Topic 6.3 The response to infection Flashcards
What is an antigen?
- cell surface membrane that can stimulate an immune response
- usually glycoprotein or lipid/ polysacchairde
- immune system recognises ‘self’ or ‘non-self’ which enables identification of cells from other organisms of the same species, pathogens, toxins + abnormal body cells
Outline the process of inflammation
- Damaged cells release histamines, causing vasodilation
- Blood flow and permeability of vessels increases
- White blood cells and plasma into the infected tissue
Name the 2 types of WBC involved in phagocytosis
- neutrophils
- monocytes (can becomes antigen-presenting cells)
How does phagocytosis work?
- Phagocyte moves towards pathogen via chemotaxis
- Phagocyte engulfs pathogen via endocytosis to form a phagosome
- Phagosome fuses with lysosome
- Lysozymes digest pathogen
- Phagocyte absorbs the products from pathogen hydrolysis
Explain the role of antigen-presenting cells (APCs)
- macrophage displays antigen from pathogen on its surface
- enhances recognition by T helper cells, which cannot directly interface with pathogens/ antigens in body fluid
Give 2 differences between specific and non-specific immune responses?
- non-specific (inflammation + phagocytosis) is the same for all pathogens
- specific (B + T lymphocytes) are complimentary to the pathogen
- non-specific is immediate
- specific has a time lag
Name the 2 types of specific immune response
- cell mediated
- humoral
Outline the process of the cell-mediated response
- Complimentary T helper cells (lymphocytes) bind to foreign antigen on APC
- This stimulates:
- Clonal expansion of complimentary T helper cells, become memory cells or trigger humoral response
- Clonal expansion of cytotoxic cells T cells, secrete enzyme perforin to destroy infected cells
Outline the process of the humoral response
- Complimentary T helper lymphocytes bind to foreign antigen on APC
- Release cytokines that stimulate clonal expansion of complimentary B lymphocytes
- B cells differentiate into plasma cells
- Plasma cells secrete antibodies with complimentary variable region to antigen
What is an antibody/ its structure?
- proteins secreted by plasma cells
- quaternary structure: 2 ‘light chains’ held by disulfide bridges, 2 longer ‘heavy chains’
- binding sites on variable region of light chains have specific tertiary structure complimentary to an antigen
- rest of the molecule known as the constant region
How do antibodies destroy pathogens?
- formation of antigen-antibody complex results in agglutination
- activation of complement
- opsonisation, marks microbes for phagocytosis
- precipitation/neutralisation, makes toxins insoluble
What are memory cells?
- Specialised T helper/ B cells produced from primary immune response
- Remain in low levels in the blood
- Can divide very rapidly by mitosis if organism encounters the same pathogen again
What are histamines?
chemicals released by the tissues in response to an allergic reaction
What’s a phagosome?
the vesicle in which a pathogen is enclosed in a phagocyte
What are cytokines?
cell signalling molecules with several roles in the immune system, including stimulating other phagocytes to move to the infection site
What are opsonins?
chemicals which bind to pathogens and label them so they are more easily recognised by phagocytes
What is an antibody?
a glycoprotein that is produced in response to a specific antigen
What are lymphocytes?
granulocytes made in the white bone marrow of long bones, that make up the main cellular components of the immune system
Where are B cells made?
the bone marrow
Define B cells
lymphocytes made in the bone marrow which are found both in the lymph glands and free in the body once they are mature
What are immunoglobulins?
antibodies
What are B effector cells?
divide to form the plasma cell clones
What are plasma cells?
plasma cells produce antibodies to particular antigens at a rate of around 2000 antibodies per second
What are B memory cells?
