Immunology Introduction

“This course is aimed at promoting an understanding by students of how organs, cells and
molecules are integrated into a functional immune system”
Objectives

 Understand gross anatomical organisation of the immune system and its constituent
components
 Discriminate between innate and adaptive immunity
 Understand the genetic basis for generation of diversity in receptors used for antigen
recognition
 Appreciate how cells utilize membrane-bound and soluble mediators to communicate
 Understand how cell surface events can be transduced and regulate proliferation and
differentiation
 Appreciate how dysregulation of the immune system can lead to pathology
 Gain insight into strategies for immunoprophylaxis

Key Terms

Polymorphic – Having many shapes / forms

Autoimmunity – The failure of an organism to recognise its own parts as ‘self’, allowing an immune response
against its own cells and tissues

Exogenous agent – An foreign body or infectious agent (derived from outside of the body)

Antigen – Any molecule that can stimulate an immune response and is recognised as foreign
 Must have a defined shape and structure

Antibody – A receptor that can recognise and bind to specific antigens

 A group of polymorphic glycoproteins

Innate immunity – The cells and mechanisms that defend the body from infection in a non-specific manner

Adaptive Immunity – A specialised and specific method of defence that provides the ability to recognise and
remember specific pathogens, generating immunity

Clonal Expansion – The production of many identical cells from a single ancestor cell

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Immunoprophylaxis - Prevention of disease by the administration of vaccines or hyperimmune sera

Introduction

Just an overview – everything will be covered in detail later on in the course

Studying immunology is important for human health. The immune system fights off infectious
diseases (exogenous agents) as well as combating its own abnormal cells such as cancerous and
neoplastic cells. Knowledge of the immune system is very important in fields such as organ
transplantation, where tissue rejection is a major issue.

Infectious diseases are still a huge burden on health

 e.g. Malaria, HIV, TB and helminths (worms)
 Predominantly an issue in developing countries
 Around 50% global population are infected with one or more of these agents

Some people are susceptible to infection, whereas others are resistant

Various individuals will have different proteins, so their immune responses will differ - this protects
the population as a whole

There are currently around 40 commercially available vaccines, most of which are quite old
Historical method of vaccination was to isolate a pathogen, kill it, then inject it into an individual

The major infectious diseases listed above are an issue because we have not been able to
produce vaccines against them and they have evolved to escape our immune system or supress
it. Some viruses evolve rapidly, such as influenza, so new strains form at a fast rate. This makes
it impossible to vaccinate against the influenza infection.

Autoimmunity:

Autoimmunity occurs when regulation of the immune system goes wrong, and the immune system
attacks its own cells and tissues.

Allergies and Asthma are examples of autoimmune disorders,

Their incidence in the developed world in the past 30 years has increased dramatically
These diseases are caused by hypersensitivity; the patient’s immune system is overactive

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This is due to the ‘hygiene hypothesis’

In this time frame there has been a huge decline in viral and bacterial infections
It is widely believed that these disorders are increasing because children have not been exposed
to enough infectious agents whilst growing up

An allergy is a hyperactive reaction to an antigen

Helminths supress the immune system. They are being used to treat patients with autoimmune
disorders

Two distinct parts of the immune system:

When coming across a pathogen for the first time, it takes time for an immune response

Innate immunity – an immediate response to a pathogen, even if it hasn’t been seen before
e.g. phagocyte ingesting a foreign body
It initiates specific, or adaptive immune responses

Adaptive immunity – expansion of a population of cells to fine-tune a response to a specific

pathogen. The structure of the receptors that recognise these foreign bodies is modified, then the
population of the cells that express these receptors is expanded. A form of immunological
‘memory’.

Key elements of the immune system:

1. Recognition / discrimination
The immune system must be able to recognise when something is wrong, at a molecular basis
Specific receptors have evolved to do this, antibodies are the main example
The immune system has to be able to discriminate between ‘self’ molecules and ‘non-self’

2. Regulation
What type of immune response needs to be initiated?
 e.g. Just make some antibodies or use certain cells etc.
What magnitude of immune response?
When to turn off immune response?
Issues with immunological regulation can result in autoimmune disorders

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3. Memory
Developing immunity to prevent recurring infections by the same pathogen
Some diseases will only affect an individual once, e.g. Chickenpox
Once infected, the individual will gain immunological memory of the virus that causes the disease,
preventing another infection.

B-cells:

B-cells make antibodies

They have membrane-bound receptors on their surface (antibodies)
Each antibody has a defined shape, it will bind to a specific antigen that it is complementary to
When the virus is encountered, the B-cell that has an appropriate antibody will be triggered and
clonal expansion will occur. Millions of b-cells will be generated with the same receptor.

 Some become effector cells – take care of the immediate infection

 Others become memory cells – a reproducing population of memory cells last a lifetime and
protect against future infections by the same pathogen

Antibodies:

A diverse set of glycoproteins that are secreted by plasma cells (a differentiated B-cell)

Complement:

A group of serum proteins that mediate inflammation and lysis

Consists of a series of proteolytic enzymes that form a cascade of activations resulting in an
amplified response

The two types of immunity:

1. Humoral immunity – Immunity regulated by soluble factors (antibodies & complement)

1st step of immune response

a) Causes inflammation
The complement causes an increase in vascular permeability

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 The blood vessels in the area become ‘leaky’

 Plasma + white blood cells can move into the surrounding tissue
Inflammation is painful due to the pressure exerted against nerve endings
Inflammation attracts cells to the site of infection / tissue damage (chemoattractant)
Stimulated by the complement as well as other factors

b) Causes lysis of bacterial cells

Some of the molecules involved can punch holes through bacterial cells

2. Cell mediated immunity – immunity that is affected by cells

 NK cells (natural killer)
 Cytotoxic T-cells
 Granulocytes
 Macrophages

Released antibodies will co-operate with cells in progression of the immune response

In reality, both are closely linked and require one another

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