The Immune System Flashcards
What are antigens?
Molecules that generate an immune response when detected by the body
Where are antigens usually found?
On the surface of cells that 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 4 main stages of the immune response?
- Phagocytes engulf pathogen
- Phagocytes activate T-cell
- T-cell activate B-cells, which divide into plasma cells
- Plasma cells make more antibodies to a specific antigen
Explain the first stage of the immune response - phagocyte engulfs pathogen
A phagocyte recognises the foreign antigens on a pathogen. The cytoplasm of the phagocyte moves around the pathogen, engulfing it, containing the pathogen in a phagocytic vacuole. A lysosome fuses with the phagocytic vacuole and lysozyme break down the pathogen. The phagocyte presents the pathogen’s antigens to activate other immune cells
What is a phagocyte?
A type of white blood cell that carries out phagocytosis
Explain the second stage in the immune response - phagocytes activate T-cells
A T-cell is a white blood cell - it has receptor proteins on its surface that bind to complimentary antigens presented by phagocytes, this activates it. Helper T-cells release chemical signals that activate phagocytes and cytotoxic T-cells, which kill abnormal cell. Helper T-cells also activate B-cells, which secrete antibodies
Explain the third stage in the immune response - T-cells activate B-cells
When the antibody on the surface of a B-cell meets a complimentary shape antigen, it binds to it. This, together with substances released from helper T-cells, activates the B-cell. This is clonal selection. The activated B-cell divides into plasma cells
What is a B-cell?
A type of white blood cell that’s covered in antibodies. Each B-cell has a different shaped antibody on its membrane, so different ones bind to different shaped antigens
Whats an antibody?
A protein that binds to antigens to form an antigen-antibody complex
Explain the fourth stage in the immune response - plasma cells make more antibodies
Plasma cells secret monoclonal antibodies that bind to the antigen on the surface of the pathogen to form an antibody-antigen complex. Antibodies have two binding sites, so binds to two pathogens at a time - pathogens become clumped together (agglutination). Phagocytes bind to the antibody and phagocytose may pathogens at once
What is the structure of an antibody?
They are proteins, made up of chains of amino acids. The specificity depends on its variable regions, which form the antigen binding sites. The variable region has a unique tertiary structure that’s complimentary to a specific antigen. All antibodies have constant regions
The immune spouse can be split into two things, what are they?
- Cellular - the T-cells and other immune system cells the interact with
- Humoral - B-cells, clonal selection and the production of monoclonal antibodies
Explain the primary immune response
When an antigen enters the body for the first time it activates the immune system. Response is slow because there aren’t many B-cells that can make antibodies for the antigen. Eventually the body will produce enough antibodies to overcome the disease, meanwhile the infected person will show symptoms. After being exposed to the antigen B-cells and T-cells produce memory cells that will recognise the antigen, and produce the correct antibody, if infected again. The person is now immune
What are memory cells?
Both T-cells and B-cells produce memory cells. They remain in the body for a long time. Memory T-cells remember the specific antigen and will recognise it a second time. Memory B-cells record the specific antibodies needed to bind to the antigen
Explain the secondary immune response
If the same pathogen enters the body again, the immune system will produce a quicker, stronger response. Clonal selection happens faster. Memory B-cells activate and divide into plasma cells that produce the right antibody to the antigen. Memory T-cells are activated and divide into the correct T-cell to kill the cell carrying the antigen. The secondary response often gets rid of the pathogen before you show any symptoms
