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INNATEIMMUNITY
Dr. A. A. Wegdan
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Immunity
The main function of the immune system is to
prevent or limit infections by microorganisms.
The immune response can be:
a. Innate (natural or nonspecific).
a. Adaptive (acquired or specific).
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Innate (Nonspecific) Immunity
It is naturally occurring.
Non specific and includes:
Natural barriers to infectious agents.
Humoral proteins.
Phagocytosis and natural killer cells.
Inflammation and a variety of other
nonspecific factors.
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Mechanisms Of Innate Immunity
1- Physiologic (Natural) Barriers at the Portal ofEntry.
2- Humoral Proteins.
3- Phagocytosis.
4- Reaction to Infection.
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1- Physiologic (Natural) Barriers at the
Portal of Entry1- Skin
a) Intact skin.
b) Fatty acids and lysozyme.
2- The Respiratory Tract
a) The hairs of the anterior nares.
b) Respiratory cilia.
c) Cough and sneezing reflexes.
d) Surface phagocytes.
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1- Physiologic (Natural) Barriers at the
Portal of Entry3- The Conjunctiva
a) The blinking reflex.
b) The circulation of tears.
c) Lysozymes.
4- Gastrointestinal Tract
a) Normal flora of the buccal cavity and colon.
b) Low pH of the stomach.
c) The digestive enzymes.
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1- Physiologic (Natural) Barriers at the
Portal of Entry.
5- Genital Tract
a) The thick stratified epithelium of adult vagina
b) Normal flora and low pH of the vagina.
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1- Physiologic (Natural) Barriers at the
Portal of Entry.
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2- Humoral Proteins
If microorganisms succeed in overcomingthese natural barriers and be able to penetrate
inside the body, their growth will be limited by a
second strong line of defense:Humoral Proteins
The body's innate resistance to many pathogens
is provided by enzymes and other proteins in the
blood and tissue fluids.
These proteins are the effectors of humoral
innate immunity.
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2- Humoral Proteins
a) Lysozymes:digest the peptidoglycan ofbacterial cell wall.
b) Acute phase proteins e.g. C-reactive
protein, coagulation factors:participate inantimicrobial defense.
c) LPS-binding protein (LBP) and soluble
CD14:enhance phagocytosis.
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2- Humoral Proteins
d) Defensins:small peptides which can lysemicroorganisms directly.
e) Complement components (C3a, C5a):enhance the inflammatory response and
facilitate phagocytosis.
f) Interferons (alpha and beta): help control
of viral replication.
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3- Phagocytosis
A- Phagocytic Cells:
During bacterial infection, the number ofcirculating phagocytic cells often
increases. Types phagocytic cells:
1- Granulocytes (polymorphnuclear
leucocytes or neutrophils).
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3- Phagocytosis
2- Macrophages (circulating phagocytic
monocytes).
They are derived from monocyte stemcells in bone marrow and have a longer
life span than circulating neutrophils.
a) Blood monocytes.
b) Tissue macrophages; either wandering in
body spaces or fixed macrophages.
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3- Phagocytosis
Tissue macrophages
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Steps of Phagocytosis
a) Chemotaxis
The process by which
phagocytes are attracted
to the sites of
inflammation.
b) Ingestion (Engulfment)
Phagocytes engulf the
microorganism to form a
vacuole (phagosome).
c) Killing
1) Oxidative Mechanism.
2) Non-oxidative
Mechanism (lysosomes).
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Steps of Phagocytosis
c) Killing1) Oxidative Mechanism.
- Increased generation ofsuperoxide anions (O2).
- Increased release of H2O2.
- In the presence of oxidizingcofactors, acid pH and theenzyme myloperoxidase,H2O2 is converted tohypochlorite (HOCl) which is
an effective bactericidalagent.
2) Non-oxidative Mechanism(lysosomes).
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5- Reaction to Infection
1. Non specific reactions1. Inflammation:
Vasodilatation.
Oedema and swelling.
Migration of Polymorphonuclear cells.
2.Fever: The most frequent systemic manifestation.
Through the action of chemical stimuli on the
thermoregulatory center of the brain.a) Bacterial endotoxins.
b) Disintegrated leucocytes and tissue debris(endogenous pyrogens).
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5- Reaction to Infection
2. Specific reaction:
Through stimulation of the immunological
system.
Formation of specific antibodies and/or cell-mediated immunity.
This response helps in:
a) Recovery of the patient from the currentinfection.
b) Immunity against future re-infection.
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