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

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/

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