This document summarizes a lecture on immunology. It discusses the components of the immune system including leukocytes, lymphoid tissues, and recognition of self. It describes innate immunity mechanisms like physical barriers and phagocytosis. Adaptive immunity involves humoral responses from B cells and cell-mediated responses from T cells. Immune disorders result from failures to distinguish self from non-self, like in autoimmune diseases, or from immunodeficiency, as in AIDS. The learning outcomes cover the immune system's structures, innate and adaptive immunity differences, innate immunity processes, adaptive immunity features, and immune disorder pathophysiology.

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Dr Alan Tuffery — Physiology Medical Science — 7 1
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Lecture 7 — Immunology
Structure
• Components
– Leukocytes
– Lymphoid tissue
– Recognition of self
• Innate Immunity
– Physical and chemical barriers
– Phagocytosis
– Inflammation
• Adaptive immunity
– Humoral responses (B cells)
– Cell mediated responses (T
cells)
• Immune Disorders
– Autoimmune diseases
– AIDS
Learning Outcomes
1. List the principal lymphoid
tissues and outline their roles
2. List the differences between
innate and adaptive immunity
3. Outline some key processes
of innate immunity
4. Explain some key features of
adaptive immunity
5. Explain the pathophysiology
of some immune disorders.
Dr Alan Tuffery — Physiology Medical Science — 7 2
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A network of cells and tissues that:
1. Defends the body against invading pathogens
2. Removes ‘worn-out’ cells
3. Destroys abnormal/mutant cells within the
body (e.g. control of cancer)
Immune System can also have harmful effects:
1. Allergies / autoimmune diseases
2. Tissue rejection.
Role of the Immune System (IS)

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Dr Alan Tuffery — Physiology Medical Science — 7 3
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FUNGUS
Epidermophyton
floccosum
(athlete’s foot)
VIRUS
Polio
PARASITE
Tapeworm
BACTERIA
Staphylococcus
aureus
(causes sepsis)
Infection-causing organisms (Pathogens)
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Components — White Blood Cells
Lymphocyte
– B cells - secrete
antibodies
– T cells - directly destroy
foreign cells
– Natural Killer cells - fight
viruses
Monocyte/macrophage
– Phagocytosis
– Secrete cytokines
(signalling molecules
other than antibodies).

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Dr Alan Tuffery — Physiology Medical Science — 7 5
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CENTRAL LYMPHATIC TISSUES
– Bone marrow - site of B cell development (and pre-
T cell)
– Thymus – site of T cell development
PERIPHERAL LYMPHATIC TISSUES
– Spleen
– Lymph nodes
– Gut-associated lymphatic tissue (GALT)
[Peyer’s Patches]
– Adenoids
– Appendix
– Tonsils.
Components — Lymphoid Tissues
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Components — self-recognition
Major Histocompatibilty Complex
• MHC on every (nucleated) cell
– Also known as human
leukocyte associated antigens
(HLA)
• Normally the body’s immune
system does not attack cells
that carry this ‘self’ marker
i.e. MHC
• No two individuals, except
identical twins, will ever
share identical MHC.
Transplant rejection
– Organ transplants and skin grafts
may be rejected due to presence of
MHC
– To minimise rejection, the MHC of
donor and recipient are matched as
closely as possible i.e. tissue typing
– Siblings usually provide the closest
match
– MHC do not play a role in transfusion
reactions because red blood cells do
not have MHC.

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Dr Alan Tuffery — Physiology Medical Science — 7 7
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Skin & mucous membranes
Phagocytosis
Inflammation
IMMUNE SYSTEM
INNATEINNATE IMMUNITYIMMUNITY
(non-specific; natural)
ADAPTIVE IMMUNITY
(specific; acquired)
HUMORAL-MEDIATED
(antibody mediated)
B cells
CELL-MEDIATED
T cells
Organisation of the Immune System
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Innate vs Adaptive Immunity
Innate
(Phagocytosis, Inflammation)
• Nonspecific
– Defends against any
pathogen upon first
exposure
– Responds to infectious
agents, chemical irritants,
tissue injury, burns
Adaptive
(Lymphocytes)
• Specific
– Responds to specific
pathogens on 2nd or
later exposure
– Comes into play after
nonspecific responses
have begun.

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Dr Alan Tuffery — Physiology Medical Science — 7 9
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• Initial & immediate response against invasion by a
variety of pathogens
• The response is rapid and non-specific
• Main mechanisms
1. Interferon, NK cells and complement system
2. Phagocytosis (by neutrophils & macrophages)
3. Inflammation.
Innate Immunity
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Innate — 1. Interferon, Natural Killer Cells
Interferon
• Released by virus-
attacked cells
• Protects other cells
from any virus
• Anti-cancer effects
– Slows cell division
– Enhances action of
NK cells and
cytotoxic T cells (qv)
Natural Killer cells
• Attack virus-
infected cells…
• …Cause lysis
• NB Both IF and NK
cells are non-specific
— any virus.

