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Immune
system
Functions of immune system
 Protect against
infection by microbes.
 Isolate or remove
nonmicrobial foreign
substances.
 Destroy cancer cells
that arise in the body.
Body Defense System
Non- specific
Passive
Active
~Mechanical ~ Phagocytosis
barrier
~Chemical
barrier
~Blood clots
~ Inflammation
Specific
Humoral
Cell-mediated
Immune
Immune
Response
Response
(HIR)
(CMIR)
Body Defense System
 Non-specific
mechanism
 Specific mechanism
Non- specific mechanism
 Non-specific mechanism
~ do not depend on previous exposure
~ do not selectively protect against foreign
substance
a) Passive mechanism
b) Active mechanism
Passive mechanism
Mechanical skin & epithelium, ciliated
epithelium & mucus
Chemical barrier  acid in gastric juice,
tears, sebaceous secretion, nasal
secretions & saliva, acidic secretion in
vagina
Blood clots  blood clots prevent further
blood loss & entry of pathogenic microorganisms
Active mechanism
Phagocytosis
~ invading microorganisms are
engulfed by
phagocytes
Phagocytosis I
Chemicals released by
bacterium are detected by
neutrophil
Plasma proteins become attached to
bacterium aid identification by
neutrophil & adherence of bacterium
to neutrophil
Neutrophil moves
towards bacterium
Phagocytosis II
Phagosome formed by pseudopodia
Phagocytosis III
Lysosome fuses with
phagosome and releases
hydrolytic enzymes
Digestion of bacterial call and
absorption of products into
neutrophil
Phagocytes
 amoeboid cells attracted to damaged
area
 stimulus for migration  chemical liberated by
the ruptured blood cells & tissues
 found in liver, spleen & lymph nodes
 engulf toxic foreign particles localize infection
Inflammation
The body’s response to injury. It involves
pain, heat, redness, swelling and loss of
function of the affected part.
Active mechanism - Inflammation
Bacteria invade the
body

vasodilatation of
affected
region

 blood supply
reddening, swelling,
 temp. , pain
Biological significance of
inflammation
 enables neutrophils migrate to the
destroyed area & engulf invaders.
 localizes the invading pathogens
 plasma protein i.e. fibrinogen blood clot
 excess tissue fluid dilute & negate
potential toxic irritants
Specific defense mechanism
 It depends upon, prior exposure to the specific
foreign substances, recognition of it upon
subsequent exposure, and the reaction to it.
Terminologies
 Antigen ~ foreign body to the host
 Antibody ~ blood protein in response to
its corresponding antigen;
~circulates in blood to attack
antigen & render it’s
harmless.
Specific defense mechanism
 Toxoid ~ non- toxic protein toxin, useful
in vaccines
 Endotoxin ~ toxic substance produced by
bacteria, stay in cell wall
 Antitoxin ~ antibody counteracting toxin
produced by specific antigen
 Lymphocytes ~ a variety of white blood
cells
Types of lymphocytes
 T- lymphocytes (T- cells)
~ circulate permanently in
the blood once produced,
~ colonize in lymph nodes
~ for cell- mediated
immune response
~ do not synthesize
antibody
Lymphocytes
 B- lymphocytes (B-cells)
~ circulate between blood
stream & lymphoid
organs
~ less than T- cells
~ for humoral immune
response
~ able to synthesize
antibodies
T & B cells
B cells
 for humoral immune
response (HIR)
 thymus independent
 with finger- like
projection on surface
 synthesize antibodies
when stimulated by
antigens
T cells
 for cell- mediated
immune response
(CMIR)
 thymus dependent
 smooth cell surface
 do not synthesize
antibody
Humoral immune response (HIR)
 by B cells
 also called antibody- mediated immunity
Clonal selection  B cell proliferation
plasma cells & B memory  differentiation
cells
Humoral Immune
Response (HIR)
Antibody
 Protein in nature
 Synthesized by
plasma cells once
stimulated by antigen
 Ig :2 identical heavy
chains (H chain ) +
2 identical light chain
(L chain)
 A family of proteins
with variation in
antigen- binding
capacities
Humoral immune response
B cells for self proteins will be destroyed
during fetal life.
Antigen do not provide information to
plasma cells but select those which can
tailor make the specific antibodies.
The unique DNA base sequence in
lymphocytes determine the specificity of
antibody.
Action of antibodies
 Lysis of cell membrane
 Agglutination
 Stimulation of phagocytosis
 Neutralization of toxins
Secondary response of HIR
Memory cells  activate body response to
second infection of the antigen
Enables prompt & vigorous response in
second encounter
 short latent period
 higher production of antibodies
 high specificity
 larger population of memory cells
Cell- mediated immune response (CMIR)
 by T cells
 do not possess antibodies
 thymosin promotes T cell maturation
CMIR
HIR vs CMIR
 HIR
Time course
Primary response: 4-5
days
Secondary response: 12 days
Venue
B cell : lymphoid tissues
e.g. lymph nodes, liver
 CMIR
Time course
1 - 2 days
Venue
T cell: circulating
around
Importance of HIR
Antibodies ~ act against bacteria,
viruses & toxic matters.
