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The immune system
Principles of immunology
Defences
ð Primary defences – prevent entry of pathogens into the body
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ð Non-specific response – take whatever type of pathogens of pathogens get in common responses
are inflammation, fever and phagocytosis
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Phagocytosis and the role of lysosomes
ð Phagocytosis - involves phagocytes engulfing and destroying bacteria and foreign material
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Detection by chemotaxis – chemical attractants from pathogen
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Ingestion, phagocyte engulfs bacterium by wrapping
pseudopodia (extension used to engulf pathogens) to
form a vesicle (phagosome)
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Lysosomes in the phagocytes move towards the
phagosome and fuses with it to form a phago-lysosome
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The hydrolytic enzymes from the lysosome digest the
bacterium
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Indigestible material is discharged
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At the site of infection, phagocytes can engulf many
bacteria
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Antigens and antibodies
ð Antigens – molecules on the surface of cells that trigger an immune response
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ð Antibodies – proteins made by B cells in response to a particular antigen, have specific site and can
act against pathogens
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Antibody structure
ð Antibodies are also called immunoglobulin
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ð A variable region on the ends of the chains
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Complementary to the antigen
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ð Coat pathogen so that it cannot invade host cells
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ð Humoral response:
ð Involves B cells
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The immune system
ð B cells produce plasma cells when exposed to antigen
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ð Small numbers of these remain as memory cells, for secondary response
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ð T cells mature in thymus glands
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ð T cells differentiate into:
ð Helper T cells – activates cytotoxic T cells and other helper T cells
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ð T cells for delayed hypersensitivity – protect against pathogens (causes transplant rejection)
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ð Cytotoxic T cells – destroys target cells on contact
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ð Acquired immunity – when the body makes its own antibodies
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Phagocytosis – a phagocyte recognises the antigens and engulfs the pathogen
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Antigen presentation – the phagocyte presents the antigen on the cell surface
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T cell activation – the antigens on phagocytes activate T cells that will activate B cells and/or attack
the pathogen
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Clonal selection – at birth, millions of different types of B cell, each able to make a particular
antibody
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B cells multiply to
form:
i
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(Primary immune response)
ii
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(Secondary immune response)

Antigenic variability in influenza
ð Some pathogens can change their antigen surface; meaning secondary immune response for the
pathogen will not work
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ð These antigens can change regularly
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Vaccines
ð Types:
ð Whole agent vaccines e
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dead pathogens or attenuated pathogens
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g
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ð Vaccines stimulate a primary immune response so that the body can produce memory cells for that
particular virus
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The immune system
ð Successful vaccinations:
ð Suitable vaccine that is economically available in sufficient doses
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ð Administration of vaccine is done at the correct time
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Monoclonal antibodies
ð Monoclonal antibodies – antibodies produced from a single group of genetically identical B cells
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ð Cancer treatments:
ð Cancer cells have antigens called tumour markers
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ð You can attach cancer drugs to monoclonal antibodies
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ð Cancer drug will accumulate near cancer cells
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