A7 Immunity Flashcards
Name the type of white blood cell shown in the picture.
(It has been stained purple)
Phagocyte
Name the type of white blood cell shown in the picture.
(It has been stained purple)
Lymphocyte
What is an antigen?
Cell surface molecule which can stimulate an immune response.
Usually a glycoprotein or sometimes glycolipid or polysaccharide
Describe the process of phagocytosis
- Phagocyte moves towards pathogen via chemotaxis
- Phagocyte engulfs pathogen to form phagosome.
- Phagosome fuses with lysosome to form a phagolysosome
- Lysozymes/enzymes digest pathogen
- Phagocyte absorbs products from pathogen hydrolysis
Explain the role of antigen presenting cells in producing an immune response
Phagocyte displays antigen from pathogen on cell membrane
TH cells bind to antigen and are activated
Binds to specific B and T cells and causes clonal selection/mitosis
Name the 2 types of specific immune response
Humoral
Cell mediated
Outline the process of cell mediated response
- Complementary TH lymphocytes bind to foreign antigen on antigen presenting cell
Release cytokines that stimulate
(a) Clonal expansion of complementary TH cells (rapid mitosis) become memory cells or trigger humoral response
(b) Clonal expansion of cytotoxic T cells which secrete enzyme perforin which creates holes in the target cell membrane and destroys the infected cells.
Outline the process of the humoral response
- Complementary TH lymphocytes bind to foreign antigen on antigen presenting T cells.
- Release cytokines that stimulate clonal expansion (rapid mitosis) of complementary B lymphocytes
- B cells differentiate into plasma cells
- Plasma cells secrete antibodies with complementary variable region to antigen
- Cause agglutination and efficient phagocytosis
What is an antibody?
Proteins secreted by plasma cells
Quaternary structure - 2 light chains held together by disulfide bridges to 2 longer heavy chains.
Binding sites on variable region of light chains have specific tertiary structure complementary to antigen
Rest of molecule know as constant region
Name the type of specialised cell that can make the molecule shown in the diagram
Plasma cell
How do antibodies lead to the destruction of a pathogen?
Formation of antigen-antibody complex results in agglutination which enhances phagocytosis
What are monoclonal antibodies?
Antibodies produced from a single clone of B cells.
What are memory cells?
Specialised B and T cells produced from primary immune response
Remain in low levels in the blood
Can divide rapidly by mitosis if organism encounters the same pathogen again.
Contrast the primary and secondary immune response
Secondary response
Faster rate of antibody production
Shorter time lag between exposure and antibody production
Higher concentration of antibodies
Antibody level remains higher after the secondary response
Pathogen usually destroyed before any symptoms
What causes antigen variability?
Random genetic mutation changes base sequence
Different sequence of codons on mRNA
Different primary structure of antigen as H bonds, ionic and disulfide bridges form in different places in tertiary structure
Different shape of antigen
Explain how antigen variability affects the incidence of disease
Memory cells no longer complementary to antigen, individual not immune, can catch disease again
Many varieties of a pathogen - difficult to develop a vaccine containing all antigen types
Compare passive and active immunity. Give examples of both types
Both involve antibodies
Both can be artificial or natural
Passive natural - antibodies in breast milk/across placenta
Passive artificial - anti-venom, needle stick injections
Active natural - humoral response to infection
Active artificial - vaccination
Explain the principles of vaccination
Vaccine contains dead/inactive form of a pathogen/antigen
Triggers primary immune response
Memory cells are produced and remain in the blood so secondary response is rapid and produces higher concentration of antibodies
Pathogen is destroyed before it causes symptoms
What is herd immunity?
Vaccinating large proportion of population reduces available carriers of the pathogen
Protects individuals who have not been vaccinated
Suggest some ethical issues surrounding the use of vaccines
Production may involve use of animals
Potential dangerous side effects
Clinical tests may be fatal
Is it acceptable to trail new vaccines in developing countries
Can individuals be forced to get vaccinated int he interest of public health?
Should expensive vaccines be developed for rare diseases
Describe the structure of HIV
Genetic material (2xRNA) & viral reverse transcriptase
surrounded by capsid
Surrounded by viral envelope derived from host cell membrane
(GP120) attachment proteins on surface
How does HIV result in the symptoms of AIDS?
Attachment proteins bind to complementary (CD4) receptor on TH cells.
HIV particles replicate inside Tcells killed or damaging the,
AIDS develops when there are too few T cells for the immune system to function
Individuals cannot destroy other pathogens & suffer from secondary diseases/infections
Why are antibiotics ineffective against viruses?
