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IMMUNITY

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Learning outcomes
To recognize phagocytes and lymphocytes under the light
microscope
To describe the origin, maturation and mode of action of
phagocytes
To explain the meaning of the term immune response, making
reference to the terms antigen, self and non-self
To explain the role of memory cells in long-term immunity
To relate the molecular structure of antibodies to their
functions
To distinguish between active and passive, natural and
artificial immunity and explain how vaccination can control
disease
To discuss the reasons why vaccination has eradicated
smallpox but not measles, TB, malaria, sickle cell anemia or
cholera
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3

DEFENSE MECHANISM against
infection
Specific defense mechanism: identifies specific
pathogen to be destroyed; identity of pathogen
stored in memory immune cells; faster & more
effective response against future infection
Non-specific
defense
mechanism
(surface
membrane barriers & non specific cellular and
chemical defense): acts on various types of
pathogen; no memory

4

Skin & mucous membrane are
mechanical barriers preventing entry
of pathogen into body tissues (1st line
of defense)
Inflammation, phagocytes, natural
killer cells (NK cells), fever and
antimicrobial proteins (2nd line of
defense)
Skin effective barrier:
a
...
Secretion of sebum & sweat glands that
cover skin natural antibiotics to prevent
bacteria and mold growth
c
...
Dry habitat, lack of water few
pathogens can live
5

Mucous membranes cover inner surface of digestive
tract, reproductive tracts and respiratory tracts:
a
...

c
...


Trap & immobilize pathogens
Secrete hydrochloric acid to kill pathogens (stomach)
Secretes lysozyme enzyme together with saliva and tears
Produces an acidic secretion to prevent the growths of
pathogens (vagina)
e
...
Secretes chemicals to kill pathogens (intestines)

Urinating: clear urine tracts of pathogens

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7

NON-SPECIFIC CELLULAR &
CHEMICAL DEFENSE
2nd line of defense (phagocytes, natural killer cells,
complements , interferon, inflammation & fever) :
cellular counterattack
Phagocytes: macrophages & neutrophils swallow &
destroy pathogens in body
Natural killer cell (NK cells): lymphocytes that attack
tumours cells and virus-infected cells; destroy infected
cells by puncture the cell’s membrane, allow water enter
and cause cell burst
Complement system: activated by immune response
towards pathogens; form pores in cell wall of bacteria;
bind to pathogens, macrophage will identify and swallow
them
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9

Interferon: soluble protein secreted from infected cells;
activate macrophage and NK cells
Inflammation: triggered by inflammatory chemicals
released by injured tissue, phagocytes, lymphocytes and
complements in injured area
These chemicals stimulate vasodilation of capillaries to
increase blood supply to infected tissue; it also stretches
capillary wall to enable plasma protein, phagocytes and
complements to enter into injured tissue
Mixture of dead neutrophils, pathogens and dead cells
from injury site (pus)
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Inflammation
i
...
Destroy pathogens and residues of infected and injured cells
iii
...
youtube
...
youtube
...
5% of WBC are eosinophils, limited phagocytic
activity but contain destructive enzymes within
cytoplasmic granules; defense against parasitic invaders
such as worms
Natural killer cells do not attack microbes directly but
destroy the body own infected cells; not phagocytosis
but attack on membrane of the target cell (Immune System Natural Killer Cell
...
Neutrophil is attracted to bacterium by chemicals
released by bacterium
2
...
Pseudopodia form and engulf the bacterium to form a
vacuole (phagosome); the lysosome moves to vacuole
4
...
Bacterium is fully broken down and the products are
absorbed
http://highered
...
com/sites/0072495855/student_view0/chapter2/animation__phagocytosis
...
Phagocytes (especially
macrophages)
2
...
T-lymphocytes/T-cells
4
...
Mast cells

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3 types of lymphocytes found in human body are
B-cells, T-cells and NK cells
B-cells & T-cells are involved in immune
response; specific in action
NK cells are non-specific; bind to any cell
infected with virus and destroys it

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B-lymphocytes
Formed in bone marrow during embryonic stage
Matured @ bone marrow & moves into lymphatic
organs (lymphatic nodes & spleen)
Go through mitosis to produce new B-cells in lymphatic
tissues
B-cells are able to recognize antigen through protein
receptors on the surface of cells
B-cells attached to receptors will divided into plasma
cells that produces antibody

