cells and immune system C Flashcards
what is an antigen
-molecule that can generate an immune response when detected by the body
-proteins which are found on the surface of cells
What types of cells and molecules can the immune system identify?
- Pathogens (disease causing microorganisms) eg. viruses, fungi, bacteria
- Cells from other organisms of the same species (eg. organ transplants)
- Abnormal body cells eg. tumour cells or virus-infected cells
- Toxins (poisons) released by some bacteria
How are cells identified by the immune system?
-Each type of cell has specific molecules on its surface (cell-surface membrane / cell wall) that identify it
-Often proteins → have a specific tertiary structure (or glycoproteins / glycolipids)
what are phagocytes
a type of white blood cell
describe how pathogens are destroyed by phagocytosis
1.Phagocyte attracted by chemicals / recognises (foreign) antigens on pathogen
2 Phagocyte engulfs pathogen by surrounding it with its cell membrane
3 Pathogen contained in vesicle / phagosome in cytoplasm of phagocyte
4 Lysosome fuses with phagosome and releases lysozymes (hydrolytic enzymes)
5 Lysozymes hydrolyse / digest pathogen
what do T lymphocytes recognise
antigen presenting cells eg. infected cells, phagocytes presenting antigens, transplanted cells, tumour cells etc
Describe the response of T lymphocytes to a foreign antigen (the cellular response)
1.T lymphocytes recognises antigen presenting cells after phagocytosis
2. Specific T helper cell with receptor complementary to specific antigen binds to it, becoming activated and dividing rapidly by mitosis to form clones which:
- Stimulate B cells for the humoral response
-Stimulate cytotoxic T cells to kill infected cells / tumor cells
- Stimulate phagocytes to engulf pathogens by phagocytosis
what do B lymphocytes recognise
free antigens eg. in blood or tissues, not just antigen presenting cells
Describe the response of B lymphocytes to a foreign antigen (the humoral response)
- Clonal selection:
-Specific B lymphocyte with complementary receptor (antibody on cell surface) binds to antigen
-This is then stimulated by helper T cells (which releases cytokines)
- So divides (rapidly) by mitosis to form clones - Some differentiate into B plasma cells → secrete large amounts of (monoclonal) antibody
- Some differentiate into B memory cells → remain in blood for secondary immune response
what are antibodies
-Quaternary structure proteins (4 polypeptide chains)
-Secreted by B lymphocytes eg. plasma cells in response to specific antigens
-Bind specifically to antigens forming antigen-antibody complexes
state the structure of an antibody
-heavy polypeptide chains
-hinge region
-light polypeptide chains
-disulfide bridge
-variable region
-antigen binding site
-constant region
Explain how antibodies lead to the destruction of pathogens
-Antibodies bind to antigens on pathogens forming an antigen-antibody complex
=Specific tertiary structure so binding site / variable region binds to complementary antigen
-Each antibody binds to 2 pathogens at a time causing agglutination (clumping) of pathogens
-Antibodies attract phagocytes
-Phagocytes bind to the antibodies and phagocytose many pathogens at once
explain the differences between primary and secondary immune response
PRIMARY - first exposure to antigen
=Antibodies produced slowly & at a lower conc.
=Takes time for specific B plasma cells to be stimulated to produce specific antibodies
= Memory cells produced
SECONDARY - second exposure to antigen
=Antibodies produced faster & at a higher conc.
