NS0401 Lecture 5
The Immune System
Learning Outcomes
• Explain what is meant by the term immunity
• Describe how the immune system works
• Explain the difference between Innate(non -
specific) and Specific immunity
• Explain the process of phagocytosis
• Consider how inflammation can protect the body
• Explore the rationale for immunisation
• Discuss factors that can impair our immune
system
Definition
Immunity is the recognition and disposal of foreign or “non – self” material that enters
the body.
Playfair & Chain (2009)
Immunology is the study of the immune system and its effects on the body and on
invading micro-organisms
Migliozzi (2013)
Organs of the immune system
The Lymphatic system
• Parallel system to the blood circulatory system
• Consists of lymphatic vessels, capillaries, nodes and encapsulated organs e.g. tonsils
and spleen
The Spleen
• The spleen - detects potentially harmful bacteria and creates white blood cells –
lymphocytes
The Thymus
• Situated in the chest
• Blood stem cells mature & segregate into various T cell lymphocytes and acquire the
ability to recognise “self cells” from “non self” cells
Bone marrow
• Contains stem cells (immature cells)
Peyer’s Patch
• Small masses of lymphatic tissue, predominantly in the Ileum
Appendix
• Rich in lymphoid cells. Can be removed without having an affect on the immune
system
What happens when we become
infected?
1. Awareness - the body needs to identify that it has been infected
before it can trigger a response
2. Immediate response- activity of cells
3. Delayed response - some infections can be resolved with the
innate system. However, it is usually accompanied by a new response,
involving new cells. This is called a Specific or acquired immune response
4. Destruction - The pathogen is eliminated
5. Immunity - If your body becomes infected with the same
pathogen, the reaction is milder or does not occur.
The immune system
Innate (Non – specific) Specific (Acquired)
Physical Chemical
barriers barriers Cell- mediated Humoral
(T cell (B – cell
lymphocytes) lymphocytes)
Mechanical
Blood cells
barriers
First line of defence
External innate defence
• Physical – Skin, mucosa, cilia,
mucus
• Chemical – Acids e.g. HCL in the
stomach, fatty acids e.g. sebum,
Lysozyme – in sweat, tears (used to
break down bacterial walls. Breast
milk
• Mechanical – coughing, blinking,
sneezing
• Blood Cells – neutrophils,
monocytes & macrophages,
eosinophils, mast cells
Internal Innate Defences
• Phagocytes
– The body uses a number of cells and chemicals to
protect itself…
– Phagocytes
– Natural Killer (NK) cells
– Proteins
– Fever
Phagocytes
• Macrophages - Big eaters
- Derived from white blood cells called monocytes
- All tissues contain macrophages. Plentiful in liver, lungs & spleen
- 1st on the scene
- Recruit other cells to help
- Live in the blood stream. When we become infected, chemical messages
are sent to the blood cells, who then leave the blood stream and enter the
infected tissue
• Neutrophils – most prevalent white blood cell. Become phagocytic when
encounter infected tissue
Phagocytosos
1. Attachment
2. Ingestion
3. Kill
Natural Killer ( NK) Cells
• 1-5% of white blood cells
• Present in blood & lymph
– Large granular lymphocytes
– Detect abnormalities such as the lack of “self”
– Not phagocytic
– Directly contact the target cell, inducing apoptosis (cell
death).
– Also secrete chemicals that produce an inflammatory
response
Interferon & Cytokines
• Cytokines
-Produced by more than one cell type
-Bind to the cell surface receptors on target cells and send messages to the
nucleus
• Interferons
- Are cytokines
- Stop viral replication by binding to receptors making them
resistant to infection
- Anti viral
The Compliment System
Innate Immune response Specific immune response
Oponization Pathogen is marked for
elimination
Movement of cells or
Chemotaxis organisms in response to
chemicals.
Inflammation
Apoptosis Cell death
Inflammation/ Inflammatory response
What causes an inflammatory response?
» Trauma
» Heat
» Irritation – contact with chemicals or other substances
» Infection
4 signs and symptoms of inflammation
» Swelling (oedema)
» Pain
» Heat
» Redness
» Immobilisation (?)
Inflammatory Response
Recognition Activation of Complement
of pathogen Macrophages system
Fever
• Fever, is a response to invading micro-
organisms.
