Immune system

1
Immune system

• By the end of the lesson you should be able to
• Outline the stages in phagocytosis.
• Describe how antibodies work and how they are
  specific.

2
First lines of defence
tears antibacterial
enzymes
saliva antibacterial enzymes
mucus linings traps dirt and microbes

• skin prevents entry

stomach acid low pH kills harmful
microbes
good gut bacteria out compete bad
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Pathogens

• disease causing micro-organisms
• bacteria
• virus
• fungi,
• protozoa,
• parasite,
• prion

4
Second lines of defence

• Involves white blood cells
• Non-specific response
• invading pathogens are targeted by macrophages
• Specific response
• lymphocytes produce chemicals called antibodies
  that target specific pathogens

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Phagocytes
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Phagocytes

• Monocytes and macrophages
• Provide a non-specific response to infection
• http//www.microbelibrary.org/images/tterry/anim/p
  hago053.html

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Phagocytosis

• Stages in phagocytosis
• Phagocyte detects chemicals released by a foreign
  intruder (e.g. bacteria)
• Phagocyte moves up the concentration gradient
  towards the intruder
• The phagocyte adheres to the foreign cell and
  engulfs it in a vacuole by an infolding of the
  cell membrane.
• Lysosomes (organelles which are rich in digestive
  enzymes found in the phagocytes cytoplasm) fuse
  with the vacuole release their contents into it.

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Phagocytosis

• The bacterium is digested by the enzymes, and the
  breakdown products are absorbed by the phagocyte.
• During infection, hundreds of phagocytes are
  needed.
• Pus is dead bacteria and phagocytes!
• link to phagocytosis

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Pus

• An accumulation of -
• dead phagocytes
• destroyed bacteria
• dead cells

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Lymphocyte
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Lymphocytes

• Provide a specific immune response to
• infectious diseases.
• There are 2 types -
• - T-cells - B-cells
• They produce antibodies.

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Antigens

• all cells have surface markers called antigens.
• body can recognise these as self or non-self
  (foreign)

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Specific response

• Lymphocytes detect presence of foreign antigens
• Stimulated to produce
• specific proteins called
• antibodies.

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• antibodies combine with their specific antigen
  (like a lock and key)
• this renders the pathogen harmless.
• primary response

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Immunity

• the bodies ability to resist infection
• can be natural or acquired

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Immunological memory

• after an infection is fought off some lymphocytes
  become memory cells.
• if same pathogen returns memory cells stimulate
  the produce the specific antibody very rapidly.
• the infection is fought off before symptoms
  appear secondary response
• vaccines can stimulate same response

17
Immune system

• Can you
• Outline the stages in phagocytosis.
• Describe how antibodies work and how they are
  specific.

18
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