=B memory cells rapidly undergo mitosis to produce many plasma cells which produce specific antibodies
what is a vaccine
-Injection of antigens from attenuated (dead or weakened) pathogens
-Stimulating formation of memory cells
Explain how vaccines provide protection to individuals against disease
- Specific B lymphocyte with complementary receptor binds to antigen
- Specific T helper cell binds to antigen-presenting cell and stimulates B cell
- B lymphocyte divides by mitosis to form clones
- Some differentiate into B plasma cells which release antibodies
- Some differentiate into B memory cells
- On secondary exposure to antigen, B memory cells rapidly divide by mitosis to produce B plasma cells
- These release antibodies faster and at a higher concentration
Explain how vaccines provide protections for populations against disease
-Herd immunity - large proportion of population vaccinated, reducing spread of pathogen
=Large proportion of population immune so do not become ill from infection
=Fewer infected people to pass pathogen on / unvaccinated people less likely to come in contact with someone with disease
describe the difference between active and passive immunity
ACTIVE IMMUNITY
=Initial exposure to antigen eg. vaccine or primary infection
=Memory cells involved
=Antibody produced and secreted by B plasma cells
=Slow; takes longer to develop
=Long term immunity as antibody can be produced in response to a specific antigen again
PASSIVE IMMUNITY
=No exposure to antigen
=No exposure to antigen
=Antibody introduced from another organism eg. breast milk / across placenta from mother
=Faster acting
=Short term immunity as antibody hydrolysed (endo/exo/dipeptidases)
Explain the effect of antigen variability on disease and disease prevention
-Antigens on pathogens change shape / tertiary structure due to gene mutations (creating new strains)
-So no longer immune (from vaccine or prior infection)
=B memory cell receptors cannot bind to changed antigen on secondary exposure
=Specific antibodies not complementary to changed antigen
describe the structure of a HIV particle
-lipid envelope-> the outer layer
-RNA-> the genetic material
-reverse transcriptase-> enzyme which converts RNA into single stranded DNA
-capsid-> surrounds core of the virus
-attachment protein-> bind to receptors on the host cells
Describe the replication of HIV in helper T cells
- HIV attachment proteins attach to receptors on helper T cell
- Lipid envelope fuses with cell-surface membrane, releasing capsid into cell
- Capsid uncoats, releasing RNA and reverse transcriptase
- Reverse transcriptase converts viral RNA to DNA
- Viral DNA inserted into helper T cell DNA (may remain latent)
- Viral protein / capsid / enzymes are produced
a. DNA transcribed into HIV mRNA
b. HIV mRNA translated into new HIV proteins - Virus particles assembled and released from cell (via budding)
Explain how HIV causes the symptoms of acquired immune deficiency
syndrome (AIDS)
-HIV infects and kills helper T cells (host cell) as it multiplies rapidly
=So T helper cells can’t stimulate cytotoxic T cells, B cells and phagocytes
= So B plasma cells can’t release as many antibodies for agglutination & destruction of pathogens
-Immune system deteriorates → more susceptible to (opportunistic) infections
-Pathogens reproduce, release toxins and damage cells
Explain why antibiotics are ineffective against viruses
-Viruses do not have metabolic processes (eg. do not make protein) / ribosomes
-Viruses do not have bacterial enzymes / murein cell wall
What is a monoclonal antibody?
-Antibody produced from genetically identical / cloned B lymphocytes / plasma cells
-So have same tertiary structure
Explain how monoclonal antibodies can be used in medical treatments
-Monoclonal antibody has a specific tertiary structure / binding site / variable region
-Complementary to receptor / protein / antigen found only on a specific cell type (eg. cancer cell)
- Therapeutic drug attached to antibody
- Antibody binds to specific cell, forming antigen-antibody complex, delivering drug
how does agglutination of pathogens happen
-an antibody has two antigen binding sites
-pathogens are clumped together and phagocytes are attracted
- clumps of pathogens are destroyed by the phagocytes
Explain how monoclonal antibodies can be used in medical diagnosis
-Monoclonal antibody has a specific tertiary structure / binding site / variable region
-Complementary to specific receptor / protein / antigen associated with diagnosis
-Dye / stain / fluorescent marker attached to antibody
- Antibody binds to receptor / protein / antigen, forming antigen-antibody complex
Explain the use of antibodies in the ELISA test to detect antigens
- Attach specific monoclonal antibodies to well
- Add sample with potential antigens, then wash well
- Add complementary monoclonal antibodies with enzymes attached → bind to antigens if present
- Wash well → remove unbound antibodies (to prevent false positive)
- Add substrate → enzymes create products that cause a colour change (positive result)
Suggest the purpose of a control well in the ELISA test
-Compare to test to show only enzyme causes colour change
-Compare to test to show all unbound antibodies have been washed away
Discuss some general ethical issues associated with the use of vaccines and monoclonal antibodies
-Pre-clinical testing on / use of animals - potential stress / harm / mistreatment
=But animals not killed & helps produce new drugs to reduce human suffering
-Clinical trials on humans - potential harm / side-effects
-Vaccines - may continue high risk activities and still develop / pass on pathogen
-Use of drug - potentially dangerous side effects
