cell recognition +immune system Flashcards
cells topic (37 cards)
What is an antigen?
● Foreign molecule / protein / glycoprotein / glycolipid
● That stimulates an immune response leading to production of antibody
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 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
- injected antigens e.g. vaccines
- our own cells if autoimmune
Describe phagocytosis of pathogens (non-specific immune response)
- Phagocyte attracted by chemicals / recognises (foreign) antigens on pathogen
2.Phagocyte engulfs pathogen by surrounding it with its cell membrane - Pathogen contained in vesicle / phagosome in cytoplasm of phagocyte
- Lysosome fuses with phagosome and releases lysozymes (hydrolytic enzymes)
- Lysozymes hydrolyse / digest pathogen
what does phagocytosis lead to the presentation of?
Phagocytosis leads to presentation of antigens where antigens are displayed on the phagocyte cell-surface
membrane, stimulating the specific immune response (cellular and humoral response)
Describe the response of T lymphocytes to a foreign antigen (the cellular response)
-T lymphocytes recognise (antigens on surface of) antigen presenting cells eg. infected cells, phagocytes
presenting antigens, transplanted cells, tumour cells etc.
- made in the thymus gland
-Specific helper T cells with complementary receptors (on cell surface) bind to antigen on
antigen-presenting cell → activated and divide by mitosis to form clones which stimulate:
● Cytotoxic T cells → kill infected cells / tumour cells (by producing perforin)
● Specific B cells (humoral response - see below)
● Phagocytes → engulf pathogens by phagocytosis
- become memory T-cells which do the above upon reinfection
describe the specific response
-leads to immunity- long term resistance
- there are 2 types:
1. cellular(in cell) response (call mediated immunity) for use on foreign cells
2. humoral response (anything that travels in the blood) for use on non-cellular foreign bodies
what are the possible targets of cells?
- foreign transplanted cells
- a virus infected cell
- cancer cells
- phagocytes that are presenting foreign antigens
diagram of the cellular response
what is the humoral response?
- carried out by the B-lymphocytes (made in the bone marrow)
- can destroy pathogens outside the cells
- leads to antibody production
- they need some help from helper T-cells
Describe the response of B lymphocytes to a foreign antigen (the humoral response)
-B lymphocytes can recognise free antigens eg. in blood or tissues, not just antigen presenting cells.
1. Specific B lymphocyte with complementary receptor (antibody on cell surface) binds to antigen via endocytosis
2. B-lymphocyte presents foreign antigen on cell membrane
3.Th will bind to presented antigen and trigger mitosis
4.This is then stimulated by helper T cells (which releases cytokines)
5. So divides (rapidly) by mitosis to form clones
6. Some differentiate into B plasma cells → secrete large amounts of (monoclonal) antibody
7. Some differentiate into B memory cells → remain in blood for secondary immune response
diagram of B- cell 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
describe the structure of antibodies
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 the 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 differences between active and passive immunity
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 / recognise changed antigen on secondary exposure
○ Specific antibodies not complementary / cannot bind to changed antigen
Describe the structure of a HIV particle
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 / incorporated into helper T cell DNA (may remain latent)
- Viral protein / capsid / enzymes are produced
- these proteins are made using host ribosomes
- 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
