Cells: Cell Recognition & the Immune System - Lymphocytes Flashcards
What are lymphocytes?
- Lymphocytes are a type of white blood cell
- They are part of the specific response to antigens
- There are two types:
- T-lymphocytes (T-cells)
- B-lymphocytes (B-cells)
How are T-cells activated?
- T-cells have receptor proteins on its surface
- These proteins bind to complementary antigens on antigen-presenting cells
- This causes the T cell to divide rapidly by mitosis - clonal expansion
- These cloned T cells can then differentiate into different specialised T cells
What are the different types of specialised T-cells?
• Cytotoxic T-cells
- Kill/destroy cells presenting abnormal and foreign antigens
• Helper T-cells
- Activate and stimulate phagocytes, cytotoxic T-cells and B-cells
How are B-cells activated?
- B-cells are covered with antibodies
- Each B-cell has a different shaped antibody on its membrane, so different ones bind to different shaped antigens
- When the antibody on a B-cell meets a complementary antigen, it binds to it
- This, together with substances released from T-cells, activate the B-cell
- This process is called clonal selection
- The activated B-cell divides into plasma cells
What are plasma cells?
- Plasma cells are clones of B-cells that produce antibodies specific to the antigen
- These are called monoclonal antibodies
How do monoclonal antibodies help destroy pathogens?
- The monoclonal antibodies bind to the antigens of pathogens to form antigen-antibody complexes
- Antibodies have two binding sites, so can bind to two pathogens at a time
- This causes the pathogens to clump together - this is called agglutination
- Phagocytes then bind to the antibodies and then phagocytose many pathogens at once
What is an antibody?
-A protein found in the blood that is produced by plasma cells which binds to antigens as a part of the immune response
Describe the structure of an antibody
- Antibodies are proteins - made up of chains of amino acids
- The specificity of an antibody depends on its variable regions, which form the antigen binding sites
- Each antibody has a variable region with a unique tertiary structure that’s complementary to one specific antigen
- All antibodies have the same constant regions
Describe the two types of immune responses
• Cellular response
- Includes T-cells and other immune system cells that they interact with (e.g phagocytes)
• Humoral response
- Includes B-cells, clonal selection and the production of monoclonal antibodies
Describe the primary immune response
- The primary response is when an antigen enters the body for the first time and activates the immune system
- The primary response is slow because there aren’t many B-cells that can make complementary antibodies
- Eventually the body will produce enough of the antibody to overcome the infection
- Meanwhile the infected person will show symptoms of the disease
- After exposure to an antigen, both T and B cells produce memory cells
- Memory T-cells remember the specific antigen and will recognise it later
- Memory B-cells record the specific antibodies needed to bind to the antigen
- The person is now immune and has the ability to respond quickly to a second infection
Describe the secondary immune response
- The secondary response is when the same pathogen enters the body again - the immune system will produce a quicker, stronger immune response
- Clonal selection happens faster
- Memory B-cells activate and divide into plasma cells that produce complementary antibodies
- Memory T-cells activate and divide into the correct type of T-cells to kill the APC
- The secondary response often gets rid of the pathogen before you begin to show any symptoms
What is clonal selection?
- Clonal selection is the process of matching the antigens on antigen presenting cells with the antigen receptors on B and T lymphocytes
What is clonal expansion?
- The production of many genetically identical daughter cells through cell division of the activated B or T lymphocyte after clonal selection
