Topic 2---C: Cells and The Immune System- 2. The Immune Response Flashcards
What is a phagocyte?
- It’s a type of white blood cell that carries out phagocytosis.
- They’re found in the blood and in tissue.
- They’re the first cells to respond to an immune system trigger inside the body.
Stages of phagocytosis
- A phagocyte recognises the foreign antigens on a pathogen.
- The pathogen is engulfed into a vesicle called the phagosome.
- Vesicles called lysozymes fuse with the phagosome releasing hydrolytic enzymes which hydrolyse the pathogen.
- End products are expelled from cell (exocytosis).
- Phagocyte becomes an antigen-presenting cell involved in specific immunity.
Stages of humoral response
- Sources of antigens are in the body fluid e.g. toxins, pathogens & antigen-presenting cells.
- B-cell with complementary receptors binds to the antigen.
- T-helper cell activates B-cell to divide by mitosis to form clones (plasma and memory cells).
What is clonal selection?
B-cell with complementary receptor binds to foreign antigens and processes it.
What is clonal expansion?
T-helper cell activates B-cell to divide by mitosis to form clones differentiated into plasma and memory cells.
Stages of cell-mediated response
A:
1. Antigens are presented on the phagocyte.
2. T-helper cells bind to the antigens by there complementary receptors.
3. Signals a chemical that attracts more phagocytes to the area.
B:
1. Infected body cell (consisting of antigens).
2. T-helper cell binds to antigens by their complementary receptors.
3. A signal that releases the cytotoxic t cell which destroys the infected cell.
What is a T-cell?
- Also called a T-lymphocyte.
- It’s another type of white-blood cell.
- It has receptor proteins on it’s surface that bind to complementary antigens presented to it by phagocytes.
Role of T-helper cells
- They activate B-cells to divide by mitosis to produce plasma and memory cells.
- They release chemical signals that attract more phagocytes to the area.
- Signal the cytotoxix t-cell killing the infected cells.
What are B-cells?
- They’re also called B-lymphocytes.
- They’re a type of white blood cell.
- They’re covered with antibodies which is a protein that bind to antigens to form an antigen-antibody complex.
- Each B-cell has a different shaped antibody on it’s membrane, so different ones bind to different shaped antigens.
When will an antibody bind to an antigen?
When the antibody on the surface of a B-cell meets a complementary shaped antigen.
What are plasma cells?
- They’re identical to B-cells (they’re clones).
- They secrete loads of antibodies specific to the antigen.
What is it called when pathogens become clumped together?
Agglutination
What is the structure of an antibody?
- 4x polypeptide chains
- 2x pairs heavy chains and 2x pairs of light chains
- Variable regions (form the antigen binding sites)
- Heavy and light chains held together with disulfide bonds
- It has two binding sites so it can bind to 2 pathogens at the same time
- Constant region is made up of the lower section of the 2 heavy chains forming the receptor binding site.
What is the primary response?
- When an antigen enters the body for the first time so it activates the immune system.
- It’s slow as there aren’t many B-cells that can make the antibody needed to bind to it.
- The infected person will show symptoms of the disease.
- After being exposed to the antigen, both t and b-cells produce memory cells which remain in the body for a long time.
- The person is now immune so the immune system has the ability to respond quickly to a second infection.
What do memory T-cells do?
They remember the specific antigen and will recognise it the second time round.
