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The immune system
1. THE IMMUNE SYSTEM
BY DR ALEYA REMTULLAH
FACILITATOR: DR NAHYA SALIM
8TH NOVEMBER 2016
2. TABLE OF CONTENTS
Introduction
Organs of the immune system
Cells of the immune system
Immune response
Organization of the body’s defenses
Complement system
References
PAEDIATRICS
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3. IMMUNITY
Refers to the relative state of resistance of the
host to infectious agents.
Protection against infectious diseases
Distinguishes ‘self’ from ‘non self’
Eliminates potentially destructive foreign
substances from the body
4. IMMUNE SYSTEM
Consists of cells and molecules
for immunity
IMMUNE RESPONSE
Is collective and coordinated response of
the immune system to the introduction of
foreign substances i.e resistance
PAEDIATRICS
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7. INNATE IMMUNITY ADAPTIVE IMMUNITY
Resistance to infection by virtue of
genetic/constitutional makeup
Resistance to infection acquired during life
Early response against microbes Delayed response
Immune response is non specific Immune response is highly specific
Memory effect absent Memory effect present
Response does not alter on repeated
exposure
Response improves with each successive
encounter by the same organism
Not affected by immunization or prior
exposure
Is improved by immunization
9. ANATOMY OF THE IMMUNE SYSTEM
The immune system is localized in several parts
of the body
immune cells develop in
the primary organs-
bone marrow and
thymus
immune responses occur
in the secondary organs
PAEDIATRICS
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10. PRIMARY ORGANS
These are organs where lymphocytes arise and
mature.
They are also organs where lymphocytes capable of
recognizing self antigens are deleted or inactivated
Include the bone marrow and the thymus in
mammals.
PAEDIATRICS
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11. PRIMARY ORGANS:
Bone Marrow
Has precursors of blood cells
All blood cells originate from a common
stem cell which becomes committed to
differentiate along particular lineage.
Cytokines stimulate proliferation and
maturation of precursor cells in the
bone marrow.
PAEDIATRICS
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12. The marrow is the site of maturation of
B-lymphocytes which develop from
progenitor cells.
Also has numerous plasma cells which
secrete antibodies.
Develops in peripheral lymphoid tissues
as a consequence of antigenic
stimulation of B cells and then migrate
to the marrow.
PAEDIATRICS
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PRIMARY ORGANS:
Bone Marrow
13. A bi-lobed organ situated at the anterior of
mediastinum
The gland is arranged into an outer, more cellular
cortex and an inner, less cellular medulla.
Immature lymphoid cells enter the cortex,
proliferate, mature and pass on to the medulla.
From the medulla, mature T lymphocytes enter
the circulation.
PAEDIATRICS
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PRIMARY ORGANS:
Thymus
14. SECONDARY ORGANS
Peripheral organs/tissue.
Sites where mature lymphocytes respond to
foreign antigens
Include lymph nodes, spleen, mucosa
associated lymphoid tissues and cutaneous
immune system.
In addition, poorly defined aggregates of
lymphocytes are found in connective tissues
and in virtually all organs except the CNS
PAEDIATRICS
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15. SECONDARY ORGANS:
Lymph Nodes
Follicles: Rich in B-cells
Primary follicles: have predominantly mature, resting B-
lymphocytes that have not been stimulated recently by
antigens
Secondary follicles: have antigen stimulated B-cells
Parafollicular area: Rich in T-lymphocytes mostly CD4+
cells with sparse CD8+ cells
Medulla: rich in lymphocytes, macrophages, dendritic
cells and plasma cells
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17. CELLS OF THE IMMUNE SYSTEM
Normally present as:
Circulating cells in blood and lymph
Anatomically defined collections in lymphoid organs
Scattered cells in tissues
Produced as one component of haemopoiesis.
PAEDIATRICS
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18.
19. CELLS: Lymphocytes
Specifically recognize and respond to foreign
antigens
As they mature, they begin to express antigen
receptors and become responsive to antigenic
stimulation
Consist of distinct subsets that are quite different
in their functions and protein products even
though they all appear morphologically similar.
PAEDIATRICS
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20. CELLS: Lymphocytes
B-Lymphocytes
Bone marrow derived.
Only cells capable of producing antibodies
Their antigen receptors are membrane
bound forms of antibodies which initiates
the sequence of B-Cells activation
This leads to the development of effector
cells that actively secrete antibody molecules
PAEDIATRICS
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21. CELLS: Lymphocytes
T-Lymphocytes
Precursors arise in bone marrow and migrate to
and mature in thymus.
Further subdivided into functionally distinct
populations of
Helper T-Cells
Cytolytic/Cytotoxic T-Cells.
Suppresant T-cells
Do NOT produce antibody molecules.
PAEDIATRICS
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22. CELLS: T- Lymphocytes
Recognize only peptide antigens
attached to proteins that are
encoded in the major
histocompatility complex (MHC) and
expressed on surfaces of other cells.
PAEDIATRICS
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23. CELLS: Lymphocytes
Therefore they recognize and respond to cell surface
associated antigens.
This causes helper T-Cells to secrete protein hormones
called cytokines
Cytokines promote the proliferation and differentiation
of T-Cells as well as other cells e.g. B-cell and
macrophages.
Cytokines also recruit and activate inflammatory
leukocytes.
