This document provides an introduction to immunology and describes the key concepts of the immune system. It defines immunity and the immune system, explaining that the immune system protects the body from infectious agents and disease. It describes the structure of the immune system as a complex network of cells, tissues, and organs working together for defense. The main functions of the immune system are then outlined, including distinguishing self from non-self, defending against pathogens, removing dead cells, and remembering previously encountered pathogens. The concepts of immune tolerance and self-tolerance are also introduced.

1. Introduction to Immunology
Lecture 1
2nd stage
Hawler Medical University
College of Health Sciences
Medical Microbiology Dept.
Dr. Amer Ali Khaleel
(Medical Immunology)
amer.khaleel@hmu.edu.krd

2. Concept of Immunity:
• The word Immunology, which comes from the Latin = immunis = “exempt;”
English = protection from disease (resistance).
• So, Immunology is the study of the way in which body defends itself from
infectious agents.
• Immunity: The ability of an organism to recognize and defend itself against
specific pathogens or antigens. The cells and molecules responsible for immunity
constitute the immune system, and their collective and coordinated response to
foreign substances is called the immune response.

3. What is the Immune System?
• The Immune system is a biological structure and processes within an
organism that protects against disease by identifying and killing
pathogens and tumor cells.
• It detects a wide variety of agents, from viruses to parasitic worms,
and needs to distinguish them from the organism's own healthy cells
and tissues in order to function properly.

4. Structure of the Immune System:
• The immune system has a multilayered architecture with
defenses provided at many levels.
• The immune system is a complex network security system of
chemicals, cells, tissues and organs that work together to protect
the body.

5. The Functions of the Immune System:
•Without an immune system, a human being would be just as
exposed to the harmful influences of pathogens or other
substances from the outside environment to inside of the
body.

6. The main tasks of the body’s immune system are:
1. Classifying ability to distinguish between the body’s own cells (self) and foreign
cells (non-self).
2. It provides defenses against pathogens like bacteria, viruses, parasites or fungi.
3. Identifying-ability to distinguish one pathogen from another.
4. It removes (Scavenges) dead or worn out cells like RBCs.
5. It identifies and destroys abnormal cancer cells.
6. It protects against autoimmune diseases.
7. It rejects tissue cells with foreign antigens.
8. Remembering: The ability to remember previously encountered pathogens.
9. Switch on: The ability to respond when a pathogen invades.
10.Switch off: The ability to stop when danger passes.

7. Differentiation between self and non self substances:
•For protection to be effective it is important, however, that the
immune system can differentiate between “self antigen” and “non-
self (foreign)” antigen cell, organisms and all the biological,
chemical, physiological, metabolic, and physical aspects of the
immune response.
• Usually, the body should not work against its own healthy cells.

8. Differentiation between self and non self substances:
• All cells , as well as some particles such as pollen, display a unique
mix of macromolecules on their surfaces that the immune system
“senses” to determine if they are foreign or not. These chemicals are
called antigens. Because foreign cells or particles could potentially
enter through any number of portals, the cells of the immune system
constantly move about the body, searching for potential pathogens.
This process is carried out primarily by white blood cells, which have
been trained to recognize body cells (so-called self) and differentiate
them from any foreign material in the body, such as invading
microorganism cells (non-self).

9. Figure: Search, recognize, and destroy is the mandate of the immune system.
White blood cells are equipped with a very sensitive sense of “touch.” As they
travel through the tissues, they feel surface markers that help them determine
what is self and what is not. When self markers are recognized, no response
occurs. However, when non-self is detected, a reaction to destroy it is mounted.

11. Differentiation between self and non self substances:
• The immune system is designed to defend the body against foreign or
dangerous invaders including: -
1. Microorganisms (commonly called germs) such as bacteria, viruses,
fungi (yeasts and molds) & parasites (such as worms).
2. Innocuous (not harmful or offensive) substances (such as allergy).
3. Transplanted organs and tissues.
4. Cancer cells.

12. Differentiation between self and non self substances:
• Many autoimmune disorders are a result of the immune system
mistakenly attacking the body’s own tissues and organs. For example,
in rheumatoid arthritis, the body attacks its own joints and tissues,
causing pain and loss of function.

13. • The immune system can be activated by many “non-self”
substances. These are called antigens (Ag). The proteins on the
surfaces of bacteria, fungi and viruses, for example, are all
antigens.
• When the antigens bind to, for example, special receptors on
the defense cells, a series of cell processes is started. Then the
immune system can recall stored “memories” in order to more
quickly be ready to defend against known pathogens.
Differentiation between self and non self substances:

14. The state of unresponsiveness of the immune system
to antigen.
Or
A state of unresponsiveness to a specific antigen or
group of antigens to which a person is normally
responsive.
Immune Tolerance:

15. The state of unresponsiveness of the immune system to self-
antigen.
Or
The physiological state that exists in an organism when its
immune system has proceeded far enough in the process of
self-recognition to lose the capacity to attack and destroy its
own bodily constituents.
Self-Tolerance:

16. + There is immune response
- There is no immune response
LEAD TO
* Apoptotic cells is a form of programmed cell death.
* Homeostasis Maintaining a stable internal condition is
crucial to any form of living thing.

17. (irregular)

18. Terminology:
CD nomenclature:
• CD stands for cluster of differentiation. This is a classification
system for the different antigenic determinants found on cells. The
surface molecules of different types of cells and so act as markers of
differentiation. The different CD complexes are given a number to
differentiate them.
• Well over 300 CD molecules have been named.
• Many CD molecules, or CDs for short, are involved in the immune
response.

20. The Role of Markers and Receptors in Presentation and
Activation:
• All cells both foreign cells and “self” cells have a variety of different
markers on their surfaces, each type playing a distinct and significant
role in detection, recognition, and cell communication.
• Cell markers play important roles in the immune response, serving to
activate different components of immunity. Because of their
importance in the immune response.

21. Any Questions
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Cells Of The Immune System