2.4 - The immune system Flashcards
What do specific molecules (proteins) on the cell surface enable the immune system to identify which can stimulate an immune response?
- pathogens
- cells from other organisms of the same species e.g from transplant
- abnormal body (cancer/tumour) cells
- toxins
What are some physical barriers to infection?
- skin (tough physical barrier)
- stomach acid (kills bacteria)
- gut and skin flora (competes with pathogens)
What are some examples of non-specific immune responses?
- inflammation
- lysozyme action
- interferon
- phagocytosis
Define antigen
foreign protein that stimulates an immune response
How does antigen variability affect disease and disease prevention?
- mutation in DNA (or viral RNA if virus)
- antigens (or attachment proteins if virus) altered
so: - for bacteria etc: antibodies no longer complementary to antigen = vaccines no longer effective so increased disease spread
- for virus: attachment protein can bind to receptors of other species etc.
Describe the process of phagocytosis
- phagosome fuses with lysosome
- virus digested by lysozymes
- antigen from virus displayed on cell-surface membrane (phagocyte becomes an antigen-presenting cell)
Where are T and B cells produced and where do they mature?
both produced in bone marrow
B mature in bone marrow and T mature in thymus gland
Describe the cellular response (T-lymphocytes)
foreign antigens presented by phagocytes bind to specific receptors on cell surface of T cells, which activates them
What do helper T cells stimulate?
- cytotoxic T cells
- more helper T cells
- B cells
- phagocytes
Describe the response of B lymphocytes to a foreign antigen in the humoral response
- B cell binds to specific complementary receptor/antigen (clonal selection)
- B cell engulfs and digests antigen then becomes an antigen presenting cell which attracts T-cell
- T-cell secretes cytokines and B cell divides by mitosis and mature into plasma cells
- plasma cells produce monoclonal antibodies
- plasma cells -> memory cells
Define antibody
a protein specific to an antigen produced by B cells
How is an antigen destroyed?
formation of antigen-antibody complex which leads to agglutination and phagocytosis of bacterial cells
What response are plasma cells involved in?
primary immune response
What response are memory cells involved in?
secondary immune response
What is herd immunity?
a large proportion of a population are vaccinated against a disease which prevents the disease spreading to unvaccinated individuals
What are vaccines?
introducing small quantities of dead/inactive pathogen into the body to stimulate a primary immune response
Describe the differences between active and passive immunity
- active involves memory cells, passive doesn’t
- active involves production of antibody by plasma cells
- passive involves antibody introduced into body from outside source
- active is long term because antibody produced in response to antigen
- passive is short term as antibody is broken down
- active can take time to develop, passive is fast acting
Draw the structure of the human immunodeficiency virus (HIV)
- lipid envelope with embedded attachment proteins
- inside protein capsid is RNA and reverse transcriptase
How does HIV cause the symptoms of AIDS?
- after infection of T helper cell, T helper cell is killed
- HIV spreads so more are killed, which weakens the immune system
Why are antibiotics ineffective against viruses? What are viruses treated with instead?
- antibiotics target the cell wall so bacterial cell cannot control entry and exit of water and will burst
- viruses have a capsid coating as they are acellular (no cell wall)
- viruses are treated with antiretroviral drugs
Define monoclonal antibody
antibody produced from a single clone of a specific B-cell
What are monoclonal antibodies are used for?
- medical diagnosis
- targeting medication to specific cell types by attaching a therapeutic drug to an antibody
- pregnancy testing
Explain the ethical issues associated with the use of vaccines and monoclonal antibodies
- some thing animal testing is unethical
- risks of vaccine must be balanced with benefits
- must be tested in humans first to determine toxicity
- very expensive
- should they be compulsory
Describe the ELISA test
- 1st antibody binds to antigen
- wash to remove unbound antibody
- 2nd antibody with enzyme attached is added
- 2nd antibody binds to antigen
- substrate added and colour changes
Give two ways in which pathogens can cause disease
- bacteria release toxins
- kill tissues/cells
Describe how a virus is replicated
- attachment proteins attach to receptors on helper T cell
- RNA enters cell
- reverse transcriptase converts RNA to DNA
- DNA inserted into helper T cell
- DNA transcribed into viral mRNA
- viral mRNA translated into new viral proteins
- viral particles assembled and released
What is the process of antibodies clumping cells together so phagocytes can find them more easily?
agglutination
What is natural active immunity?
arises from exposure to an antigen/getting disease
What is natural passive immunity?
baby receives antibodies from mother through placenta
What is artificial active immunity?
acquired through vaccinations which stimulate immune system and antibodies produced
What is artificial passive immunity?
antibodies are injected into body
Secondary immune response compared to primary
antibodies produced in higher concentration and quickly
