The Cellular Response
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of phagocytosis. You can test your knowledge on this below.
What are antigens?
Molecules (usually proteins) on the surface of cells/ pathogens. Foreign antigens on the surface of a pathogen trigger an immune response.
What are the 2 main types of phagocyte?
- Macrophage
- Neutrophil
What is the role of lysosomes in phagocytosis?
To fuse with the phagocytic vacuole (the phagosome) and release lysozymes to digest the pathogen.
Topic Explainer Videos
Check out this @JoeDoesBiology video that explains cellular response or read the full notes below. Once you've gone through the whole note, try out the practice questions!
If you want an explainer of specific immune response, check out this video from @LauraDoesBiology and once you've gone through the whole note, try out the practice questions!
The Cellular Response Overview
- The cellular (T-lymphocyte) response is part of the specific immune system.
- The specific immune response is antigen-specific and provides long-term immunity.
- T-lymphocytes respond to antigen presenting cells. These may be phagocytes, cancerous cells, transplanted cells or cells infected with a virus.
Stages Of The Cellular Response
Pathogen Invasion & Antigen Presentation
- A phagocyte (e.g., macrophage) engulfs a pathogen and hydrolyses/ digests it.
- It presents antigens from the pathogen on its surface, becoming an antigen-presenting cell (APC).
Activation of T-Lymphocytes
- T-helper cells have different and specific T-cell receptors that bind to the antigen on the APC.
- This activates the T-helper cell. We say the T-helper cell has undergone clonal selection.
Clonal Expansion & Differentiation
- Activated T-helper cells divide by mitosis, this can be called clonal expansion.
- They then differentiate forming:
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More T-helper cells.
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Memory T-cells which play a role in the secondary immune response for long-term immunity.
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Cytotoxic T-cells (Killer T-cells) to directly kill infected cells.
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Action of Cytotoxic T Cells (Killer T cells)
- Cytotoxic T-cells release perforins, which create pores in the membrane of infected cells.
- This causes cell lysis, killing the infected cell and preventing viral replication.
Why Is The Cellular Response Important?
- Targets viruses, which hide inside host cells, making them inaccessible to antibodies.
- Essential for destroying cancer cells.
- Forms long-term immunity via memory T-cells.
- T-helper cells are needed to activate B-cells in the humoral response.
- T-helper cells release cytokines (chemical signals) to stimulate further phagocytosis.
Key Terms
- Antigen-presenting cell (APC): A cell that displays foreign antigens on its surface.
- T-helper cells (TH cells): Release cytokines to activate other immune cells.
- Cytotoxic T-cells (TC cells): Kill infected cells using perforins.
- Cytokines: Chemical signals that coordinate immune responses.
- Perforin: A protein that creates pores in the target cell membrane.
- Clonal expansion: Rapid mitotic division of T-cells.
- Memory T-cells: Provide long-term immunity.
No answer provided.
Describe the role of T-lymphocytes in the immune response. (6 marks)
- Phagocytes engulf pathogens and present antigens on their surface.
- T-helper cells bind to the antigen on the antigen-presenting cell (APC) and become activated.
- These activated T-helper cells divide by mitosis or undergo clonal expansion.
- Some differentiate into cytotoxic T cells, which release perforins, creating pores in infected cell membranes and killing them.
- Some differentiate into memory T cells, providing long-term immunity.
- Some differentiate into T-helper cells which activate B-cells
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!