The Humoral Response
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of the cellular response. You can test your knowledge on this below.
What type of cells do T-cells interact with during the immune response?
T cells interact with antigen-presenting cells (APCs) such as phagocytes, cancer cells and infected body cells. T-helper cells alse activate B-cells.
How do cytotoxic T-cells kill infected cells?
Cytotoxic T-cells release perforins, which create pores in the infected cell’s membrane, causing lysis and cell death.
What is the role of T-helper cells in the immune response?
T-helper cells stimulate B cells to divide. They also secrete cytokines, which help stimulate further phagocytosis.
Topic Explainer Videos
Check out this @LauraDoesBiology video that explains the humoral response or read the full notes below. Once you've gone through the whole note, try out the practice questions!
The Humoral Response (B-Cell Response)
What is the Humoral Response?
- The humoral response involves B-cells and the production of antibodies by plasma cells.
- It is part of the specific immune response, which is antigen-specific and provides long-term immunity.
Stages of the Humoral Response
Activation of B-Cells (Clonal Selection)
- B-cells have specific antibodies acting as receptors on their surface.
- When a B-cell receptor binds to a complementary antigen, the B-cell takes in the antigen and presents it on its surface.
- T-helper cells bind to the antigen-presenting B-cell and release cytokines, activating the B-cell.
Clonal Expansion (B-Cell Proliferation and Differentiation)
- Activated B-cells undergo mitosis, producing many identical B-cells. This can also be called clonal expansion.
- These differentiate into two types of cells:
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Plasma Cells: Secrete large amounts of antibodies into the blood.
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Memory B Cells: Provide long-term immunity by responding quickly if the same pathogen is encountered again.
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Antibody Production and Action
- Plasma cells secrete specific antibodies, which bind to the pathogen’s antigen.
- Antibodies act in the following ways:
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Agglutination: Pathogens are clumped together, making it easier for phagocytes to engulf them.
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Opsonisation: Antibodies coat the pathogen, marking it for destruction by phagocytes.
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Neutralisation: Antibodies bind to and neutralise toxins. They also bind to viral proteins, stopping viruses from entering and infecting body cells.
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Immunological Memory
- Memory B-cells remain in the blood after infection.
- If the same pathogen is encountered again, memory B-cells rapidly divide into plasma cells, producing antibodies much faster.
- This is called the secondary immune response, which is faster and stronger than the primary response.
Key Terms
- B-Cells: A type of white blood cell involved in the humoral response.
- Antibody (immunoglobulin): A Y-shaped protein produced by a plasma cell that binds specifically to an antigen.
- Clonal Selection: The process by which a B-cell with the correct antibody is selected and activated.
- Plasma Cell: A differentiated B-cell that produces and secretes antibodies.
- Memory B-Cell: A long-lived B-cell that remains in circulation for faster future immune responses.
- Agglutination: The clumping together of pathogens by antibodies.
- Opsonisation: The process of marking pathogens for destruction by phagocytes.
- Cytokines: Chemical signals released by T-helper cells that stimulate B-cell activation and further phagocytosis.
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Exam Tips
When describing the humoral response in an exam, make sure to clearly differentiate between clonal selection - stimulation of the correct B-cell and clonal expansion - B-cells cloning by mitosis.
Remember, B-cells require stimulation by Helper T-cells.
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Describe how B-lymphocytes are activated and how they respond to a pathogen. (6 marks)
- A B-cell with complementary receptors binds to the pathogen’s antigen.
- The B-cell engulfs the pathogen and presents the antigen on its surface.
- T-helper cells bind to the antigen-presenting B cell and release cytokines, activating the B cell (clonal selection).
- The activated B-cell undergoes mitosis to form many identical B cells (clonal expansion).
- These differentiate into plasma cells, which secrete antibodies
- And memory B-cells, which provide long-term immunity.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!