6. Responding to Antigens Flashcards
Define an antigen.
An antigen is a unique molecule or part of a molecule that can initiate an immune response.
Define a pathogen.
A pathogen is a disease-causing agent
How is non-cellular defined?
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
How is cellular defined?
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
How is intracellular defined?
Grow and reproduce inside of a host cell
How is extracellular defined?
Grow and reproduce outside of a host cell
What are prions?
Prions are abnormal infectious proteins.
Are prions cellular or non-cellular? Intracellular or extracellular?
Non-cellular, intracellular
Are viruses cellular or non-cellular? Intracellular or extracellular?
Non-cellular, intracellular
What is a virus composed of?
Genetic material (DNA or RNA) and protein coat (capsid)
Are bacteria cellular or non-cellular? Intracellular or extracellular?
Cellular, both intracellular and extracellular
Are fungi cellular or non-cellular? Intracellular or extracellular?
Cellular, extracellular
Are protozoa cellular or non-cellular? Intracellular or extracellular?
Cellular, extracellular
How do bacteria cause disease?
Release toxins and rapidly reproduce via binary fission (causing an increase in toxin concentration)
What is the difference between an endoparasite and an exoparasite?
Endoparasites live inside a host whereas exoparasites live on the outside of a host
Are parasites cellular or non-cellular? Intracellular or extracellular?
Cellular (multicellular), extracellular
What are the three types of barriers?
Physical, chemical, microbiota
What is the first line of defence?
Barriers
What is a physical barrier?
physical structures that prevent the pathogen from entering
What are examples of physical barriers and how do they prevent the entry of a pathogen in humans?
Intact skin prevents the entry of pathogens
Hairs in our ears and nose trap foreign particles
Ear wax traps foreign particles
What is a chemical barrier?
some type of secreted chemical that helps prevent the entry of a pathogen
What are examples of chemical barriers and how do they prevent the entry of a pathogen in humans?
Sweat secretes both salt and fatty acids which are bacterial inhibitors and prevent pathogen infection.
Saliva and tears secrete lysozymes which are enzymes that break bacterial cell walls, so bacterial cells burst due to osmosis.
The lungs secrete a mucus from goblet cells that helps trap dirt and pathogenic particles, this mucus is then removed via the cilia that pass the mucus up and out of the lungs and nose.
The stomach secretes a strong hydrochloric acid which kills the majority of pathogens that enter via the digestive system.
What is an example of a microbiota barrier in humans?
Many microbes live in a symbiotic relationship with humans these microbes outcompete pathogenic bacteria preventing them establishing colonies in the human body e.g. on the skin or in the alimentary canal.
What are examples of physical barriers and how do they prevent the entry of a pathogen in plants?
Intact bark and thick waxy cuticles provide a protective coat through which pathogens cannot enter.
Hair on the leaves and surrounding the stomata prevent the entry of pathogens.
Galls are abnormal swellings at the infection site which limit the movement of the pathogen by trapping it in this area.
Stomata are often sunken within the leaf to prevent pathogens entering.
What are examples of chemical barriers and how do they prevent the entry of a pathogen in plants?
Secretion of enzymes
Secretion of toxins e.g. Phytoalexins which are antimicrobial compounds produced by damaged plant cells
Odour chemicals e.g. peppermint that act as natural pesticides
Coffee plants use caffeine to ward off insects
When a plant is wounded resin is secreted which closes the wound over to prevent pathogen entry.
What is an example of a microbiota barrier in plants?
Rhizosphere is the area around a plant root that is inhabited by a unique population of microorganisms and is influenced by the chemicals released from plant roots, this acts as a microbiota barrier in plants as the naturally occurring bacteria outcompete the pathogenic bacteria in the soil
What are the roles of the lymphatics sytem in the immune response?
Transport system for phagocytes/T and B cells/natural killer cells/eosinophils
Site of antigen recognition by T and B cells (in lymph node).
What are examples of lymphocytes?
T cells, B cells, Natural Killer cells
What is the role of the thymus?
Maturation of T lymphocytes
What is the function of the bone marrow?
Produce white blood cells and maturation of B lymphocytes
What is the purpose of valves in the lymphatic system?
Keep lymph flowing in one direction (unidirectional)
What is the relationship between plasma, tissue fluid and lymph?
Plasma is the fluid component of blood in the circulatory system, when this leaks out of capillaries it is referred to as tissue fluid, 90% of this tissue fluid is reabsorbed by the capillaries and 10% enters the lymph vessel where it is now known as lymph. Lymph fluid returns back to the blood via the lymphatic system.
What are the characteristics of innate immunity?
Acts broadly against actions of pathogens
Reaction is same for ALL pathogen
Has no ‘memory’ of previous pathogen
Response level is the same for all non-self material encountered
Response is immediate
What is the role of a phagocyte?
