White blood cells (WBCs) or leukocytes are the mobile units of the immune system that help protect the body from infection and disease. There are two main types of WBCs: granulocytes which have granules in their cytoplasm and include neutrophils, eosinophils, and basophils; and agranulocytes which do not have granules and include lymphocytes and monocytes. Each type of WBC has a specific function such as phagocytosis, antibody production, or regulation of the immune response. Together, WBCs provide a powerful defense mechanism against infections, tumors, and toxins.

1. White Blood Cells
(WBCs)
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2. At the end of the session the students should
be able to:
Describe the different types of WBCs.
Explain the development of leucocytes
(leucopoiesis).
Discuss the function of different types of
WBCs.
Describe the mechanism of phagocytosis.

4. WBCs (leukocytes)
The leukocytes are the mobile units of the immune system.
• count: 4000 – 11,000 /mm3 .
Types:
Granular leukocytes:
– Neutrophil 60 – 70%
– Eosinophils 1 – 5%
– Basophils 0.5 – 1 %
Agranular leukocytes:
– Monocytes 3 – 8 %
– Lymphocytes 20 – 30 %
Life span of leukocytes:
- The average life span for granulocytes is 4 – 5 days.
- The lymphocytes & monocytes may live for months even years.
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6. Pathologic variation in leukocytic count:
1- Leukopenia:
• -  wBCs count below 4000 cell /mm3
• - Found in enteric fever.
2- Leukocytosis:
• - Means ↑WBCs count above 11,000 cell / mm3.
3- Agranulocytosis:
• - Acondition in which bone marrow stops WBCs production.
• - It's due to drug toxicity or irradiation.
4- Leukaemias:
- It's malignant disease of bone marrow → uncontrolled production of WBCs
(very high number).
- The leukaemic cells are non functioning & can't protect the body.

7. Leukocytes
WBCs
4 – 11 x 103/mm3
Granulocytes Agranulocytes
Monocytes
3 – 8 %
Lymphocytes
20 – 30 %
Neutrophils
60 – 70 %
Basophils
0.5 – 1 %
Esinophils
1 – 5 %
B lymphocytesT lymphocytes
T helper
Plasma
cells
T
suppresso
r
T
cytotoxic
macropha
ges

8. Functions of leukocytes
WBCs provide the body with a powerful defense
mechanisms against:
– Infections (viral, bacterial, parasitic or fungal).
– Tumours
– Toxins
They act together in different ways to prevent diseases
as by:
– Phagocytosis
– Formation of Sensitized lymphocytes
– Formation of antibodies

9. Neutrophils
Count: 60 – 70 % of TLC
Histology:
– Diameter:
• 10 – 12 µm
– Cytoplasm:
• contain small granules stained with both acidic and basic dyes (so called
neutrophils)
– Nucleus:
• variable in shape (polymorphnuclear leukocytes)
• Consist of 2 – 5 lobes connected by chromatin filaments
– Cell membrane:
• contain receptors for Ig G and complement (C3b).
½ the total number of neutrophils are circulating free in the
blood and the other ½ are marginated along the blood vessel
walls.

11. a) Function of neutrophils
- Neutrophils are the first line defense against infection.
- When infection occurs, large number of neutrophils invade the infected area,
then phagocytose & destroy the organism.
Mechanism:
1- Margination: is sticking of the neutrophils to the capillary wall.
2- Diapedesis : the neutrophils squeeze themselves through the capillary
pores .
3- Amaeboid movement : to reach the site of infection .
4- Chemotaxis: the neutrophils are chemically attracted to the site of
infection by a group of substances called chemotactic factors:, they
include :
a) The bacterial toxins.
b) The products of tissue destruction.
c) Components of the complement system (C5a)
d) leukotriens..

13. a) Function of neutrophils
5- Phagocytosis:
- Once the neutrophils reached the site of infection they ingest the bacteria
by endocytosis. Phagocytosis is facilitated by antibodies & C3 component
of the complement.
1) - They adhere to the bacterial membrane, then C3 binds to specific
receptors on the neutrophil membrane initiating phagocytosis, this
process of fascilitation is called opsonization
2) - Then the neutrophils project their pseudopodia to phagocytose the
organism, which forms phagocytic vesicle.
3) - The organism inside the phagocytic vesicle is then killed by:
1) the lysosomal proteolytic enzymes
2) bactricidal agents formed inside the neutrophil as:
• a - oxidizing agents as hydrogen peroxide & hydroxyl ions.
• b- hypochlorite that results from the reaction between H2O2 & chloride.
• - Neutrophils phagocytose up to 20 organism then die.

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15. Eosinophils
Count: 1 – 5 % of TLC
Structure:
– Diameter: 10 – 12 µm
– Cytoplasm:
• contain coarse granules stained red with acidic dye (so called
eosinophils)
– Nucleus:
• Consist of 2 lobes bilobed
– Cell membrane:
• contain receptors for Ig E and Ig G, Ig M and complement

16. b) Functions of eosinophils
1- They are weak phagocytes.
2- Protect the body against parasitic infection e.g schistosomiasis:
• - They migrate to the infected area & kill the juvenile forms of the organism
by:
a- Hydrolytic enzymes.
b- Larvicidal polypeptides called major basic proteins.
c- highly reactive forms of oxygen..
3- Prevent spread of the inflammation resulting from allergic reaction
because they:
a) Phagocytose the antigen- antibody complex.
b) Detoxify the inflammation producing substances released from mast cells
and basophils

