HL Human Physiology: 11.1 Antibody Production and Vaccination Flashcards
Outline how the immune system recognises body cells?
All nucleated cells of the body possess unique and distinctive surface molecules that identify it as self
These self markers are called major histocompatibility complex molecules (MHC class I) and function as identification tags The immune system will not normally react to cells bearing these genetically determined markers (self-tolerance)
Outline how the immune system recognises foreign cells?
Any substance that is recognised as foreign and is capable of triggering an immune response is called an antigen (non self)
Some glycolipids and glycoproteins on the cell surface membranes act as antigens
Explain why red blood cells can be transferred between individuals without automatically causing immune rejection
Red blood cells are not nucleated and hence do not possess the same distinctive and unique self markers as all other body cells
What do red blood cells possess which limit the capacity for transfusion?
However, red blood cells do possess basic antigenic markers which limit the capacity for transfusion (the ABO blood system)
Red blood cells may possess surface glycoproteins (A and B antigens) either independently (A or B) or in combination (AB)
Alternatively, red blood cells may possess neither surface glycoprotein (denoted as O)
Explain the ABO blood group system as a consequence of the unique feature of red blood cells
As humans produce antibodies against foreign antigens, blood transfusions are not compatible between certain blood groups
AB blood groups can receive blood from any other type (as they already possess both antigenic variants on their cells)
A blood groups cannot receive B blood or AB blood (as the B isoantigen is foreign and will stimulate antibody production)
B blood groups cannot receive A blood or AB blood (as the A isoantigen is foreign and will stimulate antibody production)
O blood groups can only receive transfusions from other O blood donor (both antigenic variants are foreign)
Define pathogen
A pathogen is an agent that causes disease – either a microorganism (bacteria, protist, fungi or parasite), virus or prion
Define disease and illness
A disease is any condition that disturbs the normal functioning of the body (i.e. the body can no longer maintain homeostasis)
An illness is a deterioration in the normal state of health of an organism (a disease may cause an illness)
What is the general nature of pathogens?
Pathogens are generally species-specific in that their capacity to cause disease (pathogenesis) is limited to a particular species
Polio, syphilis, measles and gonorrhoea are examples of diseases caused by pathogens that specifically affect human hosts
What is the meaning of zoonotic diseases?
Certain pathogens may cross the species barrier and be able to infect and cause disease in a range of hosts
Diseases from animals that can be transmitted to humans are called zoonotic diseases (or zoonoses)
Examples of zoonotic diseases include rabies (dogs), certain strains of influenza (e.g. bird flu) and the bubonic plague (rats)
Outline various ways of disease transmission
Direct contact – the transfer of pathogens via physical association or the exchange of body fluids
Contamination – ingestion of pathogens growing on, or in, edible food sources
Airborne – certain pathogens can be transferred in the air via coughing and sneezing
Vectors – intermediary organisms that transfer pathogens without developing disease symptoms themselves
Explain the immune response against a pathogen mentioning clonal formation
When the body is challenged by a foreign pathogen it will respond with both a non-specific and a specific immune reaction
Non-specific immune cells called macrophages will engulf pathogens non-selectively and break them down internally
A proportion of macrophages (dendritic cells) will present the antigenic fragments of the pathogen to specific lymphocytes
The body contains millions of different T lymphocytes and B lymphocytes that each recognise a single, specific antigen
Antigenic fragments are presented to specific helper T lymphocytes (TH cells) that, when activated, releases cytokines
The cytokines stimulate a specific B cell that produces antibodies to the antigen to divide and form clones (clonal selection)
Most of the clones will develop into short-lived plasma cells that produce large quantities of specific antibody
A small proportion of clones will differentiate into long-lived memory cells that function to provide long-term immunity
Why several types of a helper T and B lymphocytes are activated as immune response?