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Dr Alan Tuffery — Physiology Medical Science — 7 11
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Innate — 1. Complement System
Many very complex actions
• Innate response is recognition of micro-
organisms
• Lysis of invading micro-organisms
• Also reinforces other inflammatory
responses [hence name!].
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Innate — 2. Phagocytosis
Stages of Phagocytosis
1. Attachment
2. Internalisation (0.1 s)
3. Degradation
4. Exocytosis.
SEM macrophage engulfing bacteria
S&G. 23.3

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Innate — 3. Inflammatory Response
1. Bacteria enter tissue/damage
2. Release of histamine
– Increased blood flow
– Increased vascular
permeability
3. Increased leucocytes at site
Results
– Destroy or inactivate invaders
- Remove débris
- Prepare for healing & repair.
Atopic_Dermatitiswww.gcarlson.com
Animation of allergic (atopic) response
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Adaptive Immunity
1. Specificity
• Lymphocytes (B and T cells) bind and respond to foreign
molecules known as antigens via antigen receptors
1. Diversity
• The body possesses millions of lymphocytes that can recognise
and respond to millions of antigens (one each)
• Memory
• 1st exposure to an antigen generates lymphocytes & long-lived
memory cells – next exposure to the same antigen, memory cells
react more quickly & stronger response
• Self-Tolerance
• Lymphocytes can distinguish ‘self’ (our normal antigens) from
‘non-self’ (antigens from foreign material).

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Dr Alan Tuffery — Physiology Medical Science — 7 15
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Adaptive Immunity— humoral (antibody-mediated)
1. B Cells — Clonal Selection
• Antigen fits B cell’s receptors
• Proliferation and differentiation
into …
1. Plasma cells
• Produce antibodies in blood
• (immunoglobulins IgG, IgM, IgE, IgA, IgD)
• Short-lived
2. Memory cells (clone)
• With same receptor
• Long-lived.
S&G23.7(seeSherwood12-11)
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• T cells must become
activated before they
can attack pathogens
• The antigen is
‘presented’ to the T
cell by an ANTIGEN
PRESENTING CELL
(e.g. an infected
macrophage) via its
MHC
Adaptive — Cell-mediated Immunity

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• CYTOTOXIC T CELLS
– kill infected cells by lysis (direct action)
• HELPER T CELLS (~70% of T cells)
– secrete cytokines that enhance the activity of cytotoxic T cells;
enhance phagocytosis
– stimulate development of B cells into plasma cells (indirect action)
• SUPPRESSOR T CELLS
– secrete cytokines that suppress the activity of B cells, helper
T cells and cytotoxic T cells; inhibit phagocytosis.
Activated T cell enlarges & divides into:
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Adaptive Immunity
Natural
ACTIVE PASSIVE
Antibodies or
lymphocytes are
produced as a
result of infection
Antibodies are
passed to foetus
via placenta
or colostrum
Artificial
ACTIVE PASSIVE
Antibodies are
produced as a
result of
immunisation
with a vaccine
Antibodies that
have been produced
by another animal
or given artificially.
Adaptive Immunity can be
NATURALNATURAL or ARTIFICIALARTIFICIAL

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Dr Alan Tuffery — Physiology Medical Science — 7 19
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DISEASEDISEASE
• Systemic lupus
erythematosus (SLE)
• Rheumatoid arthritis (RA)
• Multiple sclerosis (MS) (p116)
SYMPTOMSSYMPTOMS
• fever, arthritis, mouth ulcers,
• inflammation and damage to
the cartilage and bone of joints
• T cells attack myelin:
Blurred vision,
Muscle weakness,
Ataxia
If immune system does not recognise its ‘self’ (e.g.
MHC), it reacts against normal cells and tissues
Immune Disorders – Autoimmune Diseases
Dr Alan Tuffery — Physiology Medical Science — 7 20
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• AIDS is caused by Human Immunodeficiency Virus (HIV)
• HIV binds to the surface of helper T cells and its nucleic acids
(RNA and DNA) enter the T cell
• Inside the cell, HIV uses the cell to make copies of itself
• HIV slowly destroys helper T cells in the body
(Helper T cells = 70% of all T cells)
• When T cell function is impaired, immune responses weaken and
other diseases develop.
Immune Disorders - AIDS

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Dr Alan Tuffery — Physiology Medical Science — 7 21
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SYMPTOMS
HIV Fatigue, fever, swollen glands, headache
AIDS Swollen lymph nodes, decreased T cell count;
Susceptibility to pneumonia and Kaposi sarcoma;
AIDS dementia
TRANSMISSION
Through blood, semen, vaginal secretions and breast milk.
Immune Disorders - AIDS
Dr Alan Tuffery — Physiology Medical Science — 7 22
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Learning Outcomes
1. List the principal lymphoid tissues and outline their roles
• Thymus (T cell dev.); Gut —B cells)
2. List the differences between innate and adaptive immunity
• Specificity, 1st exposure, cell-mediated, speed
3. Outline some key processes of innate immunity
• phagocytosis, inflammation, immune memory, self recognition)
4. Explain some key features of adaptive immunity
5. Explain the pathophysiology of some immune disorders.