06. Responding to antigens Flashcards
Describe how intact skin works to prevent disease.
A physical barrier. This means that it prevents entry of pathogens into the body.
Define pathogen
Disease causing agent
Define disease
A physical or mental disturbance involving symptoms, dysfunction or tissue damage.
Define antigen
An antigen is a unique molecule or part of a molecule that can initiate an immune response.
Give 3 reasons a pathogen is described as non-cellular
They require a host cell as they cannot reproduce outside a host cell
No metabolic cellular processes (whilst they have DNA or RNA they have no organelles to generate energy or proteins)
Not made of cells
Give 3 reasons a pathogen is described as cellular
They do not require a host cell as they can reproduce outside a host cell
Can undertake metabolic cellular processes (they have DNA or RNA and they have the organelles to generate energy or proteins)
Made of cells
Give 2 examples of non-cellular pathogens
Virus and prion
Define prion
Abnormal infectious protein
Give 4 examples of cellular pathogens
Bacteria
Fungi
Protozoa - e.g. Plasmodium (malaria)
Parasite
State the three types of barriers
Physical barriers
Chemical barriers
Microbiological barriers
Give two examples of physical barriers in a human.
Intact skin
Hairs
Give two examples of chemical barriers in a human.
Stomach acid, lysozymes
Define microbiota barrier
Themicroorganismsin a particular location (e.g. on the skin, in the gut, in the vagina) that live in a symbiotic relationship with animals to outcompete pathogens.
Give two examples of physical barriers in a plant
Intact bark
Thick waxy cuticle
Thorns or trichomes (hair like structures)
Position of stomata
Formation of galls
State a chemical barrier in a plant
They can secrete many antimicrobial proteins OR secrete odour chemicals such as peppermint/caffeine.
Describe the Rhizosphere in a plant
Rhizosphere is a microbiota barrier in a plant. This means that it is inhabited by a unique population of microorganisms to outcompete the pathogenic bacteria in the soil by synthesising and releasing toxins.
Describe how hydrochloric acid works to prevent disease.
Chemical barrier. This means that it destroys pathogens that enter the stomach.
Name the main components of the lymphatic system
Bones
Lymph vessels
Lymph fluid
Lymph nodes
Describe the lymph
A colourless fluid containing white blood cells. This means that it bathes the tissues and drains through the lymphatic system into the bloodstream.
Compare the circulatory system (the cardiovascular system) with the lymphatic system
Circulatory has a pump whereas lymph has no pump
Circulatory contains red blood cells (RBC) whereas lymph has no RBC
Circulatory system has (some vessels) with no valves where as all of the lymphatic vessels have valves
Circulatory system fluid is called plasma where as lymphatic system the fluid is called lymph
Give the function of the bone marrow
Site where white blood cells (macrophage, neutrophil, dendritic, T and B lymphocytes) are made and mature.
Give the function of the lymph node
Site of antigen recognition. This means that it is where antigen presenting cells meet T and B cells for clonal selection, differentiation and expansion of the T and B cells in the adaptive immune response.
Describe the two functions of phagocytes
Phagocytosis. This means that they recognise, engulf and digest foreign material, such as pathogens.
Antigen presenting cells (macrophage or dendritic). This means that they will move from the site of infection to the lymph node to present non-self antigens on MHCII to T and B cells to initiate the adaptive immune response.
Sate what line of defence phagocytosis is a part of
Second/innate/non-specific
State what types of cells have an MHCI marker
All cells with a nucleus (so RBC don’t)
Describe the steps of phagocytosis
- Phagocyte recognises a non-self antigen and engulfs pathogen forming a phagosome
- Phagosome fuses with lysosome forming a phagolysosome
- Pathogen destroyed by digestive enzymes in lysosome
- Destroyed pathogen removed from the cell by exocytosis
Give three types of phagocyte
Neutrophil, macrophage and dendritic cell
Describe the function of an eosinophil
Eosinophils are large granulated cells containing various enzymes that recognize and destroy invading pathogens which are too large to be broken down by phagocytosis. This means that mediators such as DNases, RNases, and proteases, help destroy invading pathogens.
