Third Line of Defense

Exam Revision

What is the third line of defence?

The third line of defence is the specific immune response that targets particular pathogens using specialised white blood cells.

Why is the third line of defence called specific?

Because it recognises and responds to specific pathogens rather than attacking all pathogens in the same way.

How does the third line of defence work?

Specialised white blood cells recognise a specific pathogen, produce a targeted response, and help destroy that pathogen.

What is the main difference between the second and third lines of defence?

The second line is non-specific and responds the same way to all pathogens, while the third line is specific and targets particular pathogens.

What is the role of the third line of defence?

To identify specific pathogens and mount a targeted immune response that removes them from the body.

What are B-cells?

B-cells are a type of white blood cell involved in the third line of defence that produce antibodies against specific pathogens.

What is the role of B-cells in the immune system?

B-cells produce antibodies that specifically target and help destroy pathogens.

How do B-cells help fight infection?

When they recognise a specific pathogen, B-cells produce antibodies that bind to that pathogen and help the immune system eliminate it.

Why are B-cells part of the specific immune response?

Because they produce antibodies that target specific pathogens rather than all pathogens.

What are antibodies?

Antibodies are proteins produced by B-cells that recognise and bind to specific pathogens.

What do antibodies do?

Antibodies bind to specific pathogens and mark them for destruction by the immune system.

Why are antibodies considered specific?

Each antibody is designed to bind to a particular pathogen (or antigen), allowing the immune system to target the correct invader.

How are B-cells and antibodies related?

B-cells produce antibodies that attach to specific pathogens and help the immune system destroy them.

What is the difference between the second and third lines of defence?

Second line of defence: Non-specific; responds the same way to all pathogens (e.g. phagocytes and inflammation).

Third line of defence: Specific; targets particular pathogens using B-cells and antibodies.

Which line of defence is specific and which is non-specific?

The second line is non-specific, while the third line is specific.

What are the two main roles of the third line of defence?

Identify and destroy specific pathogens.

Build long-lasting immunity in case the same pathogen infects the body again.

Why does the third line of defence provide long-lasting protection?

It creates immunity, allowing the immune system to respond more effectively if the same pathogen enters the body again.

How does the immune system recognise pathogens?

The immune system recognises molecules that do not belong in the body ("non-self"), such as antigens on the surface of pathogens.

What is an antigen?

An antigen is a foreign molecule or surface marker on a pathogen that can be recognised by the immune system.

Why can the immune system tell different pathogens apart?

Different pathogens have different antigens on their surfaces.

What does "non-self" mean in immunity?

"Non-self" refers to substances or molecules that do not belong to the body and may trigger an immune response.

What do antibodies recognise and bind to?

Antibodies recognise and bind to specific antigens on pathogens.

How are B-cells able to recognise specific pathogens?

Each B-cell has a unique antibody on its surface that matches and recognises a specific antigen on a pathogen.

Why do antibodies only bind to specific pathogens?

Because each antibody has a unique shape that only matches a specific antigen (lock-and-key mechanism).

What is the lock-and-key model in immunity?

It describes how antibodies have specific shapes that only fit and bind to matching antigens on pathogens.

How do B-cells relate to antibodies?

Each B-cell produces a unique antibody that targets a specific antigen.

What happens when a B-cell recognises a specific pathogen?

It binds to the pathogen and then divides to produce many identical copies (clones).

What is clonal expansion?

Clonal expansion is when a B-cell rapidly divides to produce many identical cells that recognise the same pathogen.

What do cloned B-cells do?

They release large numbers of antibodies that specifically target the pathogen.

Why is clonal expansion important?

It quickly produces many antibodies to fight the infection effectively.

How do antibodies help fight pathogens?

Antibodies bind to pathogens and neutralise them, preventing them from harming cells.

What does it mean to neutralise a pathogen?

It means blocking the pathogen so it can no longer infect or damage body cells.

How do antibodies help phagocytes?

They bind to pathogens and mark them, making it easier for phagocytes to recognise and destroy them.

What is the overall effect of antibodies?

They neutralise pathogens and help the immune system destroy them more efficiently.

How is the third line of defence different from the first and second lines?

The first and second lines are non-specific and respond the same way to all pathogens, while the third line is specific and targets particular pathogens.

Why is the third line of defence slower at first?

Because B-cells must recognise the pathogen, divide, and produce enough antibodies before the pathogen is fully destroyed.

Why do you feel ill before the third line of defence fully responds?

Because it takes time for B-cells to make enough antibodies to fight the specific pathogen effectively.

Compare speed and specificity of the immune system lines of defence.

First and second lines are fast and non-specific. The third line is slow but specific.

What is immunity?

Immunity is when the body can resist a specific pathogen after being exposed to it, so it does not become ill again.

What happens after an infection is cleared?

Some antibodies remain in the blood and some B-cells remain as memory cells.

What are memory cells?

Memory cells are long-lasting B-cells that "remember" a specific pathogen and respond faster if it enters the body again.

Why do memory cells prevent you from getting sick again?

They allow the immune system to produce antibodies much faster, destroying the pathogen before symptoms develop.

How is a second infection different from the first infection?

The second response is much faster because memory cells quickly produce antibodies, preventing illness.