2.5 Immunity Flashcards
Name 3 of the body’s defence mechanisms against pathogens.
- non-specific responce: skin barrier, mucus, OR phagocytsosis
- inflammation
- specific immune response
What is an antigen?
A glycoprotein found on the cell-surface membrane that triggers an immune response and identifies a cell as self or non-self.
What is antigenic variability?
When the antigens on the surface of a pathogen change frequently due to genetic mutations.
Why is antigenic variability a problem?
- The surface receptors on lymphocytes and memory cells are complementary in shape to only one antigen.
- When the antigen on a pathogen changes shape the lymphocytes and memory cells can no longer bind
- As a result, there is no secondary immune response
- The host gets re-infected and suffers from the disease again
- previous immunity is no longer effective as memory b cells will have memory of the old antigen shape, so NO LONGER COMPLEMENTARY
What are the two types of phagocytes?
- neutrophils
- macrophages
Describe the process of phagocytosis.
- The pathogens adheres to the phagocyte (Chemotaxis)
- The pathogen binds to the specific receptors on the surface of the phagocyte
3.. The phagocyte engulfs the pathogen (Endocytosis) - Lysosome fuses with the phagosome vesicle
- Lysosomes digest the phagocyte by secreting lysozymes
- Antigens are displayed on the cell surface membrane of APCs
Where do T-lymphocytes mature?
Thymus
Where do B-lymphocytes mature?
Bone Marrow
What are the two types of T-cell?
- T-helper cells
- T-cytotoxic cells
Describe the T-lymphocyte response.
- T-cells have a specific receptor site that binds to the antigens presented on the surface of the phagocyte
- This stimulated the t-cells to divide by mitosis
- The t-cells then differentiate into t-helper cells and t-cytotoxic cells
T-helper cells: involved in the B-lymphocyte response
T-cytotoxic cells: release cytotoxins that destroy the pathogens
- cell mediated response
Describe the B-lymphocyte response.
- B-cells take in antigens by endocytosis and present them on their surface
- Then the t-helper cell binds to these antigens
- This stimulates the b-cells to divide by mitosis (clonal selection)
- This makes b-memory cells and plasma cells
B-memory cells: stimulate a secondary immune response
Plasma cells: produce soluble antibodies specific to the antigen
- humoral response
What is an antibody?
A immunoglobulin specific to an antigen produced by plasma cells in the immune system in response to foreign substances.
Describe the structure of an antibody?
- quaternary structure
- two short chains, two long chains
- each polypeptide chain has a constant and variable region
- binding site on end of variable region
Describe how an antibody-antigen complex is formed.
- antigen and antibody are complementary
- specific binding site on antibody binds to antigen to form and antigen-antibody complex
What is agglutination?
Process in which pathogens get clumped together.
What is a vaccine.
small amounts of weakened/ dead pathogen intentionally put into the body to induce artificial active immunity, where antibodies are secreted by plasma cells.
What are the two types of vaccine?
- live attenuated
- dead/inactivated
What is herd immunity?
Herd immunity arises when a sufficiently large proportion of the population has been vaccinated (and are therefore immune) which reduces the likelihood of the pathogen spreading within that population.
What is active immunity?
- acquired when antigens enter the body
- triggers a specific immune response
- naturally acquired through exposure to pathogens or artificially acquired through vaccines
- produces memory cells for long-term immunity
What is passive immunity?
- acquired without an immune response
- no antibodies produced
- no memory cells
How is HIV transmitted?
- sexual intercourse
- blood transfusions
- mother to child (breast milk)
- mother to child (placenta)
- sharing needles
Describe the structure of HIV.
- two RNA strands
- reverse transcriptase
- capsid
- attachment proteins
- viral envelope (lipid bilayer and glycoproteins)
How does HIV replicate?
- Attachment proteins attach to receptors on helper T cell/lymphocyte
- Nucleic acid/RNA enters cell
- Reverse transcriptase converts RNA to DNA
- Viral protein/capsid/enzymes produced
- Virus particles assembled and released from cell
Describe how HIV replicates once inside helper T cell
- RNA converted into DNA using reverse transcriptase;
- DNA incorporated/inserted into helper T cell
- DNA transcribed into HIV mRNA
- HIV mRNA translated into new HIV/viral proteins for assembly into viral particles
Why can’t antibiotics be used to treat HIV.
Antibiotics are ineffective against viruses as they are non-living.
What are the symptoms of AIDS?
- mild flu-like symptoms
- weakened immune system (HIV destroys helper T-cells which means B-cells can’t be stimulated, therefore antibodies can not be made.)
What are the treatments of HIV?
- antiretroviral therapy
What is a monoclonal antibody.
Antibodies with the same tertiary structure produced from identical plasma cells.
What are the uses of monoclonal antibodies?
- diagnosing HIV, tumours and other pathogens (medical diagnosis)
- pregnancy tests
- detecting blood clots
- can be attached to therapeutic drugs
What are some ethical issues associated with vaccines and mAbs?
- use of animals (testing deemed to be unethical)
Describe the role of antibodies in producing a positive result in an ELISA test
- First antibody is complementary in shape to antigen so binds
- Second antibody with enzyme attached is added
- Second antibody attaches to antigen (direct ELISA test)
OR attaches to first antibody (indirect ELISA test) - Substrate added and colour changes (+ve)
