5 - Cell recognition and the immune system Flashcards
What are the two kinds of specific immune responses?
Cell mediated response (T lymphocytes)
Humoral response (B lymphocytes)
Describe the process of phagocytosis (5)
Phagocyte attracted to pathogen by pathogen’s chemical products
Phagocyte attaches by receptors to pathogen
Phagosome forms around pathogen
Lysosomes release hydrolytic lysozymes into phagosome, which hydrolyse pathogen
Hydrolysis products are absorbed by phagocyte, the antigens are displayed on its surface
What is an antigen?
A molecule, usually a protein, that triggers an immune response by lymphocytes (production of antibodies)
Where do T lymphocytes mature?
Thymus gland
What do T cells respond to?
Specific antigens presented on body cells included phagocytic cells, infected viral cells and cancer cells.
Describe the cellular response. (4)
Pathogens invade body cells, or taken in by phagocytes.
Phagocyte places pathogen antigens on cell surface membrane.
Receptors on a T(H) cell fit onto these antigens.
T cell divides rapidly mitosis to form a clone of genetically identical cells.
Give 4 examples of molecules the immune system can identify.
This is from the exam specification.
- Pathogens
- Cells from other organisms of the same species
- Abnormal body cells
- Toxins
Why are pathogens such as the flu and cold difficult for immune systems to defend against?
Their antigens can change.
Give two types of lymphocytes.
B, T
Give two kinds of T lymphocytes.
Helper
Cytotoxic
Give two kinds of T lymphocytes.
Helper
Cytotoxic
How are helper and cytotoxic T cells formed?
T lymphocyte binds to specific antigen on antigen-presenting-cell.
These T cells undergo rapid mitosis to produce helper and cytotoxic cells.
Give 4 function of Helper T cells. (4)
- Stimulate maturation of B-lymphocytes
- Stimulate increased phagocytosis
- Activate Cytotoxic T cells
- Stimulate production of Memory B cells
How many different antibodies can each type of B cell produce?
1
Where do B cells mature?
Bone marrow
Where are antibodies found in mature B cells?
Cell-surface membrane
When does a B cell undergo clonal selection?
When it binds to a specific antigen and first undergoes mitosis.
What is clonal expansion?
When a B cell has binded to an antigen and undergoes repeated mitosis
What do B cells divide to form?
- Memory cells
- Plasma cells
What is the function of plasma cells?
High production of antibodies specific to antigen
How long do plasma cells live?
~ 3-4 weeks
How long do memory cells live?
Many years - lifetime
What degree of structure do antibodies have?
Quaternary
Describe the structure of an antibody.
- Y-shaped
- 2 long heavy chains on the inside
- 2 short light chains on the outside
- The chains are joined by disulfide bridges
- Each chain has a variable region (at the top of the Y) and a constant region
Why is an antibody specific to only one type of antigen?
Variable region is made from amino acids which is complementary to antibody shape
Define agglutination.
The clumping of pathogens due to the multiple antigen-binding sites of antibodies.
Give three function of antibodies.
- Neutralise pathogens
- Act as marker to attract phagocytes to pathogens
- Agglutination
What is a primary immune response?
Response to a newly encountered antigen
Give the name for a response to a previously encountered antigen.
Secondary immune response.
Describe a secondary immune response.
Memory cell binds to pathogen
Quickly divides to produce plasma cells and memory cells
This is a very fast process compared to a primary immune response.
Give two types of vaccine.
Inactive/dead
Weakened/alive
What type of immunity are vaccines?
Artificial, active
How do vaccines cause long-term immunity?
Stimulate production of memory cells
Do weakened or dead vaccines produce a stronger, longer-lasting response?
Weakened
What is herd immunity?
When a sufficiently large proportion of a population has been vaccinated and is immune, that it is difficult for a pathogen to spread within the population.
Suggest one reason a pathogen may not have been eradicated in a region, despite the presence if a vaccine.
Lack of public health facility ie too few trained personnel able to administer vaccine
Give an example of a natural passive immunity.
Transmission of antibodies across the placenta from mothers to foetuses
Are memory cells produced in active immunity, passive immunity, or both?
Active immunity
What kind of virus is HIV?
Retrovirus
Describe the structure of an HIV particle.
5 components
- 2 RNA strands
- Proteins ie reverse transcriptase
- Capsid
- Viral envelope
- Attachment proteins
How does HIV replicate?
Begin at entering of bloodstream by HIV particles.
- HIV enteres bloodstream
- Viral RNA enters helper T cell
- Viral reverse transcriptase coverts viral RNA to DNA
- DNA inserted into chromosomes of T cell
- T cell replicates by normal means, producing HIV particle components from DNA
Describe the effect of HIV.
- HIV particles reproduced and spread between T cells
- Helper T cells die
- B cells no longer activated
- No antibodies produced
- AIDS developed
When is an individual said to have AIDS?
When antibodies are no longer produced.
Why are antibiotics ineffective against viruses?
Viruses are non-living, therefore they have no cell structure or metabolism which can be disrupted.
Give two common ways in which antibiotics act.
- Prevent protein synthesis
- Disrupt metabolism of cell.
Give two uses of monoclonal antibodies.
- Medical diagnosis
- Targeting medication to specific cell types by attaching a therapeutic drug to an antibody
Give one reason some people find the use of monoclonal antibodies unethical.
Tested on animals
What is ELISA?
A diagnostic test using antibodies.
What does ELISA stand for?
Enzyme-linked-immunosorbent assay
Describe the use of an indirect ELISA test for HIV.
- HIV antigens bound to bottom of reaction vessel
- Blood sample added to vessel
- HIV-specific antibodies bind to antigens (primary antibodies)
- Vessel is washed to remove other antibodies in blood
- Secondary antibody specific to primary antibody added to vessel. It has an enzyme attached.
- If primary antibodies are present, secondary antibodies bind to them
- Rewash to remove excess secondary antibodies
- Substrate is added
- If HIV antibodies were present in blood, enzyme on secondary antibodies will react with substrate to change the solution’s colour
What is an indirect ELISA test?
A test using two lots of antibodies.
