What does the evolutionary race theory propose about the relationship between pathogens and their hosts?

It proposes that pathogens and hosts are in a continuous co-evolutionary struggle, with each evolving adaptations in response to the other.

Why does antigenic variation prevent the immune system from recognising a pathogen it has encountered before?

Because the altered surface antigens are no longer recognised by existing memory cells and antibodies, which were specific to the original antigens.

How do some pathogens evade detection by antibodies by exploiting their location?

They hide inside host cells, where antibodies cannot reach them because antibodies cannot cross cell membranes.

How do some pathogens use toxins to interfere with phagocytosis?

They produce toxins that inhibit phagocytosis or prevent the fusion of lysosomes with phagosomes, stopping the digestion of the pathogen.

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Immunity, Infection and Forensics

The evolutionary race and pathogen evasion

2 things to know
Papers 1 and 3

Overview

Recall questions on antigenic variation and other evasion mechanisms, and on what the evolutionary race theory proposes.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is antigenic variation?

Key term

Give an example of a pathogen that directly suppresses the host immune system and explain how it does this.

Questions from this subtopic

Each one with the model answer underneath.

1
What does the evolutionary race theory propose about the relationship between pathogens and their hosts?
Model answer
It proposes that pathogens and hosts are in a continuous co-evolutionary struggle, with each evolving adaptations in response to the other.
2
What is antigenic variation?
Model answer
Antigenic variation is an immune evasion mechanism where pathogens alter their surface antigens over time.
3
Why does antigenic variation prevent the immune system from recognising a pathogen it has encountered before?
Model answer
Because the altered surface antigens are no longer recognised by existing memory cells and antibodies, which were specific to the original antigens.
4
How do some pathogens evade detection by antibodies by exploiting their location?
Model answer
They hide inside host cells, where antibodies cannot reach them because antibodies cannot cross cell membranes.
5
Give an example of a pathogen that directly suppresses the host immune system and explain how it does this.
Model answer
HIV destroys helper T cells, which are essential for coordinating the immune response, thereby suppressing the host's immunity.
6
How do some pathogens use toxins to interfere with phagocytosis?
Model answer
They produce toxins that inhibit phagocytosis or prevent the fusion of lysosomes with phagosomes, stopping the digestion of the pathogen.

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