Memory cells~ prevent disease.
Immunoglobulins ~ replacement therapy
in humoral- antibody- immunodeficiency
diseases.
Serum from horse~ therapy of tetanus,
snake bites, rabies etc.
immunoglobulins ~ prevention of graft
rejection
Importance of CMIR
Resist infection.
Induces unwanted immune response,
grafts or transplants.
Destroys tumour.
Fast in action to combat the invading
pathogens.
Failure/ deficiency of CMIR AIDS
Specific vs non- specific defence
system
Specific
 foreign body: act on
specific substances
 B & T memory cell
develop
 secondary response
 immunity can be
established
Non- specific
 eliminate all foreign
substances nonselectively
 no memory cell
 no secondary
response
 fight against
invading substances
in a fast fashion
 Both fight against invading foreign bodies
Immunity
Passive
Passive immunity in infants
~ antibodies from mother
 fetus
Artificial passive immunity
~ injection with
immunoglobulin
 short duration
Active
Naturally induced
~ natural encounter
 long duration
Artificially induced
~ immunization
 long duration
Characteristics of active immunity
Antigens are recognized by
Lymphocytes first before activating the
cells.
Specific antigen elicit the specific
antibodies production.
Memory cells can be established.
Naturally acquired immunity
A result of contact to diseases or
vaccination.
Achieved injecting small amount of antigen
(vaccine) into the body of an individual.
The small dose of antigen is safe.
The individual does not contact the
disease, but is stimulated to form
abtibodies against the antigen.
Booster injection is needed sometimes.
Vaccination
 Small dose of antigen is injected to the
individual.
 either killed or attenuated
~ not contact with disease
~ stimulated to manufacture antibodies
 Booster injection  quicker production of
antibody & long lasting immunity.
Types of vaccine
 Toxoids e.g. tetanus
~ a preparation of the poisonous material
that is produced by dangerous infective
organisms.
 Killed organisms e.g. dead influenza
viruses
 Attenuated organisms e.g. TB, measles,
poliomyelitis
~ modified but living organisms
 Infective agents of a related disease
e.g. smallpox
Duration of protection
Smallpox & polio vaccines  long lasting,
complete protection
BCG fairly long lasting, but not complete
protection
TAB typhoid rather temporary & partial
protection
Vaccines for special group
 Sex group
Young girls : German measles
 Age group
Young children : Polio, smallpox, measles,
cough
 Occupation
Medical workers: Hepatitis B
Sewage workers, field workers: Plague
 Traveller
Pros & cons of vaccination
Pros
Establishes active
immunity against
specific diseases
Cons
Induces
hypersensitivity in
some people
Unwanted immune responses
 Transfusion reaction
 Rejection of tissue transplantation
Blood transfusion
If a patient receives blood that is
incompatible, a type of unwanted immune
response occurs.
Agglutinogens( act as antigens) exist on
donor’s RBC membrane.
Incompatible agglutinated donor’s cell
Rejection of tissue transplantation
Transplantation ~ replacement of diseased tissues
or organs by healthy ones
 Foreign tissue acts as an antigen once inserted
into recipient  stimulates immune response in
the recipient
Rejection of transplanted tissue
Graft
CMIR of the host
Proliferation of killer cells
Enhanced phagocytosis
REJECTION
 Vascularisation between
grafts & the host
Methods to avoid/ minimize graft rejection
Tissue matching
~ graft between genetically identical
individuals are not rejected.
Immunosuppressive drugs
~ any drug inhibiting mitosis suppresses
the response.  More prone to cancer
X- irradiation
~ X -irradiation inhibits blood cell
production
 slow down rejection
Drugs used to treat infectious diseases
For example:
 Antibiotics
 Sulphonamides
Antibiotics
~ Organic compounds produced by microorganisms.
~ Able to kill or inhibit the activities of
other micro- organisms.
Action Inhibit cell wall formation
Destroy the selective
permeability of cell membrane
Interfere protein synthesis
Inhibit nucleic acid metabolism
Mechanisms of antibiotic resistance
 Inactivation of the antibiotics
 Absence of sensitive structures to antibiotics
 Presence of barrier to protect the cell
 Develop alternate metabolic pathway
Avoid antibiotics resistance
 Avoid overuse & indiscriminate use
 Use correct dosage of proper antibiotics
 Use different antibiotics once
micro-organism shows resistance
 Use combination of antibiotics
Non- medical use of antibiotics
 Growth stimulation
~ poultry & livestock
 Food preservation
~ preserve fresh meat
 Controlling plant
diseases
Sulphonamides
~ A group of chemical disturbing the
metabolism of folic acid in bacteria
Normal:
Para-aminobenzoic acid Folic acid
Normal growth of bacteria 
Presence of Sulphonamides:
Sulpha drug no folic acid produced
Bacteria will die 
Problems of drug therapy
 Induce the development of drug resistant strains of
micro-organism.
 Cause undesirable side effects.
 May not be used in some patients.
 Eliminate the normal micro-organism in patients’ guts.