The Immune Response
Response to Infection
• Antigens are molecules (proteins or polysaccharides) found on the surface of cells.
• When a pathogen invades the body, the antigens on its cell surface are recognised as foreign, which
activates the immune system.
• Non-specific responses help to destroy any invading pathogen.
• Specific immunity is directed at a specific pathogen.
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, The Non-Specific Immune Response
6.7 Understand the non-specific responses of the body to infection, including inflammation, lysozyme
action, interferon, and phagocytosis.
Inflammation
• The site where a pathogen enters the body (the site of infection) usually becomes red, warm, swollen
and painful:
1. Immune system cells recognise foreign antigens on the surface of a pathogen and release molecules
that trigger inflammation, e.g. histamines.
2. The molecules cause vasodilation around the site of infection, increasing blood flow to it.
3. The molecules also increase the permeability of the blood vessels.
4. The increased blood flow brings lots of immune system cells to the site of infection and the increased
permeability allows those cells to move out of the blood vessels and into the infected tissue.
5. The immune system cells can then start to destroy the pathogen.
Phagocytosis
• A phagocyte (e.g. macrophage) is a type of white
blood cell that carries out phagocytosis
(engulfment of pathogens).
• They are found in the blood and in tissues and are
the first cells to respond to a pathogen inside of
the body.
1. A phagocyte recognises the antigens on a
pathogen.
2. The cytoplasm of the phagocyte moves around the
pathogen, engulfing it.
3. The pathogen is now contained in a phagocytic
vacuole in the cytoplasm of the phagocyte.
4. A lysosome (an organelle that contains digestive
enzymes, including lysosomes) fuses with the
phagocytic vacuole.
5. The enzyme breaks down the pathogen.
6. The phagocyte then presents the pathogen’s
antigens, so its called an antigen-presenting cell.
Interferons
• When cells are infected with viruses, they produce proteins called interferons.
• Interferons prevent viruses spreading to uninfected cells:
o They prevent viral replication by inhibiting the production of viral proteins.
o They activate cells involved in the specific immune response to kill infected cells.
o They activate other mechanisms of the non-specific immune response, e.g. promoting
inflammation.
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Response to Infection
• Antigens are molecules (proteins or polysaccharides) found on the surface of cells.
• When a pathogen invades the body, the antigens on its cell surface are recognised as foreign, which
activates the immune system.
• Non-specific responses help to destroy any invading pathogen.
• Specific immunity is directed at a specific pathogen.
16
, The Non-Specific Immune Response
6.7 Understand the non-specific responses of the body to infection, including inflammation, lysozyme
action, interferon, and phagocytosis.
Inflammation
• The site where a pathogen enters the body (the site of infection) usually becomes red, warm, swollen
and painful:
1. Immune system cells recognise foreign antigens on the surface of a pathogen and release molecules
that trigger inflammation, e.g. histamines.
2. The molecules cause vasodilation around the site of infection, increasing blood flow to it.
3. The molecules also increase the permeability of the blood vessels.
4. The increased blood flow brings lots of immune system cells to the site of infection and the increased
permeability allows those cells to move out of the blood vessels and into the infected tissue.
5. The immune system cells can then start to destroy the pathogen.
Phagocytosis
• A phagocyte (e.g. macrophage) is a type of white
blood cell that carries out phagocytosis
(engulfment of pathogens).
• They are found in the blood and in tissues and are
the first cells to respond to a pathogen inside of
the body.
1. A phagocyte recognises the antigens on a
pathogen.
2. The cytoplasm of the phagocyte moves around the
pathogen, engulfing it.
3. The pathogen is now contained in a phagocytic
vacuole in the cytoplasm of the phagocyte.
4. A lysosome (an organelle that contains digestive
enzymes, including lysosomes) fuses with the
phagocytic vacuole.
5. The enzyme breaks down the pathogen.
6. The phagocyte then presents the pathogen’s
antigens, so its called an antigen-presenting cell.
Interferons
• When cells are infected with viruses, they produce proteins called interferons.
• Interferons prevent viruses spreading to uninfected cells:
o They prevent viral replication by inhibiting the production of viral proteins.
o They activate cells involved in the specific immune response to kill infected cells.
o They activate other mechanisms of the non-specific immune response, e.g. promoting
inflammation.
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