Cell Recognition and The Immune System
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of cell membrane proteins. You can test your knowledge on this below.
What are extrinsic membrane proteins?
Proteins on the surface of the cell membrane. They span only one side of the phospholipid bilayer.
What are glycoproteins?
Proteins with a carbohydrate group attached to them.
What type of cell makes up the immune system?
White blood cells.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains cell recognition and the immune system or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Cell Recognition and Antigens
- The immune system differentiates between self and non-self cells using antigens present on cell surfaces.
- Antigens could be proteins, glycoproteins or glycolipids. The combination of antigens on the cell surface is unique.
- Each cell has unique antigens that allow the immune system to recognise whether a cell is part of the body or a foreign invader.
- Pathogens, abnormal body cells (e.g., cancer cells) and cells from other organisms (e.g., organ transplants) can all be identified as foreign due to their antigens.
Self vs. Non-Self Antigens
Self-Antigens:
- Present on normal body cells.
- Recognised as harmless by the immune system.
- Failure to recognise self-antigens correctly can result in autoimmune diseases (e.g., multiple sclerosis).
Non-Self Antigens:
- Found on pathogens, transplanted cells, or abnormal cells (e.g., cancer cells).
- Recognised as foreign, triggering an immune response.
- They include bacterial surface proteins, viral coat proteins, and toxins.
Antigenic Variability
Some pathogens, like influenza viruses and HIV, change their surface antigens through mutations.
This means:
- Memory cells from a previous infection may no longer recognise the pathogen.
- Vaccines may need frequent updates, as seen with the flu vaccine.
- Recurrent infections are common, e.g., the common cold and malaria.
The Role of Antigens in The Immune Response
Detection of Foreign Cells
- When a pathogen enters the body, its antigens are detected as foreign by white blood cells.
- This triggers an immune response to eliminate the threat.
Phagocytosis and Antigen Presentation
- Phagocytes engulf pathogens and digest them.
- The pathogen's antigens are displayed on the phagocyte's surface. (The phagocyte becomes an antigen presenting cell).
Activation of the Immune Response
- T-lymphocytes (T-cells) bind to the presented antigens and stimulate:
-
-
-
Cytotoxic T-cells to kill infected cells.
-
Helper T-cells to activate B-cells.
-
-
- B-lymphocytes (B-cells) bind to antigens and produce specific antibodies.
Antibodies and Memory Cells
- Antibodies neutralise pathogens by binding to their antigens.
- Memory B and T-cells remain in circulation, allowing a faster secondary immune response if the same antigen is encountered again.
Read more about the immune respinse and the specific role of B-cells and T-cells in the next few study notes!
Key Terms
- Antigen: A molecule, usually a protein, that triggers an immune response.
- Phagocyte: A white blood cell that engulfs and digests pathogens.
- T-cells: Lymphocytes that coordinate the immune response and kill infected cells.
- B-cells: Lymphocytes that produce antibodies.
- Memory cells: Cells that remain after infection to provide long-term immunity.
No answer provided.
Exam Tips
Clearly distinguish between self-antigens (on body cells) and non-self antigens (from pathogens or transplants).
When discussing immune response, specify whether T-cells or B-cells are involved.
Use the correct terminology: antigens trigger an immune response, while antibodies are produced by B-lymphocytes, called plasma cells, and bind to foreign antigens.
No answer provided.
Describe how the structure of an antigen enables it to be recognised by the immune system. (2 marks)
- Antigens have a specific shape that is complementary to antibodies or T-cell receptors.
- The immune system recognises non-self antigens as foreign, triggering an immune response.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!