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T-LYMPHOCYTES
Formed in bone marrow during embryonic stage
Young T-cells move into thymus gland to mature &
differentiate into various types of T-cells
Similar shape as B-cells BUT unable to produce
antibodies
There are 4 types of T-cells
i
...
Cytotoxic T-cell
iii
...
Memory T-cell
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Helper T-cell: commander; bind to antigen presenting
cells, initiate response; trigger B-cells stimulation to
divide into plasma cells, produces antibody; activates
phagocytes
Cytotoxic T-cell: does not kill antigen BUT detects & kill
infected body cell; disabling pathogen from producing
cell
Suppressor T-cell: ‘brake’; dampens activity of T- & Bcells; regulate/halt cytotoxic T-cells action
Memory T-cell: ‘memory’; trigger immune response when
same antigen attack; exist for years
Immune System Animation
...
Humoral response or humoral immunity
(antibody)
B
...
Cell-mediated immune
response
1
...
Hydrolyzed into fragments by enzymes
3
...
Macrophage acts as antigen-presenting cell (APC)
5
...
Monokine such as interleukin-1 activates & stimulate
helper T-cell to bound to antigen-MHC to secrete
lymphokines/cytokine (interleukin-2)
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7
...
Interleukin-2 also activates NK cells & inducer T-cells in
thymus to mature
9
...
Response of producing a clone of T-cells to combact
antigen 1st entering body 1o response; memory T-cell
remain in the body for years to trigger 2o response when
same antigen attacks
Cell Mediated Immune Response
...

2
...


4
...
Clone of B-cells will then differentiate into plasma cells
that secrete large amount of antibodies
6
...
flv

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50

similarities
Memory capability
Specific
Arises from bone marrow (B-lymphocytes & Tlymphocytes)
Require antigen presenting cell (APC)
Require helper T-cell to detect presence of antigen

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52

ACTIVE IMMUNITY
Immunity resulting from exposure to an antigen
During subsequent immune response, antibodies are
produced by plasma cells
Enable memory cells provide ongoing long-term
immunity
There is delay before immune response is complete,
so immunity takes some days to build up
Permanent

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Passive immunity
Immunity involves the transfer of antibodies (already
made in body of another organism or in vitro) into
the body where they will bind to their specific
antigen if it is present
Provide instant immunity but does not lead to
development of memory cells
Thus, immunity only lasts for few weeks

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Natural immunity
Immunity that is required by individual as natural
part of their life
E
...
natural passive immunity following transfer
of maternal antibodies into fetus through the
placenta and into a newborn infant in the 1st milk
(colostrum)
E
...
natural active immunity following natural
infection by pathogen involving production of
memory cells (e
...
chicken pox)

55

Artificial immunity
Immunity that is acquired by a person as a result of
medical intervention
Includes artificial passive immunity following
injection of antibodies (e
...
monoclonal antibodies to
treat acute life-threatening infections such as
tetanus or rabies)
Includes artificial active immunity injection of
antigens (such as those attached to killed or
weakened pathogens) where memory cells are
made
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Summary of different
types of immunity
Active- body receives
antigen

Passive- body receives
antibodies

Natural

Natural activee
...
fighting infection

Natural passiveFrom mother via milk or
placenta

Artificial

Artificial activeArtificial passiveVaccination (injection of Injection of antibodies
antigens)

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58

VACCINATION
Also known as immunisation
Saved countless lives; effective to keep you stay well
(e
...
influenza vaccine, HPV vaccine and chicken pox
vaccine)
Administration of antigenic material (vaccine) to
stimulate adaptive immunity to a disease
Vaccine live but weakened forms of pathogens, killed
or inactivated forms of pathogens, or purified proteins
Smallpox vaccine was the 1st successful vaccine to be
developed; discovered by Edward Jenner, 1796

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How vaccines prevent
disease
Immune system recognizes
vaccine as ‘foreign’
Produces antibodies to fight
Memory cells prevent reinfection
Thus, slows down/ stops
disease outbreaks

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FAILURE OF VACCINATION
Improper storage
Temperature
UV light
Use after expiration
Attenuated vaccines need to be used soon after mixing
Improper administration
Improper timing (too early-maternal interference; too
late-already in disease process)
Primary vaccine failure (PVF): undetectable antibodies in
response to vaccination
Secondary vaccine failure (SVF): detectable antibodies
at 1st BUT fall with time
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Measles vaccine was shown short-lived immunity &
was discontinued 3 years after its introduction
Vaccines may cause problems for people with
certain allergies
...
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