(4) Introduction to the body's immune System

(a) Introduction: What is the primary function of the immune system?

What is the immune system? Why is it needed?

White blood cells fight infections in three ways.

They can surround, destroy and digest pathogens.

They produce antibodies to combat pathogens.

They produce antitoxins to counteract toxins produced by invading bacteria.

Pathogens like bacteria make us feel unwell because their cellular chemistry releases toxins into our body.

The body has an immune system that that recognises and destroys invasive pathogens.

Phagocyte white blood cells can destroy pathogens by directly killing them.

Lymphocyte white blood cells produce antibodies to destroy pathogens and antitoxins to neutralise the toxic waste from pathogens.

So, the immune system 'kicks in' if pathogens do get inside your body.

The white blood cells are present throughout your body in your blood system and therefore are always at hand to defend you from invading pathogens and the do so in three main ways - see sections (i) to (v) below.

Only about 1% of blood cells are white, the majority are oxygen carrying red blood cells.

If your white blood cell count is low you are more susceptible to disease and infection, because this equates to a weakening of your immune response system

 

For example, HIV/AIDS weakens white cell action and hence the body's immune response to infection.

HIV/AIDS disease destroys white blood cells weaker responding immune system that allows pathogens to have a more devastating effect on the body.

They cannot make enough effective antibodies to counteract a pathogen infection.

Sufferers from HIV/AIDS have insufficient lymphocytes to recognise common infections and produce the necessary antibodies - sometimes with fatal consequences from a disease that in a healthy body would not have proved fatal.

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(b) The immune system of the body produces specific antibodies to kill a particular pathogen.

This leads to immunity from that pathogen.

In some cases, dead or inactivated pathogens stimulate antibody production - vaccination - immunisation.

If a large proportion of the population is immune to a pathogen, the spread of the pathogen is very much reduced - this is known as herd immunity, which can arise either from mass vaccination or naturally if a high percentage of the population develop natural immunity to a pathogen - in either case, lots of people have the antibodies to combat the pathogen and therefore far less people can be carriers of the pathogen.

 

More details on the functions of the white blood cells of the immune system

What is the function of white blood cells?

If pathogens like harmful bacteria actually get into your body your immune system responds to destroy them to defend you from their harmful effects.

The most important feature of your immune system is the function of the different types of white blood cells.

These white blood cells are travelling around the whole of your body in your bloodstream and so are always available to tackle an infection.

More of the types of white blood cells can be made to tackle any major infection, but infections may take time to be cleared up completely.

When white blood cells meet an invading pathogen (bacteria, virus etc.) they can respond in three different ways.

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This page is only an introduction,

so, for all the details of the actions of the immune system

Read Parts 5 to 7 from the index

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Key points Source of information is based on textbooks & syllabus-specifications for students taking the AQA GCSE, Edexcel GCSE and OCR GCSE level biology examinations (~US grades 9-10).

Key points about the immune system (see other pages for detailed examples)

This is a foundational topic that connects directly to how your body defends against disease and links to vaccination, antibiotics, and more advanced immune responses.

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Introduction to the Immune System

The immune system is the body’s complex defence mechanism against pathogens (disease-causing microorganisms like bacteria, viruses, fungi, and parasites).

It consists of cells, tissues, and organs working together to identify, attack, and destroy harmful invaders.

There are two main types of immune responses:

1. Non-specific immunity – The first line of defence that doesn’t distinguish between different pathogens.

2. Specific immunity – Targets particular pathogens using white blood cells (lymphocytes) and antibodies.

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Key Components of the Immune System

1. White Blood Cells (WBCs)

These are the main defenders in the bloodstream and lymphatic system.

Types of white blood cells:

• Phagocytes (e.g. neutrophils):

  • Perform phagocytosis – engulf and digest pathogens.

  • Non-specific: they attack any harmful invader.

• Lymphocytes:

  • Produce antibodies that lock onto specific antigens on pathogens.

  • Produce antitoxins to neutralise toxins.

  • Remember pathogens for faster response in future infections (immunological memory).

2. Antigens and Antibodies

• Antigens – proteins on the surface of pathogens that the immune system recognises as foreign.

• Antibodies – proteins made by lymphocytes that are specific to a particular antigen, locking onto it and tagging it for destruction.

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Why This Topic Matters for Biology

It connects across topics:

• Links to vaccination, antibiotics, drug development, and hygiene.

• Essential for understanding how diseases are prevented and controlled.

Exam Relevance:

• Questions often ask to compare phagocytes and lymphocytes, or to describe how antibodies work.

• Diagrams of immune responses (like antibody-antigen binding) are common.

Real-world application:

• Helps explain how vaccines trigger immunity without causing illness.

• Clarifies how the immune system can fail (e.g. HIV attacks lymphocytes) or overreact (e.g. allergies).

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Quick Summary Table

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Learning objectives for this section on the immune system

Know how body's immune system functions, and what it can do i.e. its primary function is to defend against pathogens.

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