Lymphocytes precursors migrate from bone marrow to the thymus for processing to form “T” lymphocytes Processing in the thymus : Cells divide rapidly - Each cell develops specific reactivity for one antigen End result: thousands of T lymphocytes each with different specific reactivities for different antigens Insures that each T lymphocyte will not react with the body’s own antigens (self antigen) Then the processed cells leave thymus to lymphoid tissues Most processing of T lymphocytes occurs prior to birth and completed after birth T cells are activated for foreign cell attack when the cell express antigens on cell surface. Learn to recognize foreign antigens only in combination with a person’s own tissue antigens T cells respond to antigens only when they are bound to MHC proteins on the surface of antigen-presenting cells (macrophages, B lymphocytes, dendritic cells, somatic cells) 3 main types of T cells CD8 cells (cytotoxic, or killer T cells) Destroy host cells harboring antigen CD4 cells (mostly helper T cells) Modulate activities of other immune cells Secrete chemicals that amplify the activity of other immune cells Β-cell growth factor T-cell growth factor (interleukin 2) Macrophage-migration inhibition factor CD4+CD25+T cells / Suppressor T- cells( regulatory T cells)

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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