The document summarizes the immune system. It discusses the organs of the immune system including primary organs like the bone marrow and thymus where immune cells develop and mature. Secondary organs where immune responses occur are also outlined, such as lymph nodes and spleen. The main cells of the immune system are described like lymphocytes (B cells, T cells, NK cells), phagocytes, dendritic cells, and granulocytes. The innate and adaptive immune responses are classified and the roles of antibodies and the complement system in immunity are summarized.

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
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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
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5. CLASSIFICATION
a) INNATE (non specific)
b) ADAPTIVE (specific)

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

8. ORGANS OF THE IMMUNE SYSTEM
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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
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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.
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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.
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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.
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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.
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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
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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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16. SPLEEN
Predominantly contains T-lymphocytes- 2/3
CD4+ and 1/3 CD8+
Follicles in spleen contains B cells

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.
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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.
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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
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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.
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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.
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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)
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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
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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.
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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
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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.
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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
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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
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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.
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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.
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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
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33. REGULATION OF IMMUNE RESPONSE

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
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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
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36. 36

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

38. Role of the antibodies
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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.
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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

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

46. THANK YOU FOR LISTENING