Defense System

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Defense System

• Introduction
• Non-specific Defense Mechanism
• Specific Defense Mechanism
• Chemotherapy Antibiotics

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1. Introduction

• Protection against diseases by
• Non-specific defense mechanism
• Combat against any type of pathogens on their
  invasion
• Specific defense mechanism
• Depend on specific recognition of the invading
  pathogen for action

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2. Non-specific defense mechanism

• Physical barriers
• Skin (stratified squamous epithelium of
  epidermis)
• Mucous membranes of the respiratory tract
• Form a natural physical barrier
• Prevent the entry of pathogens
• The first line of defense

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• Chemical barriers

• Gastric juice in stomach -- powerful sterilizing
  liquid
• Lysozyme in tissue fluids -- lyse many bacteria

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• Phagocytosis

• Eating process
• Phagosome surrounds the pathogen
• Lysosomes fuse with the phagosome to digest and
  destroy the pathogen
• Residues discharged out of the cell

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• Inflammatory Response

• Large number of phagocytes are attracted to the
  wound area
• Engulf and kill the pathogens

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• Infected or injured cells release chemical alarm
  signals, e.g. histamine (??) causing
• Blood vessels dilate
• ? Blood flow to the area increases, making
  infected area red and warm
• Permeability of vessel wall increased
• ? Massive flow of fluids out from the blood into
  the tissues, resulting in swelling

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• Phagocytes move out from the blood into the area,
  neutrophils and monocyte (transform into
  macrophage) engulf pathogens

• Functions of blood clotting
• Prevent loss of blood
• Prevent entry of bacteria and fungi

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3. Specific Defense Mechanism

• Characteristics
• Specificity
• Memory
• Two specific mechanisms
• Humoral Immune Response (HIR)
• Cell-mediated Immune Response (CMIR)

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• Terminology
• Antibodies
• Protein produced in response to foreign
  substances
• Can destroy or neutralize antigens
• Antigens
• Substances that can elicit a specific immune
  response
• Pathogens
• Micro-organisms that can cause diseases

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• Humoral immune response (HIR)

• Antigens e.g. bacteria, pollen, animal fur, red
  blood cells etc
• Characteristics
• B cells are involved
• Recognize specific antigen and proliferate into
  plasma cells and memory cells
• Results in production of antibodies

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Memory cell
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• Antibodies

• Y-shaped
• Protein in nature
• Two top ends of the Y are specific to the
  particular antigen
• Bind to antigen
• Help to destroy or eliminate antigens by
• Lysis
• Enhance phagocytosis
• Neutralize bacterial toxins

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• Cell-mediated immune response (CMIR)

• Antigens e.g. intracellular bacteria, viruses,
  foreign substances like skin, kidney etc
• Characteristics
• T cells are involved
• Recognize specific antigen and proliferate into
  T-killer cell, T-helper cells and memory cells

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B
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• Primary response

• Elicited when an antigen entered into the body
  for the first time
• Secondary response
• Elicited when subsequent entry by the same
  antigen
• Characteristics
• Shorter lag period
• Sharper increase and a higher level of antibodies
  produced
• High antibody level stays longer

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4. Chemotherapy antibiotics

• Chemotherapy
• administration of chemical substances, natural or
  synthetic, to kill or prevent the reproduction of
  micro-organisms
• Some of these substances are produced by
  micro-organisms, which are called antibiotics
  e.g. penicillin

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• Action of antibiotics
• Inhibit cell wall formation
• Damage cell membrane
• Interfere protein synthesis
• Inhibit nucleic acid metabolism
• Drawback of prolonged use of antibiotics
• Development of resistant strain of micro-organisms

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5. Problems arising from immune response

• A. Blood transfusion

• (1) ABO blood group
• Atypical immune response
• Natural antibody is present without previous
  exposure to antigen, e.g. blood group A person
  has anti-B antibody in the plasma
• Incompatibility in blood transfusion cause
  agglutination of RBCs and blockage of the
  recipients blood vessels
• In large scale transfusion, the antibody of the
  donors blood will also attack the RBCs of the
  recipient.

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• A. Blood transfusion

• (1) Rh factor
• Rh factor is a group of antigens on RBC surface

• Rh positive person contain the antigens
  (dominant)
• Rh negative person has no such antigens
  (recessive)

• Rh- mother carries an Rh foetus, some fetal RBCs
  may cross the placenta during labour, hence
  stimulation the mother to produce Rh antibodies
• In the following pregnancies, the anti-Rh
  antibodies can cross the placenta to attack the
  foetal RBCs
• The risk increases with each Rh pregnancy as the
  mother becomes more sensitized

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B. Organ transplant

• Surface antigens present in all body cells
• Due to difference in genome, different persons
  have different kinds of antigens (except
  identical twins)
• The new transplanted organ from the donor will be
  attacked by T cells of the recipient, causing
  rejection
• So transplanted organ must be matched with the
  recipient, destruction of bone marrow and lymph
  tissue, and immunosuppressive drugs must be taken
• May be solved by introducing stem cells into the
  body which will initiate no or low level immune
  response

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C. Allergye.g. Asthma narrowing of the bronchi
and bronchioles due to swelling of the mucous
membrane and excess mucus secretion that obstuct
the air passages

• Over-reaction of immune response to certain
  substances (allergens), e.g. pollen, fur, food,
  dust, etc., that do not stimulate a response in
  non-allergic persons
• Allergen engulfed by macrophage, and fragments
  passes to T cells
• T cells stimulate B cells to proliferate and
  differentiate into plasma cells to produce
  antibodies IgE which attaches to mast cells
• allergens entered the body attahed to mast cells,
  stimulating the cells to produce histamine, which
  cause the symptoms of allergy, e.g. rash, profuse
  mucus secretion

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D. Autoimmune Disease

• The immune system fails to recognize and tolerate
  self antigens
• So T cells are activated and results in
  production of autoantibodies
• Causing inflammation and organ damage
• E.g. Rheumatoid Arthritis destruction of joints
• E.g. Lupus Erythematosus affecting joints,
  skin, kidneys, heart, lungs, blood vessels and
  brain

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References

• N. P. O. Green, G. W. Stout, D. J. Taylor. 1993.
  Biological Science. (2nd Edition). Cambridge
  University Press.
• McGraw Hill Biology http//highered.mcgraw-hill.
  com/sites/0072437316/student_view0/
• HK Bio Web