How does the immune system target a specific pathogen and remember it?
The specific immune response by lymphocytes, including antigens, the action of B lymphocytes (antibody production) and T lymphocytes (destroying infected cells), clonal selection, immunological memory, allergy and autoimmune disease.
An SQA Higher Human Biology answer on specific cellular defences, covering antigens, the roles of B and T lymphocytes, antibody production, the destruction of infected cells, clonal selection, immunological memory and the secondary response, allergy and autoimmune disease.
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What this dot point is asking
The SQA wants you to explain how antigens trigger the specific immune response, describe the roles of B lymphocytes (antibody production) and T lymphocytes (destroying infected cells), explain clonal selection and immunological memory, and describe allergy and autoimmune disease.
Antigens and lymphocytes
The specific response depends on recognising the antigens of a particular pathogen. Each lymphocyte is specific to one antigen, so the body holds a huge variety of lymphocytes ready to respond to many different pathogens.
B and T lymphocytes
There are two main kinds of lymphocyte, with different jobs:
So B lymphocytes deal with pathogens in the blood and tissue fluid (through antibodies), while T lymphocytes deal with cells that have already been infected.
Clonal selection and immunological memory
When the matching lymphocyte is selected, it divides rapidly to produce many copies. Some of these become memory cells, which survive long after the infection has been cleared.
When the system goes wrong
The specific immune system can malfunction in two ways:
- In an allergy, the immune system overreacts to a harmless antigen (an allergen) such as pollen, triggering symptoms like sneezing through histamine release.
- In an autoimmune disease, the immune system fails to recognise the body's own cells as self and attacks them, damaging healthy tissue (for example, type 1 diabetes, where the insulin-producing cells are destroyed).
Examples in context
Example 1. Recovering from chickenpox once. After a first infection with the chickenpox virus, memory cells remain. If the virus is met again, the fast, strong secondary response destroys it before symptoms develop, which is why most people catch chickenpox only once.
Example 2. Type 1 diabetes as autoimmunity. In type 1 diabetes the immune system attacks and destroys the insulin-producing cells of the pancreas, mistaking them for non-self. This autoimmune attack is why no insulin can be made, linking immunity to blood glucose control.
Try this
Q1. State which type of lymphocyte produces antibodies. [1 mark]
- Cue. B lymphocytes.
Q2. Explain why the secondary immune response is faster than the primary response. [1 mark]
- Cue. Memory cells made during the first exposure recognise the antigen immediately and rapidly produce lymphocytes and antibodies.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher 20184 marksDescribe the roles of B lymphocytes and T lymphocytes in the specific immune response.Show worked answer →
A 4-mark answer needs the distinct roles of the two lymphocyte types.
B lymphocytes produce antibodies. Each B lymphocyte is specific to one antigen; when it is activated it multiplies and produces large numbers of antibodies that are specific to the antigen on the pathogen. The antibodies bind to the antigens, inactivating the pathogen and marking it for destruction.
T lymphocytes destroy infected body cells. They recognise the antigens displayed on cells that have been infected and induce those cells to die (apoptosis), removing the site where the pathogen is reproducing.
Award (1) B lymphocytes produce antibodies specific to the antigen, (2) antibodies bind antigens to inactivate the pathogen, (3) T lymphocytes recognise infected cells, and (4) T lymphocytes destroy infected cells by inducing cell death.
SQA Higher 20214 marksExplain how immunological memory leads to a faster, stronger response on a second exposure to the same antigen, and state what an autoimmune disease is.Show worked answer →
This is a 4-mark question on memory cells plus a definition.
On the first exposure to an antigen, the selected lymphocytes multiply (clonal selection) and some become memory cells that survive long after the infection has cleared.
On a second exposure to the same antigen, these memory cells recognise it immediately and rapidly produce a large number of the correct lymphocytes and antibodies. This secondary response is faster and stronger than the first, so the pathogen is destroyed before it can cause illness.
An autoimmune disease is one in which the immune system mistakenly attacks the body's own cells, because it fails to recognise them as self. Award (1) first exposure produces memory cells, (2) memory cells survive long term, (3) second exposure gives a faster, stronger secondary response, and (4) autoimmune disease defined as the immune system attacking self.
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