non-self?

Because B cell receptors are generated randomly Signup and view all the answers

What is unique about each B cell?

Its DNA and B cell receptor Signup and view all the answers

What is the role of the B cell nucleus?

To contain the B cell's DNA Signup and view all the answers

How do B cells acquire their unique B cell receptors?

Through the shuffling of DNA Signup and view all the answers

What is the main reason why the body is in danger of creating B cell receptors and antibodies that can react to its own body?

Because the creation of B cell receptors and antibodies is a totally random process Signup and view all the answers

What would happen if a B cell receptor reacts to insulin?

The B cell would start creating antibodies that bind to insulin, preventing it from doing its function Signup and view all the answers

Why is it important to have a mechanism to get rid of B cells that react to self?

Because it prevents the body from attacking itself Signup and view all the answers

Where do B cells get their unique antibody, or B cell receptor?

In the bone marrow Signup and view all the answers

What is the purpose of keeping various proteins around in the bone marrow during B cell development?

To identify and eliminate B cells that react to self Signup and view all the answers

What happens to B cells that bind to proteins in the bone marrow during development?

They are killed Signup and view all the answers

Why is it equally applicable to talk about T cells in this context?

Because T cells also have a T cell receptor that is generated at random Signup and view all the answers

What would happen if the body did not have a way to eliminate B cells that react to self?

The body would start attacking itself Signup and view all the answers

How are B cell receptors and antibodies created?

Through a totally random process Signup and view all the answers

What is the purpose of the process of eliminating B cells that react to self in the bone marrow?

To prevent the body from attacking itself Signup and view all the answers

What happens to B cells that recognize self-molecules in the bone marrow?

They are killed to prevent self-reaction Signup and view all the answers

Why does the weeding out process of B cells that react to self-proteins not happen in the lymph node?

The lymph node has a different environment Signup and view all the answers

What is the purpose of B cells presenting proteins on MHC II molecules?

To activate T cells Signup and view all the answers

What happens to T cells that react to self-proteins in the thymus?

They are killed to prevent self-reaction Signup and view all the answers

Why can't B cells that escape the weeding out process in the bone marrow activate without T cells?

Because they need T cells to recognize the antigen Signup and view all the answers

What is the second mechanism of defense against self-reaction?

Activation of B cells by T cells Signup and view all the answers

Where does the 'cellular kiss' between B cells and T cells usually occur?

In the lymph node Signup and view all the answers

What happens to B cells that do not react to self-proteins in the bone marrow?

They mature and proceed to the lymph node Signup and view all the answers

Why is it necessary to have both mechanisms of defense against self-reaction?

To prevent mistakes in the weeding out process Signup and view all the answers

What is the purpose of the weeding out process of B cells that react to self-proteins?

To prevent self-reaction Signup and view all the answers

What is a possible consequence if bacteria enter the bone marrow?

The B cells that react to the bacterium will be killed, but the infection will be fought by other B cells in the lymph nodes. Signup and view all the answers

Why is autoimmune disease not a significant problem in this scenario?

The body has mechanisms to prevent autoimmune disease. Signup and view all the answers

What happens to the receptor on the muscle fiber in myasthenia gravis?

It is destroyed by the antibodies. Signup and view all the answers

What is the result of myasthenia gravis?

Muscle fibers become weaker, leading to paralysis. Signup and view all the answers

What is the significance of B cells already present in the lymph nodes?

They can lead the battle against the infection while the bone marrow is prevented from producing more B cells. Signup and view all the answers

What is the primary function of the receptor on the muscle fiber?

To receive signals from neurons and activate the muscle fiber. Signup and view all the answers

What happens if the bacterium remains in the bone marrow for an extended period?

The B cells in the bone marrow that react to the bacterium will be killed, and production of new B cells will be halted. Signup and view all the answers

What is the consequence of autoimmune disease?

The immune system starts attacking the body's own cells and tissues. Signup and view all the answers

Why can the body still fight the infection even if the B cells in the bone marrow are killed?

The B cells in the lymph nodes can still proliferate to fight the infection. Signup and view all the answers

What is the significance of the example of myasthenia gravis?

