Download Immunology Lecture 1

Immunology Lecture 1
WEEK 1
ACADEMIC YEAR 2015-2016
INTRODUCTION AND OVERVIEW
What Is Immunology?
Immunology is the science that studies the
immune system.
WHAT THE IMMUNE SYSTEM DOES?
The major functions of the immune system are:
1 – Protection of the body against damage
caused by infectious agents or any other
foreign substance in its environment.
2 – Removal of damaged tissues or cells
(Homeostasis).
3 – Check for development of unwanted cells
(altered or modified cells) within the body and
coordinate its removal (Surveillance)
WHAT DOES IMMUNOLOGY AIM FOR?
To give answers the following questions:
1 – How does the body defend itself from pathogens?
2 – How is a pathogen that succeeded in entering the
body, eliminated?
3 – How does the body remember a prior exposure to a
pathogen then responds faster and more efficiently
when the same pathogen is again encountered?
4 – How to make use of all these studies:
To develop vaccines and immune-therapies.
AGAINST WHAT THE IMMUNE SYSTEM IS ACTIVE?
Against foreign substances e.g. microbes, while
sparing the body’s own tissues.
This means:
1 - Ability to detect (recognize) the foreign
substance
2 - Ability to remove (eliminate) this foreign
substance.
Important definitions
The reaction against a microbe or any other foreign
substance is called immune response.
The lack of reactivity to self components is called
self tolerance.
Any substance that can be recognized by the
immune system and induce an immune response
is called antigen or immunogen.
Components of our own tissues can be
immunogenic in other hosts so they are called
self antigens.
WHAT IS THE STRUCTURE OF THE IMMUNE
SYSTEM?
A complex network of:
Cells
Tissues
& Soluble Molecules.
Cells of the immune system
The cells are widely distributed throughout the
body but occur predominantly in lymphoproliferative tissues e.g. bone marrow, thymus,
spleen, lymph nodes.
All immune cells arise from a stem cell in the
bone marrow. They are mainly leukocytes.
All immune cells have the ability to recognize and
eliminate injurious substances
Molecules
A wide variety of molecules are involved e.g.
Antibodies
Cytokines
Acute phase proteins
Complement
Adhesion molecules
Functionally, the immune system is divided into 2 complementary units:
1 – The innate immune system: the 1st to
interact with invaders, and it is fast.
2 – The adaptive immune system: deals with
invaders that escape destruction by innate
mechanisms.
HOW DOES THE IMMUNE SYSTEM DISTINGUISH BETWEEN SELF
ANTIGENS AND FOREIGN ANTIGEM]NS?
HOW IT DOES DISTINGUISH BETWEEN DIFFERENT ANTIGENS?
The immune system can recognize chemical
differences between macromolecules
(molecular recognition).
This very important property is achieved
through receptors on the surface of immune
cells.
HOW DOES THE IMMUNE SYSTEM ELIMINATE PATHOGENS?
Through different effector mechanisms that
handle a wide range of organisms causing
different types of infections.
These mechanisms differ according to the
location (lifestyle) of the organism:
intracellular or extracellular.
EXAMPLES OF EFFECTOR MECHANISMS
1 – Neutralisation by specific antibodies
2 – Phagocytosis by phagocytic cells
3 – Use of complement system
4 – Cytotoxic reactions
5 - Inflammation
PROTECTION IS AT SEVERAL LEVELS
1 – External defenses (barriers to infection)
2 – Innate immunity
3 – Adaptive immunity
Always remember:
Infection does not necessarily mean disease. Why?
Because the immune system in most cases is able to
eliminate infection before disease occurs.
Disease occurs only when:
1 – The infectious dose is so high
2 – The virulence of the organism is great
3 – Immunity is compromised
Always remember:
For the most part, the immune system has
beneficial effects.
However, there can be some bad effects as well,
Example:
During inflammation, there may be local
discomfort and some damage to healthy
tissues.
WHAT HAPPENS IF THE IMMUNE SYSTEM MALFUNCTIONS?
When immune mechanisms fail
Immunopathology.

The immune system may fail in one of 3 ways:
1 – When any of its components is defective,
this is called immunodeficiency .
2 – When the immune system reacts against self
antigens, this is called autoimmunity.
3 – When an exaggerated response occurs in
certain individuals to harmless environmental
antigens e.g. pollens, this is called Allergy or
hypersensitivity reactions.
Other situations: when the immune system acts
normally but responses are inconvenient
In graft rejection