B memory cells provide the immunological memory to a specific antigen, allowing the body to respond quickly if you encounter a pathogen carrying the same antigen again
What are T cells?
lymphocytes made in the bone marrow that mature and become active in the thymus gland
What are T killer cells?
lymphocytes that produce chemicals that destroy pathogens
What are T helper cells?
lymphocytes involved in the process that produces antibodies against the antigens on a particular pathogen
What are T memory cells?
very long-lived cells which make up part of the immunological memory
What is the major histocompatibility complex (MHC)?
proteins that display antigens on the cell surface membrane
What is an antigen-presenting cell (APC)?
a cell displaying an antigen/MHC complex
Define clonal selection
the selection of the cells that carry the right antibody for a specific antigen
What are plasma cell clones?
clones of identical cells that all produce the same antibody
Define agglutination
the clumping of cells caused when antibodies bind to the antigens on pathogens
Define opsonisation
the process that makes a pathogen more easily recognised, engulfed and digested by phagocytes
Define neutralisation
the action of antibodies in neutralising the effects of bacterial toxins on cells by binding to them
What is a clone?
a group of identical cells all produced from one cell
Describe how macrophages present antigens to T helper cells
-antigen on surface of macrophage binds to receptor on T helper cell
Describe how B cells are activated
- antigen binds to B cell
- antigen binds to MHC
- T helper cells bind to B cell
- cytokines released from T cells
What are the types of immunity?
- artificial active
- artificial passive
- natural active
- natural passive
Define natural active immunity
when the body provides its own antibodies to an antigen encountered naturally
Define natural passive immunity
when antibodies made by a mother are passed to the baby via the placenta or breast milk
Define artificial active immunity
when the body produces its own antibodies to an antigen acquired through vaccination
Define artificial passive immunity
when antibodies are extracted from one individual and injected into another e.g. tetanus vaccine
Define immunisation
the process of protecting people from infection by giving them passive or active artificial immunity
What is a vaccination?
the introduction of harmless forms of organisms or antigens by injection to produce artificial immunity
Define herd immunity
produced when a high proportion of a population is immune to a pathogen, usually by vaccination, lowering the risk of infection to all, including the unvaccinated, as they are less likely to encounter the pathogen
State the pros of vaccination
- children protected against diseases which could kill or disable them otherwise
- society benefits as pool of infection is reduced through herd immunity, which protects those who cannot get vaccinated due to allergies or immune system diseases
- cost of treating serious diseases or the damage they cause is minimised for a small financial expense
State the cons of vaccination
- some live, attenuated vaccines are cultured in eggs, people with allergies can’t have them
- minority of children become very ill and may die
- suggested that mass vaccination is linked to rise in childhood asthma and allergies
- some vaccines given for societal benefit
Define attenuated pathogens
viable pathogens that have been modified so that they do not cause disease but still cause an immune response that results in the production of antibodies and immunity
What are 3 non-specific responses of the immune system?`
- inflammation
- fever
- phagocytosis
How is inflammation effective?
- histamines cause blood vessels to dilate which causes local heat and redness, local heat reduces pathogen reproduction
- histamines cause capillary walls to become leaky, plasma with leucocytes + antibodies are forced out causing damage and pain and disables pathogens
In inflammation, how are histamines releases?
when tissue is damaged, mast cells and basophils release histamines
When is a fever not effective?
when body temperature rises above 40 degrees, some enzymes denature and dangerous dehydration can occur
Why is a fever an effective response?
- raised temperatures reduces the ability of pathogen reproduction
- specific immune system works better at higher temperatures, so more successful at fighting infection
How does a fever work in viral infections?
as each virus bursts out of the cell, the temperature spikes and then returns to normal
How does a fever work in bacterial infections?
temperature rises steadily and stays high until successful treatment or the body overcomes it
Why does the body temperature rise during an infection?
when a pathogen enters it causes the hypothalamus to reset which maintains the usual body temperature. =it is rest to a high temperature
Describe how a B cell is activated
- antigen binds to B cell
- antigen binds to MHC
- T helper cells bind to B cell
- cytokines released from T helper cells
Suggest how a microscope slide could be prepared to observe cell division in B cells
- sample of B cells taken from lymph node
- stain the cells using acetic orcein
- heat and add HCL
- look for the stages of mitosis
