The Immune System Flashcards
What are antigens?
Antigens are molecules (usually proteins) that can generate an immune response when detected by the body
Where are antibodies usually found?
They are usually found on the surface of cells and are used by the immune system to identify: pathogens, abnormal body cells, toxins and cells from other individuals of the same species
What are the four main stages of the immune response?
- Phagocytes engulf pathogens
- Phagocytes activate T-cells
- T-cells activate B-cells, which divide into plasma cells
- Plasma cells make more antibodies to a specific antigen
What is a phagocyte?
A phagocyte is a type of white blood cell that carries out phagocytosis. They’re found in blood and in tissues and are the first cells to trigger an immune response
Explain the process of phagocytosis
- A phagocyte recognises the foreign antigens on a pathogen
- The cytoplasm of the phagocyte moves round the pathogen, engulfing it
- The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte
- A lysosome fuses with the phagocytic capsule. The lysozyme break down the pathogen
- The phagocyte then presents the pathogens antigens - it sticks the antigens on its surface to activate other immune system cells
What is a T-cell?
A T-cell is a type of white blood cell
How do phagocytes activate T-cells?
T-cells have receptor proteins on their surface that bind to complimentary antigens presented to it by phagocytes. This activate the T-cell
Do different types of T-cells respond the same way?
Different types of T-cell respond in different ways. Helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells which kill abnormal and foreign cells. Helper T-cells also activate B-cells which secrete antibodies
What are B-cells?
B-cells (B-lymphocytes) are a type of white blood cell. They’re covered with antibodies - proteins that bind antigens to form and antigen-antibody complex. Each B-cell has a different shaped antibody on it’s membrane, so different ones bind to different shaped antigens
What happens when B-cells are activated?
When the antibody on the surface of a B-cell meets a complimentary shaped antigen, it binds to it. This, together with substances released from T-helper cells, activates the B-cell. This process is called clonal selection. The activated B-cell divides into plasma cells
What are plasma cells?
Plasma cells are identical to B-cells (they’re clones)
What do plasma cells secrete?
Plasmas cells secrete lots of antibodies specific to the antigen. These are called monoclonal antibodies. They bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes
What happens when plasma cells make antibodies?
Antibodies have two binding sites, so they can bind to two pathogens at the same time. This means that pathogens become clumped together - this is called agglutination. Phagocytes then bind to the antibodies and phagocytose many pathogens at once. This process leads to the destruction of pathogens carrying this antigen in the body
What are antibodies?
Antibodies are proteins - they’re made up of chains of amino acids
What does the specificity of an antibody depend on?
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 complimentary to one specific antigen
Antibodies all have the same what?
All antibodies have the same constant regions
The immune response can be split into what?
- The cellular response
2. The humoral response
What parts of the immune response make up the cellular response?
The T-cells and other immune system cells that they interact with, e.g. phagocytes, form the cellular response
What parts of the immune response make up the humoral response?
B-cells, clonal selection and the production of monoclonal antibodies form the humoral response
What is the primary immune response
When an antigen enters the body for the first time it activates the immune response. This is the primary response
Is the primary response fast or slow?
The primary response is slow - there aren’t many B-cells that can make the right antibody to bind to the antigen. Eventually, the body will produce enough of the right antibody to overcome the infection - meanwhile the infected person will show symptoms of the disease
In the primary response when is a person immune?
After being exposed to the antigen, both T-cells and B-cells produce memory cells which remain in the body for a long time. Memory T-cells remember the specific antigen and will recognise it. Memory B-cells record the specific antibodies needed to bind to the antigen. The person is now immune - their immune system has the ability to respond quickly to a second infection
What happens in the secondary immune response?
If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response. Clonal selection happens faster. Memory B-cells are activated and divide into plasma cells to produce the right antibody to the antigen. Memory T-cells are activated and divide into the right type of T-cell to kill the cell carrying the antigen. The secondary repose often gets rid of the pathogen before you begin to show any symptoms