• When Leukocytes and macrophages are
exposed to pathogens, they release pyrogens
• These act in the hypothalamus – raising the
body’s temperature above 37c
• Fever causes the liver to retrieve zinc & iron
• Increases metabolic rate – increases repair
process
Benefits of the inflammatory process
• Prevention of spread to other tissues
• Disposes cell debris and pathogens
• Prepares for repair of the damage (Marieb
2006)
• Alerts the adaptive immune system
Specific Immune System
Recognises
pathogen
Specific immune
response
Production of
T&B
Lymphocytes
What are lymphocytes?
B Lymphocytes (B cells) T Lymphocytes ( T cells)
• Humoral immunity • Cell mediated immunity
• start & complete maturation in • Start in the bone marrow, but
the bone marrow, mature in the Thymus
• have a life span of weeks, • Does not involve antibodies
• Involves other cells e.g.
• can travel anywhere macrophages, NK cells,
• Key to the production of cytokines
Glycoproteins • Help B lymphocytes make
(immunoglobulins) antibodies
• Bind to antigen of invading • Travel to where the pathogen
microbes is & get close to the antigen
Cytotoxic T Lymphocytes
• Important in viral infections
• Bind to target cells, releasing toxic substances
• Target cells may be viral, tumours or non self grafts.
E.g. kidney, heart transplants
• The infected cell and virus is destroyed
• Virus unable to invade other cells
How is the immune system controlled?
• T helper & T suppressor lymphocytes
• Coated with proteins which stimulate the
immune system (CD4)
• T suppressor cells prevent overstimulation
• Cytotoxic T cells may also be involved
Antigen Antibody
A foreign substance that can be A protein molecule that is released by a
recognised by the immune system plasma cell and binds to an antigen
and generates an immune response. Marieb & Hoehn 2013
Can be external or internal
Immunological memory
• Primary immune response – first exposure to an organism
can take 3-6 days. The time required for B cells to proliferate. Once B cells are
mobilised, plasma antibody levels rise – reaching peak levels around 10 days
• Secondary immune response – faster, more prolonged,
more effective because the immune system has already been exposed to the
antigen
• Cell memory - memory cells provide immunological memory. Persist for
months, years and even a life time. E.g. mumps, measles, chicken pox. Because of
cell memory, when exposed to the antigen again, the immune response will be
faster, ,ore aggressive and therefore you may get no or minimal symptoms
Antibodies
Neutralisation – some antibodies bind to viruses and bacterial toxins
forming a coating around them, rendering them harmless
Agglutination - clumping together of foreign bodies, ready for
phagocytosis bind to viruses and bacterial toxins forming a complete
coating
around them and rendering them harmless.
• some antibodies bind to viruses and bacterial toxins forming a
complete coating around them and rendering them harmless.
Types of Acquired immunity
Natural Artificial
Acquired by having the disease Vaccination - defined as ‘The
(clinical infection) or by having a process by which the adaptive
subclinical infection where the micro- immune system is primed to the
organism is present in the tissues antigens of a particular micro-
without causing the disease itself. organism so that a first infection
produces a secondary response’.
Maternal antibodies that are Antibodies or antitoxins obtained
transmitted across the placenta and in from human beings following
breast milk to the baby vaccination.
Fighting cancer
• T cells & antibody specific for tumour antigens
can be found in people with cancer.
• Blood tests can detect these antibodies e.g.
Prostate – Specific Antigen (PSA)
• Human Papilloma Virus (HPV) – this is associated
with cervical and some Head & Neck cancers, vaginal and anal
• Interferon treatments naturally made by our immune
system. Interferon-alpha is often used in treating chronic
myeloid leukaemia (CML). This reduces the growth and
division of leukaemia cells.
What factors can affect immunity?
Immunodeficiency
Congenital
• Severe combined immunodeficiency (SCID)
• HIV & AIDS – transmitted by body secretions, mainly blood, semen and vaginal
secretions. An infected mother can transmit virus to baby.
• Autoimmune Disease - where the immune system cannot distinguish between “self”
and “non- self”, and starts to attack itself.
• Rheumatoid Arthritis
• Myasthenia Gravis (impaired communication between nerves and skeletal
muscles)
• Multiple Sclerosis
• Type 1 Diabetes Mellitus
• Glomerulonephritis
• Acquired
• Hodgkin's Lymphoma – B cell cancer
• Immunosuppression drugs used in transplantation
• Cytotoxic drugs
Summary
• The immune system is a complex network of cells,
tissue, organs and chemicals
• They work collaboratively to identify and kill
pathogens
• Has the ability to identify and distinguish the body’s
own health cells (self) from foreign bodies (non- self)
• Many factors can affect immunity
• Understanding how our immune system works has
led to breakthroughs in the treatment of disease,
including some cancers