Give the function of a natural killer cell
Recognise non-self antigens on MHCI markers and release cytotoxic chemicals which destroy the virally infected or cancer cell.
Give the functions of complement proteins
Chemotaxis – complement proteins gather near a pathogen and attract phagocytes to it making phagocytosis easier/
Opsonisation - attach to non-self-antigen on B cells making them easier to identify and making phagocytosis easier. [1]
Lyse B cell plasma membranes by forming a membrane attack complexes [2]
Promote inflammation by recruiting inflammatory cells which destroy the B cell.
Describe the function of interferons
Interferons are secreted by cells when they are infected with a virus. This means that the interferons interact with receptors on neighbouring cells, causing them to undergo a number of changes that make them less susceptible to viral infection. This helps prevent the virus from spreading between cells.
State the two steps which B cells need to activate in the lymph node
An antigen presenting cell needs to present a specific and complementary non-self antigen on an MHCII marker and this needs to bind to the antigen binding site of the antibody
Recieve a cytokine signal from a T helper cell
State the two steps which T cytotoxic cells need to activate in the lymph node
An antigen presenting cell needs to present a specific and complementary non-self antigen on an MHCII marker and this needs to bind to the T cell receptor
Recieve a cytokine signal from a T helper cell
Outline the steps of the humoral immune response in the lymph node
Clonal selection occurs. This means that the antigen presenting cell that has moved from the site of infection to the lymph node to present a non-self antigen on an MHCII marker to a B cell and T helper cell which causes the T helper cell to release cytokines to activate the naive B cell.
Clonal differentiation and expansion occurs. This means that the B cell divides by mitosis forming a B memory cell and a plasma cell. The plasma cell then secretes specific, complementary and free floating antibodies.
The B memory cell remains in circulation to provide long term immunity.
Outline the functions of antibodies
All antibodies have a specific and complementary antigen binding site to an________ antigen so…
Agglutination of ____ pathogens occurs. This means that there are less pathogens circulating and makes phagocytosis of more pathogens easier.
Neutralisation of ____ toxins/ ____ virus occurs. This means that they become inactive and will reduce the severity of disease.
Opsonisation occurs by attaching to ____pathogens. This means that phagocytosis is more likely as they have been marked for destruction.
Activate complement proteins. This means that phagocytosis ismore likely as they have been marked for destruction.
Describe what provides long term immunity in the humoral immune response.
B memory cells remain in circulation. This means that on secondary infection with the same pathogen they can divide more rapidly and lead to more B memory cells and more plasma cells which secrete a higher concentration of specific complementary and free floating antibodies more rapidly.
Compare natural killer cells with T cytotoxic cells
Natural killer (NK) cells are non-specific whereas T cytotoxic (T cyto.) are specific
NK have no memory cells whereas T cyto. have memory cells
Both look for non-self antigens presented on MHCI markers.
Both release perforins/cytotoxic chemicals/death ligands to initate destroying virally infected cells or cancer cells.
Outline the steps of inflammation.
Damaged cells/tissues release cytokines. These attract neutrophils to the site of infection and activate mast cells to release histamine.
Histamine causes vasodilation which is more blood flow to the area. This means that there will be more macrophages, neutrophils and dendritic cells brought to the site of infection and cause redness and an increase in temperature.
Histamine also causes an increase in membrane permeability. This means that more tissue fluid leaks out causing swelling and pain and means that the phagocytes can reach the tissues and help eliminate the pathogen by phagocytosis.
State how antibodies attach to a non-self antigen/toxin/allergen
By their specific and complementary antigen binding site
Outline the steps in the cell-mediated immune response
Clonal selection occurs. This means that the antigen presenting cell /macrophage/dendritic cell moves from the site of infection to the lymph node [1]
to present a non-self-antigen from coronavirus on an MHCII marker to a T cytotoxic cell and T helper cell [1]
which causes the T helper cell to release cytokines to activate the T cytotoxic cell. [1]
Clonal differentiation and expansion occurs. This means that the T cytotoxic cell divides by mitosis forming an active T cytotoxic cell and a T cytotoxic memory cell. [1]
The active T cytotoxic cell then releases cytotoxic chemicals to kill virally infected cells (once it recognises the non-self covid antigen on MHCI markers. [1]
