Defense System
1. Introduction2. Non-specific Defense
Mechanism3. Specific Defense Mechanism4. Chemotherapy & Antibiotics
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
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
Chemical barriers Gastric juice in stomach -- powerful
sterilizing liquid Lysozyme in tissue fluids -- lyse many
bacteria
Phagocytosis ‘ Eating process’ Phagosome
surrounds the pathogen
Lysosomes fuse with the phagosome to digest and destroy the pathogen
Residues discharged out of the cell
Inflammatory Response
Large number of phagocytes are attracted to the wound area
Engulf and kill the pathogens
Infected or injured cells release chemical alarm signals, e.g. histamine ( 組胺 ) 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
Phagocytes move out from the blood into the area, neutrophils and monocyte (transform into macrophage) engulf pathogens
Functions of blood clottingPrevent loss of blood
Prevent entry of bacteria and fungi
3. Specific Defense Mechanism
Characteristics Specificity Memory
Two specific mechanisms Humoral Immune Response (HIR) Cell-mediated Immune Response
(CMIR)
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
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
B
B
Antigen e.g. bacteria, pollen, animal fur, red blood cells, etc
B cell
Antibody forming cell
Plasma cell
Antibodies combat against antigen
Memory cell
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
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
Antigen (e.g. bacteria, viruses, foreign substances...)
T
T
T
TT cell
Memory cell
T-killer cell /
Cytotoxic T cell
Kill antigen directly
Cytokines
B cell
Plasma cell
T-helper cell
B
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
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
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
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 recipient’s blood vessels
In large scale transfusion, the antibody of the donor’s blood will also attack the RBCs of the recipient.
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
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
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
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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