Why does the immune system not normally attack the body's own tissues?

During development any lymphocyte whose receptor happens to fit a self antigen is destroyed or permanently switched off, so the lymphocytes that survive into circulation react only to foreign material.

Explain what is meant by clonal selection.

The body already carries an enormous variety of lymphocytes, each with a receptor of one shape, and an antigen entering the body activates only the few whose receptors are complementary to it.

What is clonal expansion?

Clonal expansion is the repeated division by mitosis of the selected lymphocyte, producing a large clone of genetically identical cells all specific to the same antigen.

Into which two kinds of cell does an activated B lymphocyte develop?

It develops into plasma cells, which secrete antibody, and into B memory cells, which remain in circulation.

Eduqas A-Level Biology A400QS

Biological Molecules

Topic overview Inorganic ions and the properties of water Monosaccharides and disaccharides Polysaccharides, storage and structure Lipids, triglycerides and phospholipids Amino acids and protein structure Condensation, hydrolysis and the food tests

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Immunology and Disease: The Immune Response

Antigens, B lymphocytes and the humoral response

3 things to know
Component 3

Overview

Self antigens and non-self antigens, what is meant by clonal selection and clonal expansion.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is meant by self antigens and non-self antigens?

Key term

Why is the primary response to an antigen slow and small?

Key term

Where are B lymphocytes made, and where do they mature?

Questions from this subtopic

Each one with the model answer underneath.

1
Where are B lymphocytes made, and where do they mature?
Model answer
B lymphocytes are both made and matured in the bone marrow.
2
What is meant by self antigens and non-self antigens?
Model answer
Self antigens are the molecules on the surfaces of the body's own cells, which the immune system tolerates, while non-self antigens are foreign molecules that provoke a specific immune response.
3
Why does the immune system not normally attack the body's own tissues?
Model answer
During development any lymphocyte whose receptor happens to fit a self antigen is destroyed or permanently switched off, so the lymphocytes that survive into circulation react only to foreign material.
4
Explain what is meant by clonal selection.
Model answer
The body already carries an enormous variety of lymphocytes, each with a receptor of one shape, and an antigen entering the body activates only the few whose receptors are complementary to it.
5
What is clonal expansion?
Model answer
Clonal expansion is the repeated division by mitosis of the selected lymphocyte, producing a large clone of genetically identical cells all specific to the same antigen.
6
Into which two kinds of cell does an activated B lymphocyte develop?
Model answer
It develops into plasma cells, which secrete antibody, and into B memory cells, which remain in circulation.

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