It is an example of autoimmune disease, where the immune system attacks the body's own cells and tissues. Signup and view all the answers

What is the main challenge of the immune system?

To distinguish self from non-self Signup and view all the answers

How are B cell receptors and antibodies generated?

Through a random process Signup and view all the answers

What would happen if the immune system failed to distinguish self from non-self?

The body would attack its own cells and tissues Signup and view all the answers

What is unique about each B cell?

Its B cell receptor Signup and view all the answers

Why is it important for the immune system to distinguish self from non-self?

To prevent autoimmune diseases Signup and view all the answers

What happens to the B cell receptor once it becomes active?

It is released as an antibody Signup and view all the answers

Why is the process of distinguishing self from non-self not obvious?

Because B cells have unique receptors Signup and view all the answers

What is the significance of the B cell receptor?

It helps the immune system fight bacteria and viruses Signup and view all the answers

What happens to B cells that react to self in the bone marrow?

They are killed as a result of binding to self-proteins. Signup and view all the answers

Why is it challenging to create a B cell receptor that only reacts to non-self?

Because B cell receptors are created at random. Signup and view all the answers

What is the purpose of keeping various proteins around in the bone marrow during B cell development?

To eliminate B cells that react to self-proteins. Signup and view all the answers

What would happen if a B cell receptor reacts to insulin?

The B cell would be activated to produce antibodies that react to insulin. Signup and view all the answers

Why is it important to eliminate B cells that react to self?

To prevent autoimmune diseases. Signup and view all the answers

What is unique about each B cell?

Its unique B cell receptor. Signup and view all the answers

Why is it equally applicable to talk about T cells in this context?

Because T cells also have a unique receptor generated at random. Signup and view all the answers

What happens to B cells that bind to self-proteins in the bone marrow?

They are eliminated through apoptosis. Signup and view all the answers

What is the significance of the process of eliminating B cells that react to self-proteins?

It prevents autoimmune diseases from occurring. Signup and view all the answers

What would happen if the body did not have a way to eliminate B cells that react to self-proteins?

Autoimmune diseases would occur more frequently. Signup and view all the answers

What happens to B cells that recognize self-molecules in the bone marrow?

They are killed Signup and view all the answers

Why doesn't a B cell die when it interacts with a bacterium it's meant to fight?

Because it's in a different environment with different rules Signup and view all the answers

What is the purpose of a B cell presenting a protein on an MHC II molecule?

To activate a T cell that recognizes the protein Signup and view all the answers

What happens to T cells that react to self-proteins in the thymus?

They are killed Signup and view all the answers

What is the second mechanism of defense against self-reaction?

The need for a T cell to activate a B cell that reacts to self Signup and view all the answers

Why is it necessary to have both mechanisms of defense against self-reaction?

Because the weeding out process is not foolproof Signup and view all the answers

Where does the 'cellular kiss' between B cells and T cells usually occur?

In a lymph node Signup and view all the answers

What happens to a B cell that escapes the weeding out process in the bone marrow?

It needs a T cell to activate it Signup and view all the answers

Why is it important to have a mechanism to eliminate B cells that react to self?

To prevent autoimmune diseases Signup and view all the answers

What is the purpose of the weeding out process of B cells that react to self-proteins?

To prevent autoimmune reactions Signup and view all the answers

What happens to B cells that bind to a bacterium in the bone marrow?

They are killed because they are in the binding stage Signup and view all the answers

Why is autoimmune disease not a significant problem in the scenario where bacteria enter the bone marrow?

Because the infection is cleared quickly and B cells can be produced again Signup and view all the answers

What is the result of the autoimmune disease myasthenia gravis?

Muscle weakness and paralysis over time Signup and view all the answers

Why are B cells already present in the lymph nodes significant?

They can proliferate and lead the battle against the infection Signup and view all the answers

What happens to the receptor on the muscle fiber in myasthenia gravis?

It is blocked or destroyed by antibodies Signup and view all the answers

Why can the body still fight the infection even if the B cells in the bone marrow are killed?

B cells in the lymph nodes can still react to the bacterium Signup and view all the answers

What happens if the bacterium remains in the bone marrow for an extended period?