Recognise, engulf and digest foreign material, such as pathogens, through phagocytosis.
Give 3 examples of phagocytes.
Neutrophil, macrophage, dendritic cell
List the cells of the innate immune response.
Phagocytes (neutrophils, macrophages, dendritic cells), mast cells, eosinophils, natural killer cells
Describe two roles of a phagocyte
Antigen presenting cell (macrophage and dendritic) this means that it moves from the site of infection to the lymph node to present the non-self antigen of the engulfed pathogen on its MHCII marker to initiate the adaptive immune response.
Phagocytosis this means that it will recognise, engulf and digest foreign material, such as pathogens
What is the role of a complement protein?
Chemotaxis. This means that the complement proteins gather near the (context) pathogen and attract phagocytes to it making phagocytosis easier.(1)
Opsonisation. This means that they attach to non-self antigen on (context) pathogen making them easier to identify and making phagocytosis easier.(1)
Lyse plasma membrane of (context) bacteria pathogen so it will die.(1)
Promote inflammation. This means that it will will help eliminate (context) pathogen.(1)
What is the role of a cytokine?
These proteins act as messengers between cells of the immune system, as well as other body systems e.g. nervous system
What is the role of interferon?
Secreted by cells when they are virus infected, this warns other nearby cells and makes them more virus resistant
What is the role of eosinophils?
They will target extracellular pathogens that are too large to be engulfed by the phagocytes eg. parasites
What is the role of a natural killer cell?
They recognise non-self antigen on MHCI markers and release cytotoxic chemicals which destroy the virally infected cell or cancerous/tomour cell
Which cells have MHCI markers?
All nucleated cells of the body
Which cells have MHCII markers?
Macrophage and dendritic
Describe what occurs to cause swelling in the inflammation process
An increase in permeability of blood vessels occurs, this means that more plasma leaks into the tissue, increasing tissue fluid and causing swelling (and also trapping the pathogen in the area)
Describe what occurs to cause redness in the inflammation process
Vasodilation occurs this means that more blood goes to the site of infection causing it to become red
Describe what occurs to cause heat in the inflammation process
Vasodilation occurs this means that more blood goes to the site of infection causing it to heat up
Describe what occurs to cause pain in the inflammation process
An increase in permeability of blood vessels occurs, this means that more plasma leaks into the tissue, increasing tissue fluid and causing it to press on nerve endings
What pathogens does the humoral response target? Which cells are involved?
Extracellular pathogens, B lymphocytes
How do antibodies work?
Immobilising pathogens- sticking to non-self antigens of pathogen prevent these binding to a receptor
Agglutination of pathogens - clumping together
Flagging of pathogens for phagocytosis
Activate complement proteins
What is clonal selection? And name the location where it occurs.
The specific and complementary T helper cell is selected when an antigen presenting cell presents a non-self antigen to it. This T helper cell secretes cytokines to active a B cell. This B cell is then selected as it recieves this cytokine and it’s membrane bound antibodies bind to the non-self antigen presented by an antigen presenting cell.
This occurs in the lymph node
What is clonal differentiation?
B lymphocytes divide to become either Plasma cells or B memory cells
What is clonal expansion?
When the B cell has attached to the antigen it then rapidly divides by mitosis forming plasma cells and B memory cells
What is the function of a plasma cell?
Plasma cells produce specific and complementary free-floating antibodies
What is the function of a B memory cell?
Remain in circulation after the pathogen has been dealt with and when the same pathogen is encountered again, they divide by mitosis more rapidly forming Plasma cells and more B memory cells. This leads to a higher concentration of anitbodies.
How does the secondary immune response differ from the primary immune response?
The secondary immune response has a more RAPID production in the secondary response, and a HIGHER CONCENTRATION of antibodies
What is the function of a cytotoxic T cell?
Recognise non-self antigens on MHCI markers of infected body cell (particularly with a virus), tumour cells or foreign tissues and produce cytotoxic chemicals (perforins) that destroy the target cell by causing holes in the plasma membrane.
Compare a cytotoxic T cell and a natural killer cell.
A cytotoxic T cell is a part of the adaptive immune response whereas a natural killer cell is a part of the innate immune response.
A cytotoxic T cell forms T memory cells/immunological memory whereas a natural killer cell does not.
Define disease
Physical or mental disturbance involving symptoms, dysfunction or tissue damage
Describe inflammation
Damaged cells/tissues release cytokines.
Mast cells are activated. This means that they release histamine.
Histamine causes an increase membrane permeability. This means that more tissue fluid leaks out causing swelling and pain.
Histamine also causes vasodilation. This means that there is more blood flow to the area to bring more immune cells and cause redness and an increase in temperature.
