Transcript First, Second Line Immunity

Immunity
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Aims:
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Must be able to define the term immunity.
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Should be able to outline the different forms of
immunity.
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Could be able to outline the stages of nonspecific immunity.
Basics
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Immune system differentiates between ‘SELF’ and ‘NONSELF’.
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‘SELF’: material made by the body’s cells.
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‘NON-SELF’: foreign material, includes material such as
snake venom, dust, pollen, viruses and micro-organisms,
such as bacteria.
If infected with foreign material, the immune system is
activated - attempts to remove the foreign material before it
causes harm to tissues in the body.
Two Types of Immunity
The two kinds of response of the immune system interact
together to provide immunity for an individual:
1.
NATURAL / INNATE immunity
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non-specific
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it acts in the same way for
every infection
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involves many physical and
chemical barriers to infection
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it has no ‘memory’ of a prior
infection
2.
Acquired or adaptive immunity
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highly specific
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involves the production of
specialised cells and
chemical substances known
as antibodies
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has a ‘memory’
Non-Specific Immunity
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First Line of Defence – Prevent entry to the body
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Skin – continuous barrier to microbe entry
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Mucous Membranes – Secreted by cells in respiratory
system – trap bacteria and swept by cilia – swallowed,
sneezed, coughed
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Natural Secretions – Tears, Saliva contain lysozyme
causing bacteria to burst. Stomach contains acid. Also
bacterial agents in Milk and Semen.
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Natural Flora – Bacteria found on skin in gut and in vagina,
non-pathogenic in given areas – inhibits the growth of
pathogenic bacteria.
Non-Specific Immunity
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Second Line of Defence – Kicks in after microbe entry
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Made up of a number of parts:
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Phagocytes and Killer Cells –
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Complement Proteins –
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Interferon –
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Cytokines –
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Inflammation -
The Second Line of Defense
A range of nonspecific defenses
inside the body
inhibit or destroy
pathogens.
These non-specific
defenses react to
the presence of
any pathogen,
regardless of which
species it is.
White blood cells
are involved in
most of these
responses.
The 1st line of defense
The 2nd line of defense
Eosinophils:
Produce toxic proteins
against certain
parasites, some
phagocytosis
Antimicrobial
substances
Inflammation
and fever
40°C
37°C
Phagocytic
white
blood cells
Basophils:
Release heparin and
histamine which
promote
inflammation
Neutrophils, monocytes:
These cells engulf and
destroy foreign material
(e.g. bacteria)
The 3rd line of defense
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Mast Cell
- Secretes
hisatmines
phagocytes
Phagocytes
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Phagocytes respond by engulfing and destroying microorganisms and foreign materials.
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Phagocytes are produced by cells in the bone marrow and
include neutrophils and monocytes/ macrophages.
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(When monocytes leave the bloodstream, they become
macrophages)
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A bacterium or other micro-organism is engulfed by a phagocyte.
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Enzymes and other factors are released into the vacuole
containing the bacterium and the bacterium is killed.
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Some white blood cells that kill virus-infected body cells are
called natural killer (NK) cells.
The Action of Phagocytes
Phagocytes are white blood cells that ingest microbes and digest
them by phagocytosis.
Detection
Phagocyte detects microbes by
the chemicals they give off
(chemotaxis), and the microbes
stick to its surface.
Microbes
Nucleus
Ingestion
The phagocyte wraps
pseudopodia around it
the microbe, engulfing
it and forming a vesicle.
Phagosome
Lysosome
Phagosome forms
A phagosome (phagocytic
vesicle) is formed, enclosing the
microbes in a membrane.
Fusion with lysosome
Phagosome fuses with a
lysosome (containing
powerful enzymes that
can digest the microbe).
Digestion
The microbes are broken
down by enzymes into
their chemical
constituents.
Discharge
Indigestible
material is
discharged from
the phagocyte.
Microbial Abuse of Phagocytes
Microbes evade
immune system
Some microbes kill
phagocytes
Dormant microbes
hide inside cells
Some microbes evade the
immune system by entering
phagocytes. The microbes
prevent fusion of the
lysosome with the
phagosome. They multiply
inside the phagocyte, almost
filling it.
Some microbes produce
toxins that kill phagocytes.
Some microbes can
remain dormant inside
the phagocyte for
months or years at a
time.
e.g. Chlamydia, Shigella,
Mycobacterium tuberculosis,
and malarial parasites.
e.g. toxin-producing
staphylococci and the
dental plaque-forming
bacteria Actinobacillus.
e.g. the microbes that
cause brucellosis and
tularemia.
