Topic 2.3 - Cells and The Imune System Flashcards
Define antigen
- Molecules (usually proteins) that can generate an immune response when detected by the body
- Unique to each cell
Define foreign antigen
Antigens that are not normally found in the body
What three ways does the immune system identify foreign antigens?
- Pathogens
- Abnormal body cells (e.g. cancerous cells)
- Cells from other organisms from the same species
What three places are antigens presented?
- Surface of cells
- Surface of host cells
- Surface of macrophage / phagocyte that has engulfed the pathogen
Define antigen presenting cell
An immune cell (macrophage) that processes and presents antigen on its surface to activate other immune cells
Define antigen variation
- Change of surface antigens of pathogens
- Different antigens formed due to changes in the DNA / RNA of pathogen (mutation)
What are the two types of primary defences?
Give examples
- Physical barriers > skin
> mucus
> reflexes (e.g. sneezing, blinking) - Chemical barriers > sebum (fatty acids on skin)
> tears (contains lysosomes)
> acids in stomach
What are the three types of secondary defences?
- Inflammatory response
- Haemostasis (blood clotting)
- Phagocytosis
What happens during inflammatory response?
- Chemicals are released from the granules of leukocytes
- Made primarily at sites of tissue damage or infection
- Removes damaged tissue components or pathogens, so that body can begin to heal
What happens during haemostasis?
- Seals damaged blood vessels, preventing significant bleeding
- Done by platelets
What happens during phagocytosis?
- Phagocyte recognises foreign antigens of pathogen
- Phagocyte engulfs pathogen
- Phagocytic vesicle forms around the pathogen
- Lysosomes, containing lysozymes (digestive enzymes) fuses with phagocytic vesicle to create a phagolysosome
- Lysozymes hydrolyse / digest the pathogen
- Pathogen’s antigens are presented on the surface of macrophage
Becomes an antigen presenting cell - Digested pathogen is released out of the phagocytes by exocytosis
Define cellular immune response
The immune response that involves the activation of phagocytes and T-cells
Define humeral immune response
The immune response that involves B-cells, clonal selection and production of antibodies
Describe the process of cellular immune response
1) Phagocytosis > macrophage becomes an antigen presenting cell
2) T-cells > Receptor proteins on its surface that bind to complementary antigens presented on the macrophage
> Corrected T-cells are selected and activated
> Th-cells: release chemical signals that activate phagocytes and B-cells which produce antibodies
> Tc-cells: release molecules to kill pathogens, abnormal, infected or foreign cells
Describe the process of humeral immune response
1) B-cells > covered with antibodies
> have complementary antibodies to certain antigens
2) Clonal selection > antibodies on surface of B-cells bind to complementary antigen
3) Clonal expansion > activated B-cells divide by mitosis into plasma cells (clones of B-cells)
4) Antibody production > Plasma cells secrete lots of specific antibodies (monoclonal antibodies)
> antibodies bind to complementary antigen on the pathogen surface to form antigen-antibody complex
> some B-cells differentiate into memory cells
5) Antibodies have two binding sites. This means they can bind to two pathogens at the same time
6) Agglutination > clumping together of pathogens
> Easily engulfed by phagocytes
7) Phagocytes bind to the antibodies and phagocytose many pathogens. It’s leads to destruction of pathogens with the same antigen
Where are T-cells and B-cells developed?
Bone marrow
How fast is the primary response?
Give reasons
- Slow
- Not many B-cells that can make the antibody needed
- Eventually, body will produce enough
- Body will show symptoms of disease
- B-cells produces memory cells
- Person is not immune
How fast is the secondary response?
Give reasons
- Faster
- Antibodies are produced quicker in a higher concentration
- Clonal selection happens faster
- Memory B-cells are activated and divide into plasma cells > produce the correct antibody
- Memory T-cells are activated and divide into correct T-cells > kills cell carrying antigen
- No symptoms as the antigen is gone before symptoms arise
Define immune
Ability to respond quickly to the same antigen
Define cell signalling
Communication between cells
What three things does cell signalling involve?
- Antigens
- Cell surface receptors
- Cytokines (chemical)
Define antibodies
Globular proteins secreted by B-cells in response to the presence of foreign antigens
What is the structure of an antibody?
- Y-shaped
- 4 polypeptide chains held together with a disulphide bridge > quaternary structure
What are the four regions of an antibody?
- Constant region = same in all antibodies
- Variable region = specific to the antibody
= complementary to antigen (has a specific amino acid sequence > primary structure) - Binding site > Tertiary structure
- Hinge region > Allows flexibility and attraction to more than one antigen