Antibiotics interfere with the production of murein/peptidoglycan cell wall - viruses have no cell wall
Antibiotics interfere with protein synthesis- viruses use host cell organelles to make proteins.
Viruses replicate indie host cells - difficult to destroy them without damaging normal body cells.
Suggest 2 clinical uses of monoclonal antibodies
Pregnancy tests by detecting HCG hormones in urine
Diagnostic procedures eg ELISA test
Targeted treatment by attaching drug to antibody which delivers drug to cells with abnormal antigen
Explain the principle of a direct ELISA test
Detects presence of a specific antigen
Monoclonal antibodies bind to bottom of test plate
Antigen molecules in sample bind to antibody
Mobile antibody with reporter enzyme attached binds to antigen that are fixed on the monoclonal antibodies. Rinse.
Add substrate for reporter enzyme, Positive result causes a colour change.
Explain the principle of an indirect ELISA test
Detect presence of an antibody against a specific antigen
Antigens bind to bottom of test plate
Antibodies in sample bind to antigen
Wash away excess
Secondary antibody with reporter enzyme attached binds to primary antibodies from the sample
add substrate for reporter enzyme. Positive result - colour change
What is immunity?
When a body’s defences are able to kill a pathogen before it causes harm
Identify 2 types of white blood cell
Phagocytes
B lymphocytes
T lymphocytes (TH and TC cells)
How is the immune response controlled in organ transplant patients to prevent organ rejection?
Immunosuppressant drugs
Close tissue match
Why is there a time lag between infection and an immune response?
Phagocytosis and production of antigen presenting cell
Clonal selection takes time ie correct lymphocyte binding to the non self antigen
Name 4 antigen presenting cells
Pathogens
Antigen presenting phagocytes
Transplanted organs
Toxins from pathogen
Cancer cells
List the non-specific defences against infection
Skin, Tears, Earwax, Mucus, Stomach acid
Phagocytosis
What is a pathogen?
A microorganism that causes infectious disease
Which type of immunity are T lymphocytes mainly involved in?
Cell mediated
Can T lymphocytes bind to non-self antigens in the blood?
No they can only bond to foreign antigens presented on a cell membrane
What can cloned T lymphocytes do after clonal expansion has taken place in the cell mediated response?
Become memory cells for rapid future response to same pathogen
Stimulate phagocytes to engulf pathogens
Stimulate B cells to divide and release antibodies
Activate cytotoxic T cells
B lymphocytes can develop into which types of cells during an immune response?
Plasma cells
Memory cells
What is the function of a plasma cell?
Produce antibodies which destroy pathogens
Name the type of molecule shown in the diagram
Antibody
Describe how the presentation of a viral antigen leads to the secretion of antibodies against the viral antigens.
T cells bind to antigen on phagocyte
T cells are activated to form T helper cells
T helper cells stimulate SPECIFIC B cells
B cells stimulated to divide by mitosis
Form plasma cells which release antibodies
How many polypeptides make up an antibody?
4
What does the antibody binding site bind to?
Complementary antigen
What is formed when and antibody binds to an antigen?
Antigen-antibody complex
Describe how monoclonal antibodies can be used to treat cancer?
Produce monoclonal antibodies specific to the antigen on the cancer cell
Inject into patient
Antibodies block chemical signals that stimulate uncontrolled ell division
Why are monoclonal antibodies a better treatment in some cases than drugs?
Fewer side effects due to treatment being directed to target cells
Radioactive or cytotoxic drugs can be attached to monoclonal antibodies.
How do these kill caner cells?
Antibody with attached drug binds to antigens on cancer cell.
Drug kills the cell
What are the ethical issues related to the use of monoclonal antibodies?
Mice used to produce tumour cells and spleen used to obtain monoclonal antibodies
Some deaths associated with their use (in treatment of MS). Patients must give informed full consent
Accidents in medical trials involving human volunteers
Give the differences between passive and active immunity.
Active involves memory cells (passive does not)
Active produced antibodies from plasma cells
Active provides long term immunity (passive short term)
Active slower acting
What are the features of a successful vaccination programme?
Economically viable to make on large scale
Few side effects
Easy to produce, store and transport
Easily administered
Vaccinate a large proportion of the population
Why does vaccination rarely eradicate disease?
Immunity not induced by those with weakened immune system
Possible to catch disease until immunity is achieved
Pathogens may mutate so antigens change
many strains of a particular pathogen
People refuse to get themselves or children vaccinated.