The bone marrow stops producing B cells Signup and view all the answers

What is the primary function of the receptor on the muscle fiber?

To receive signals from the neuron and activate the muscle fiber Signup and view all the answers

What is the consequence of autoimmune disease?

The immune system attacks the body's own tissues and organs Signup and view all the answers

Why is it possible for autoimmune disease to occur?

Because the immune system is not able to distinguish self from non-self Signup and view all the answers

Study Notes

The Immune System and Self

The immune system's purpose is to fight foreign substances (bacteria, viruses, etc.) that enter the body
The immune system must distinguish between "self" (one's own body) and "non-self" (foreign substances) to avoid attacking itself

B Cells and Antibodies

B cells have unique receptors that bind to foreign substances (antigens)
B cell receptors are generated randomly and are different for each B cell
B cells can create antibodies that bind to specific antigens
Antibodies can react to both foreign substances and self-antigens (proteins in one's own body)

Random Creation of B Cell Receptors

The random creation of B cell receptors means that some may react to self-antigens
This poses a risk of the immune system attacking itself
There is no way to prevent the creation of B cells that react to self-antigens

Eliminating Self-Reactive B Cells

In the bone marrow, B cells are vetted to remove those that react to self-antigens
Proteins from the body are present in the bone marrow to test B cells
B cells that bind to self-antigens are killed
This process is not foolproof, and some self-reactive B cells may escape

T Cells and Self-Reactive Immunity

T cells also have unique receptors that are generated randomly
T cells can react to both foreign substances and self-antigens
The process of eliminating self-reactive T cells occurs in the thymus

Second Mechanism of Defense

Even if a self-reactive B cell escapes, it usually requires a T cell to activate it
The activation process involves the B cell presenting a piece of the self-antigen on an MHC II molecule
The T cell must recognize the self-antigen and interact with the B cell to activate it
This second mechanism of defense provides an additional layer of protection against self-reactive immunity

Autoimmune Disease

Despite these mechanisms, the immune system can still attack itself, leading to autoimmune disease
Autoimmune disease occurs when the immune system mistakenly attacks the body's own tissues and organs
One example of an autoimmune disease is myasthenia gravis, which is characterized by muscle weakness caused by antibodies against muscle receptors

The Immune System and Self vs Non-Self

The immune system's purpose is to fight foreign substances like bacteria and viruses, but it needs to distinguish between self and non-self to avoid attacking the body itself.
The question of how the immune system knows not to attack itself is not obvious, and the answer lies in how B cells and T cells are generated and controlled.

B Cells and Antibodies

B cells have unique B cell receptors that bind to foreign substances, which later become antibodies that help remove them from the body.
Each B cell has a different receptor, generated at random through DNA shuffling, which means some might react to the body's own proteins and cells.
This random generation process puts the body at risk of creating B cells and antibodies that react to self, which could lead to autoimmune diseases.

Preventing Self-Attack

The body has mechanisms to prevent B cells that react to self from being activated:
- In the bone marrow, where B cells mature, the body keeps a selection of its own proteins to test the B cells' receptors. If a B cell binds to one of these proteins, it is killed.
- This process weeds out B cells that react to self, ensuring that only those that react to non-self proteins and cells are activated.
The same process occurs for T cells, which mature in the thymus and are also tested for self-reactivity.

Second Mechanism of Defense

Even if a B cell that reacts to self escapes the bone marrow, it usually needs a T cell that also reacts to self to activate it.
This second mechanism of defense ensures that most autoimmune reactions are prevented, as both a B cell and a T cell need to escape their respective weeding-out processes to trigger an immune response.

What Can Go Wrong

If bacteria infect the bone marrow, B cells that react to the bacteria might be killed, making it harder for the body to fight the infection.
Autoimmune diseases can still occur when the body's mechanisms fail, leading to the immune system attacking the body's own cells and tissues.
An example of autoimmune disease is myasthenia gravis, where antibodies attack the receptors on muscle fibers, preventing muscle activation and leading to muscle weakness.

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Description

Learn about the immune system's role in distinguishing between self and non-self, and how B cells and antibodies fight foreign substances.