This document provides an introduction to the immune system, detailing the differences between innate and adaptive immunity, as well as the components and phases of the immune response. It covers the role of physical and chemical barriers, inflammatory responses, cytokines, and the complement system in innate immunity, along with the specific mechanisms of adaptive immunity through B and T lymphocytes. The document also discusses how active and passive immunity function, including examples and characteristics of memory in immune responses.

1. INTRODUCTION TO IMMUNITY
Dr. Nisreen Daffa Alla
M.B.B.S, PhD (Human Physiology),
MSc health Profession Education
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2. OBJECTIVES
The student should be able to:
 Discuss general overview of the immune system.
 Differentiate between innate and adaptive immunity.
 Identify the component of innate and adaptive immunity.
 Define the term antigen, antibody and hapten.
 Phases of immune response.
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3. IMMUNITY
• Body’s ability to resist or eliminate potentially harmful
foreign materials or abnormal cells.
• Immune system activities
– Defends against invading pathogens.
– Removes cells and tissue damaged by trauma.
• Immune surveillance.
– Identifies and destroys abnormal or mutant cells that
have originated in the body.
– Mounts inappropriate immune responses that lead
either to allergies or to autoimmune diseases.

4. 4
Immunity
Innate Adaptive
Active
Cellular Humoral
Passive

5. INNATE IMMUNITY
Innate/Non-specific/Natural Immunity:
 Nonspecific
Non-selective defend against foreign invaders
 Natural
Present in most people without prior exposure
to antigen
Responses work immediately when body is
exposed to threatening agent
First line of defense
 Limited responses
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6. INNATE IMMUNITY
Innate immunity Include:
1. Barriers
– Physical
– Chemical
2. Defensive cells
– Neutrophils
– Macrophages
– Natural killer cells (NK)
3. Chemical defenses
– Cytokines
– Complement system
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7. Physical and chemical barriers
• Skin:
- continuous, impassable barrier to infectious pathogens.
- skin’s acidity.
- beneficial microorganisms that coexist on the skin compete
with invading pathogens, preventing infection.
 Eyes and mucus membranes:
- tears and mucus secretions that trap and rinse away
pathogens
- cilia in the nasal passages and respiratory tract that push the
mucus with the pathogens out of the body.
- low pH of the stomach (which inhibits the growth of
pathogens
- the process of urination (which flushes pathogens from the
urinary tract).
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8. INFLAMMATION &NEUTROPHILS AND
MACROPHAGES ACTIVATION
• Inflammation: a protective response
involving immune cells, blood vessels, and
molecular mediators. The function of
inflammation is to eliminate the initial cause
of cell injury
• Neutrophils and macrophages are recruited to
the sites of injury: these cells kill
microorganisms/damaged cells by phagocytosis
.
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9. Cytokines
• Low molecular weight proteins (30 KDa)
• Produced by white blood cells
• Cytokines regulate immune responses

10. INTERFERON(CYTOKINE)
• α, β, and γ interferon.
• Released by virus
infected cells.
• Function by blocking
viral reproduction.
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11. COMPLEMENT SYSTEM
Series of ~ 30 proteins
Activated by
microorganisms/ immune
complexes
Functions:
1. Cytolysis
2. Opsonization
3. Activation of inflammation
4. Chemotaxis
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Continued next
page…
Classical
Pathway
Alternative Pathway
Mannose
Binding Lectin
(MBL) Pathway
Antigen-
Antibody
complex
Activating
surfaces
Pathogen
surfaces
C
1
C
4
C
2
C3
b
C
4
C2
MBL
MASP-
1
MASP-
2
C3 Convertase
C3b
C3b
C3a
C3
C5b-9
C5a
C5
C5 Convertase
Lytic
Pathway
C5b
C6
C7
C8
C9
Membrane attack
complex (MAC)
Anaphylatoxin
Activates mast cells
Chemotactic
Facto
r B
Facto
r D
Facto
r H
Facto
r I

12. ADAPTIVE IMMUNITY
• Adaptive or Acquired immunity
– Specific: Specifically targets foreign material to which
body has already been exposed
– Late: Body has taken time to prepare to attack
– Efficient:
o Ultimate weapon against most pathogens
o Responses are mediated by β and T lymphocytes
o Formation of memory cells allows system to react
more swiftly against specific invaders in the future

13. ADAPTIVE IMMUNITY
Two types:
1. Active immunity – direct encounter
with the antigen.
2. Passive immunity – without
encounter with the antigen
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14. ADAPTIVE IMMUNITY
• Active immunity
– “self-generated”
– Results from exposure to an antigen.
– Encounter with the antigen can be:
o Natural when you get the disease
o Artificial: Vaccination
• Passive immunity
– “borrowed immunity”
– Results from transfer of preformed antibodies
– Can provide immediate protection
– Natural: Example of passive immunity is transfer of
IgG antibodies from mother to fetus
– Artificial: Tetanus toxins, anti snake venom, rabies
virus

16. ADAPTIVE IMMUNITY
• Antigen – “any substance when introduced into
the body stimulates immune response
– Bacteria, fungus, parasite
– Viral particles
– Other foreign material
• Pathogen – an Antigen which causes disease.
• Hapten – is not antigenic by itself. When combines
with protein it become an antigen
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17. B AND T LYMPHOCYTES
• Mainly produced from lymphoid
colonies in lymphoid tissues
• Lymphoid tissues
– Tissues that produce, store,
or process lymphocytes
– Include
• Bone marrow
• Lymph nodes
• Spleen
• Thymus
• Tonsils
• Adenoids
• Appendix
• Peyer’s patches (GIT)

18. Bone Marrow
Pre-B
Cell
Pre-T
Cell T-Cell
T-suppressor
T4-helper
B-Cell Plasma Cell
IgG IgA IgM IgD IgE
Interactions between T- and B-Cells
T8-cytotoxic
T- memory Cell
B- memory Cell
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19. PHASES OF IMMUNE MECHANISM
Initial phase
– Entry of antigen and its contact with the specific receptor
on lymphocytic membrane.
Central phase
– Cooperation among different subset of lymphocytes that
proliferate and differentiate to form T & B lymphocyte +
memory cells
Effector phase
– Inactivation of antigen by sensitized T & B lymphocytes
Declining phase
-After eradication of the microorganism, the activated cells died
and small proportion remain as memory cells
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20. Characteristic of adaptive immunity
• Memory:
Two types of immune response:
- Primary immune response
- Secondary immune response

21. Phases of immune response

22. Class questions
Acquired
immunity
Innate
immunity
Specific/non specific
Rapid/late
Limited/ efficient
Memory
Barriers/cells/chemicals
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23. Class questions
What is the type of immunity in each case?
Person receive corona vaccine
Person bites by a dog. He received anti-rabies
antibodies
Child receive Ig A antibodies from his mother
milk
Person who got corona infection
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24. REFERENCES
 Human Physiology, Lauralee Sherwood, seventh
edition.
 Text book Physiology by Guyton &Hall,11th edition.
 Text book of Physiology by Linda S. Contanzo,
third edition.
 Physiology by Berne and Levy, sixth edition.
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