Cytotoxic T-Cells lyse cells that produce foreign
antigens (e.g. bacterial cells, host cells infected with
viruses and other intracellular microbes)
PAEDIATRICS
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24. CELLS: Natural Killer (NK) Cells
Also called large granular lymphocytes
Resemble T cells but are distinct
Do not express markers for either T or B cells
Capable of lysing virus infected cells and tumor cells
PAEDIATRICS
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25. CELLS: Mononuclear Cells
Cells have a primary function of phagocytosis.
Secondary function of presenting antigen.
They include macrophages and monocytes
Originate in bone marrow.
After maturation and activation can achieve
varied morphologic forms.
PAEDIATRICS
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26. CELLS: Dendritic Cells
Are accessory cells for induction of
immune responses
Two types have been identified:
Interdigitating dendritic cells
Follicular dendritic cells
PAEDIATRICS
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27. CELLS: Granulocytes
Contain abundant cytoplasmic granules.
Often referred to as inflammatory cells because
they play important roles in inflammation and
natural immunity and function to eliminate
microbes and dead tissues.
Stimulated by T-cell derived cytokines and
phagocytose opsonized particles.
PAEDIATRICS
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28. CELLS: Granulocytes
Peripheral blood contains 3 types of granulocytes
classified according to staining characteristics of
their predominant granules.
Neutrophils
Eosinophils
Basophils
PAEDIATRICS
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29. CELLS: Granulocytes
Neutrophils
Largest cell population
Rapid response to chemotactic stimuli
Phagocytoses and destroys foreign particles
Can be activated by cytokines produced by macrophages
and endothelial cells.
Possess receptors for IgG and complement proteins
Migrate to and accumulate at sites of complement
activation.
Function as effector cells of humoral immunity
PAEDIATRICS
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30. CELLS: Granulocytes
Eosinophils
Growth and differentiation stimulated by T-Cell
derived cytokine (interleukin 5)
Express receptors for IgE antibodies
Effective at destroying infectious agents that
stimulate the production of IgE e.g. helminthic
parasites
Also abundant at sites of immediate
hypersensitivity (allergic) reactions, contributing
to tissues injury and inflammation.
PAEDIATRICS
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31. CELLS: Granulocytes
Basophils
Circulating counterparts of tissue mast cells
Express receptors for IgE
Interaction of antigens and receptor stimulate
secretion of granule contents (histamine), which
are chemical mediators of immediate
hypersensitivity.
PAEDIATRICS
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32. THE IMMUNE RESPONSE
Is a coordinated and collective response against
foreign substances
Cardinal features of the adaptive immune response
include
Specificity
Diversity
Memory
Discrimination of self from non-self
PAEDIATRICS
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34. ORGANIZATION OF THE BODY’S DEFENSES
Non-specific defenses: no need to identify
pathogen. Always present in the body.
Physical barriers
Inflammation
Interferons
Natural cell killers (NK cells)
Complement system
Specific defenses: Based on recognition of the
pathogen’s identity
Humoral immunity
Cell-mediated immunity
PAEDIATRICS
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35. SPECIFIC IMMUNITY: THE PLAYERS
Macrophages (antigen
presenting cell = APC):
phagocytize pathogens and
present antigens to helper-
T lymphocytes
Helper-T lymphocytes:
secrete lymphokines and
activate B and killer T
lymphocytes
B-lymphocytes: multiply
and specialize into plasma
cells secrete antibodies
Killer-T lymphocytes: kill
(through lysis) infected or
cancerous cells
PAEDIATRICS
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37. ANTIBODIES
Antibodies, also known as immunoglobulins, are
Y-shaped proteins that are produced by the
immune system to help stop intruders (antigens)
from harming the body
39. Types of antibodies
Antibody = Immunoglobulin = Ig
IgG Most abundant. mostly in blood, lymph. able to cross the
placenta
IgA Found in tears, milk, blood, lymph
IgM First antibody to be secreted. found in blood, lymph.
IgD Found in blood, lymph, on B-cells
IgE Found on mast cells, basophils, eosinophils. involved in allergic
reaction.
PAEDIATRICS
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40. COMPLEMENT SYSTEM
It is part of the immune system that enhances (complements) the
ability of antibodies and phagocytic cells to;
-Clear microbes and damaged cells from an organism
-Promotes inflammation, and
-attacks membrane.
It is part of the innate immune system
It can be recruited and brought into action by the adaptive immune
system
Consists of small proteins that are synthesized by the liver and
circulate as inactive precursors
41. Three biochemical pathways activate the complement
system: the classical complement pathway, the alternative
complement pathway, and the lectin pathway
Its activation must be tightly regulated to prevent it from
damaging host tissues.
Is regulated by complement control proteins.
Some complement control proteins are present on the
membranes of self-cells preventing them from being
targeted by complement.
42. Allergies
When the immune system responds to harmless
substances
Allergens – antigenic substances which do no real
harm
Allergens include house dust, animal skin, pollen,
house dust mite and its faeces
43.
44. Histamine causes blood vessels to widen and
become leaky.
Fluid and white blood cells leave capillaries.
The area of leakage becomes hot, red and
inflamed
45. REFERENCES
Understanding the immune system by Andrew E Thompson MD, University of
British Columbia
LIFE- the science of biology, seventh edition, blood cells.
Anatomy and physiology of immune system- semester 1 notes
www.wikipedia.com
www.worldofteaching.com/immunesystem
http://study.com/academy/lesson/what-are-antibodies-definition-function-
types.html