The specific immune system

Health, disease and the development of medicines · Human defences and immunity · note 2 of 3

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The specific immune systemSpec 5.13

In short

The specific immune system responds to one particular pathogen. Antigens on the pathogen trigger lymphocytes to produce antibodies, which bind to the antigens and help destroy it. Memory lymphocytes are also made. If the same pathogen returns, they give a faster secondary response with more antibodies, so the person does not become ill.

If a pathogen gets past the first defences, the specific immune system responds. It is called specific because the response is aimed at one particular pathogen.

Antigen: A molecule, usually on the surface of a pathogen, that the immune system recognises as foreign and that triggers an immune response.
Antibody: A protein made by white blood cells (lymphocytes) that binds to a specific antigen.
Memory lymphocyte: A white blood cell that stays in the body after an infection and can respond quickly if the same antigen returns.

The primary response

The body is exposed to a pathogen.
The antigens on the pathogen trigger an immune response.
Lymphocytes with antibodies that fit the antigen divide, and the response causes the production of antibodies.
The antibodies bind to the antigens on the pathogen and help to destroy it.
The antigens also trigger production of memory lymphocytes.

The secondary response

If the same pathogen enters the body again, the memory lymphocytes recognise its antigens. They respond faster and make more antibodies than the first time, so the pathogen is destroyed before it can make the person ill. The person is now immune to that pathogen.

Exam tip:

For the secondary response, write three things: it is quicker, more antibodies are made, and memory lymphocytes are responsible.

Graph of antibody concentration in the blood against time, showing a small, slow primary response after the first exposure to an antigen and a much faster, higher secondary response after the second exposure to the same antigen. — Memory lymphocytes make the secondary response faster and bigger than the primary response.

Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026

Frequently asked questions

How do vaccines work?

Vaccines work by putting an inactive form of a pathogen, such as a dead or weakened one, into the body. Its antigens trigger an immune response, so antibodies and memory lymphocytes are made. If the live pathogen enters later, memory lymphocytes carry out a fast secondary response with many antibodies, so the person does not become ill.

How do white blood cells fight infection?

White blood cells called lymphocytes fight infection by producing antibodies. Antigens on a pathogen trigger the lymphocytes with antibodies that fit to divide, and antibodies are produced. The antibodies bind to the antigens and help destroy the pathogen. Memory lymphocytes are also made, so the response is faster if the pathogen returns.

What is the difference between the primary and secondary immune response?

The primary response happens the first time a pathogen enters the body, and the person usually becomes ill while antibodies are made. In the secondary response, memory lymphocytes recognise the same antigens and respond faster, making more antibodies, so the pathogen is destroyed before it can make the person ill.

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