Pathogens typically contain multiple distinct antigenic fragments on their surface and hence a single pathogen is likely to stimulate several different T and B lymphocytes to produce a variety of specific antibodies (polyclonal activation)
Antibodies aid in the destruction of pathogens by a number of different mechanisms: Outline Agglutination
Agglutination
Antibodies act as agglutinins causing pathogens carrying antigen-antibody complexes to clump together (agglutination)
This reduces the chance that the pathogens will spread through the body or taken into cells, instead the clumps are removed by the lymphatic system and digested by phagocytes
Antibodies aid in the destruction of pathogens by a number of different mechanisms: Outline Opsonisation
Antibodies attach to bacteria making them readily identifiable to phagocytes, this is called opsonisation
Once identified, phagocytosis occurs
Antibodies aid in the destruction of pathogens by a number of different mechanisms: Outline Neutralisation
Neutralisation of viruses and bacteria
Antibodies can combine with viruses and toxins of pathogens (e.g. bacteria) to block them from entering or damaging cell
Antibodies aid in the destruction of pathogens by a number of different mechanisms: Outline Complement activation
Antibodies can trigger proteins, called complement proteins, which create holes in the cell walls of pathogens causing them to burst (cell lysis) when ions are absorbed and water moves in by osmosis
Describe the function and mechanism of memory cells
Memory cells are produced to prevent this delay in subsequent exposures and hence prevent disease symptoms developing
When a B lymphocyte is activated and divides to form plasma cells, a small proportion will differentiate into memory cells
Memory cells are long living and will survive in the body for many years, producing low levels of circulating antibodies
If a second infection with the same pathogen occurs, memory cells will react more vigorously to produce antibodies faster
As antibodies are produced faster, the pathogen cannot reproduce in sufficient amounts to cause disease symptoms
Hence, because pathogen exposure no longer causes the disease to occur, the individual is said to be immune
Define allergen and the kind of immune response that occurs
An allergen is an environmental substance that triggers an immune response despite not being intrinsically harmful
This immune response tends to be localised to the region of exposure (e.g. airways and throat) as an allergic reaction
Outline the mechanism of an allergic reaction
An allergic reaction requires a pre-sensitised immune state (i.e. prior exposure to the allergen)
When a specific B cell first encounters the allergen, it differentiates into plasma cells and makes large quantities of antibody (IgE)
The IgE antibodies attach to mast cells, effectively ‘priming’ them towards the allergen
Upon re-exposure to the allergen, the IgE-primed mast cells release large amounts of histamine which causes inflammation
What allergic symptoms are exhibited by histamine?
The release of histamine from IgE-primed mast cells causes an inflammatory response that results in allergic symptoms
Inflammation improves leukocytes mobility to infected regions by triggering vasodilation and increasing capillary permeability
Vasodilation is the widening of blood vessels to improve the circulation of blood to targeted regions
Vasodilation causes redness (as vessel expansion moves blood closer to the skin) and heat (which is transported in blood)
Capillary permeability describes the capacity for leukocytes to leave the bloodstream and migrate into the body tissue
Increased permeability leads to swelling (more fluid leaks from the blood) and pain (swelling causes compression of nerves)
Redness, heat, swelling and localised pain are all typical symptoms of an allergic response
What is the function of vaccine?
Vaccinations induce long-term immunity to specific pathogenic infections by stimulating the production of memory cells
What is the function of vaccine?
Vaccinations induce long-term immunity to specific pathogenic infections by stimulating the production of memory cells
Explain the working of a vaccine
A vaccine is a weakened or attenuated form of the pathogen that contains antigens but is incapable of triggering disease
The body responds to an injected vaccine by initiating a primary immune response, which results in memory cells being made
When exposed to the actual pathogen, the memory cells trigger a more potent secondary immune response
As a consequence of this more potent immune response, disease symptoms do not develop (individual is immune to pathogen)
The length of time a person is immune to infection following a vaccination depends on how long the memory cells survive for
Memory cells may not survive a lifetime and individuals may subsequently require a booster shot to maintain immunity
What is the benefit of vaccination in terms of population
Vaccination confers immunity to vaccinated individuals but also indirectly protects non-vaccinated individuals via herd immunity
Herd immunity is when individuals who are not immune to a pathogen are protected from exposure by the large amounts of immune individuals within the community