Complement Proteins
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Blood proteins called complement proteins assist
phagocytes to recognise foreign material.
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In the second line of defence:
1.Some stick to invading micro-organisms that then
become more readily identifiable as foreign to
phagocytes.
2.Some stimulate phagocytes to become more active.
3.Some attract phagocytes to the site of infection.
4.Other complement proteins destroy the membranes of
invading micro-organisms.
Complement proteins:
bacteria
Complement protein
bacteria
Interferons
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Some virally infected cells secrete interferons.
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Induce resistance to viral infection in the surrounding cells.
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Acts as a warning signal from the cell already doomed
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Causes changes in the surfaces of the surrounding cells,
making it more difficult for a virus to infect
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Play an important role in reducing or slowing down the growth,
reproduction or development of the pathogen and minimising
the symptoms that arise
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Prevents viral protein synthesis
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Cytokines
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A group of proteins and peptides that are used in organisms as
signaling compounds.
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These chemical signals are similar to hormones and
neurotransmitters and are used to allow one cell to communicate with
another.
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Cytokines are involved in a variety of immunological, inflammatory
and infectious diseases.
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Each cytokine binds to a specific cell-surface receptor.
Inflammation
Damage to the body’s tissues caused by physical agents (e.g. sharp
objects), microbial infection, or chemical agents triggers a defensive
response called inflammation.
Usually characterized by four symptoms: pain, redness, heat, and
swelling.
The inflammatory response is beneficial has the following functions:
To destroy the cause of the infection and remove it and its
products from the body.
If this fails, to limit the effects on the body by confining the
infection to a small area.
To replace or repair tissue damaged by the infection by
improving blood flow.
The Process of Inflammation
Bacteria entering on
knife or other sharp
object.
Blood clot forms
Epidermis
Chemicals released by
damaged cells (e.g.
histamines and
prostaglandins) attract
phagocytes to the infection.
Dermis
Subcutaneous
tissue
Blood vessels increase in
diameter and permeability in
the area of damage. This
increases blood flow to the
area and allows defensive
substances to leak into tissue
spaces.
An abscess starts to form after
a few days. This collection of
dead phagocytes, damaged
tissue and various body fluids is
called pus.
Phagocytes reach the damaged area
within one hour of injury. They squeeze
between cells of blood vessel walls to
enter the region and destroy invading
microbes.
Fever
A fever (pyrexia) is defined as a body temperature above 37°C
(98.6°F) measured in the mouth.
Normal body temperature range is:
36 to 37°C / 96.8 to 98.6°F
Fevers are usually caused by bacterial or viral infections.
Fevers of less than 40°C (104°F) do not need treatment.
Excessive fever requires prompt attention as death usually
results if body temperature rises above 44.4°C to 45.5°C
(112°F to 114°F).
The Cause of Fever
Infection by pathogen or toxin
Macrophages respond.
The presence of endotoxins induces
the macrophage to produce a small
protein called interleukin-1.
Macrophage
Bacterium
Bacterial
toxins
Macrophage
releases interleukin1 into the blood
stream.
Hypothalamus
Thermostat is reset Interleukin-1
induces the hypothalamus to increase
production of prostaglandins.
This resets the body's 'thermostat' to
a higher temperature, producing
fever.
Temperature increases
beyond the normal range
of 36.2–37.2 °C (96.8–98.6 °F)
The Stages of a Fever
Fever Onset
The body responds to the new thermostat
setting, raising the body temperature by:
• Blood vessel constriction
• Increased metabolic rate
• Shivering
Chill Phase
Even though the body temperature is increasing above normal, the skin remains cold, and shivering occurs.
This condition, called a chill, is a definite sign that body temperature is rising.
When the body reaches the setting of the thermostat, the chill disappears.
Crisis Phase
Body temperature will be maintained at the higher setting until interleukin-1 has been eliminated.
As the infection subsides, the thermostat is then reset to 37°C.
Heat losing mechanisms, such as sweating and vasodilation cause the person to feel warm.
This crisis phase of the fever indicates that body temperature is falling.
The Benefits of Fever
Up to a point, fever is beneficial. Fever has the following effects:
Intensifies the effect of interferons (antiviral proteins that
inhibit viral replication).
Increases the production of T cells.
Speeds up the metabolic reactions, which helps to increase
the rate of tissue repair.
Increases heart rate, so that white blood cells are delivered to
sites of infection more rapidly.