17. Basophils
Count: 0.5 – 1 % of TLC
Structure:
– Diameter: 8 – 10 µm
– Cytoplasm: contain coarse granules stained blue with
basic dye (so called basophils)
– Nucleus: segmented of 2 – 3 lobes
– Cell membrane: contain receptors for Ig E
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18. c) Functions of basophils
1- Synthesize & liberate heparin into circulation to prevent blood coagulation.
2- Has a role in allergy:
– the antigen- antibody reaction occurs on their surface (Ig E) leading to
their degranulation & release of:
• histamine,
• bradykinin &
• serotonin,
• slow reacting substance of anaphylaxis and
• a number of lysosomal enzymes
– which are responsible for allergic manifestations.
3) Share in inflammatory reactions: by the released substances

19. II) Function of non-granular leukocytes
a) Function of lymphocytes:
• - The lymphocytes represent the immune system
b) Function of monocytes:
• Monocytes enter the blood (from bone marrow) then circulate for 72
hours.
• Then they enter the tissues, within 8 hours they  in size & develop
lysosomes & becomes tissue macrophages.
• Tissue macrophages phagocytose & kill bacteria by similar mechanisms to
neutrophils but more powerfully as :
– a) They can phagocytose up to 100 bacteria.
– b) They can engulf much large particles as whole RBCs or a parasite
– c) After destroying the particle, macrophage extrude them outside & survive
for many months.

20. Tissue macrophage system
(reticulo-endothelial system)
• RES consists of:
– Monocytes
– Mobile macrophages & Fixed tissue macrophages
– Endothelial cells in BM, spleen & lymph nodes
The tissue macrophages are 2 types :
1) Mobile macrophages:
• - wander through the tissues all the time.
2) Fixed macrophages:
• They are attached to the tissues & remain attached for months or even years.
• May become mobile macrophages when stimulated in response to chemotaxis.
• The tissue macrophages are known by different names in various tissues:
– kupffer cells in the liver
– Alveolar macrophages in the lung
– Microglia cells in the brain
– mesangial cells in the kidney
– Histocytes in the skin
– Reticular cells in lymphoid tissue (LN, BM, spleen)
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21. Functions of tissue macrophage system
1- Phagocytosis of micro-organisms e.g bacteria & viruses & dead tissues and
foreign particles.
2- Engulfing of old blood cells.
3- Breakdown of HB & formation of bile pigment (e.g bilirubin).
4- Repair of damaged tissues after inflammation by engulfing the necrotic
tissues & release tissue growth factors.
5 - Production of 10 % of erythropoietin by von kupffer cells in liver.
6- Help in production of antibodies by B-lympholytes:
– a) Upon entry of the foreign antigen to the body, macrophages phagocytize it
then digest it, then present its antigenic structure to B lymphocyte which
begin to form the antibodies .
– b) macrophage then secrete IL1 that activate T helper lymphocyte which by
its turn activates B lymphocytes to form antibodies.

22. * It represents the difference between the filtered and the reabsorbed
fluids across the capillary membrane.
* Normally, lymph flow rate is: 120 ml./hour (i.e., 2-4 L/day) during
rest.
Lymphatic Circulation
Definition:
Lymph is the fluid that returns to the blood stream from tissue spaces
by lymphatic vessels.
Rate of lymph flow:
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23. Thorathic duct Right lymphatic duct
* drains lymph from:
lower limbs – abdomen – left half of
thorax – left side of head and neck –
left upper limb.
* lymph flow rate: 100 ml./hour.
* drains in the left subclavian.
* drains lymph from:
right half of thorax – right side of head
and neck – right upper limb.
* lymph flow rate: 20 ml./hour.
* drains in the right subclavian.
lymphatic capillaries which unit together large lymphatic vessels (have
unidirectional valves) 2 lymphatic ducts:
Lymph is drained by lymphatic system:
1- Almost all the body have lymphatic drainage except:
Brain - deep parts of nerves – superficial parts of the skin –
bone.
2- Lymphatic system is formed of:

24. Lymph is a part of the interstitial fluid (I.S.F.) characterized by the following:
Physical:
- colourless. – isotonic. - pH 7.4.
- transparent except during fat absorption where It looks milky due to fat globules.
Chemical: It is similar to plasma except in:
* Less proteins (average 2 gm%) but protein concentration varies according to
the site of drainage form 0-6 gm% .
* A/G ratio is greater in lymph than in plasma because albumin has smaller
molecular weight.
* Less number of lymphocytes than plasma.
* Less amount of fibrinogen, prothrombin, Ca++ and no platelets, so it clots but
slower than plasma.
Composition of lymph:

25. 1. Drainage of excess I.S.F. from capillaries back to the blood --> prevent
accumulation of fluid and edema. This also maintains blood volume.
2. Removal of substances having large molecular weight (proteins and
metabolites), because lymphatic capillaries are more permeable than blood
capillaries. The amount of proteins returns to blood by lymph is 25 - 50% of
total circulating plasma proteins, so lymph flow maintains plasma proteins.
3. Absorption of fat and fat - soluble vitamins from the intestine.
4. Lymph nodes functions are:
- formation of lymphocytes.
- removal of bacteria (protective mechanism).
Functions of lymphatic system:

26. Immune
organs

27. Immune defenses can be classified into 2 types which usually
interacts:
Nonspecific immune
defenses
(Innate Immunity)
 Protect against microbes
or F.B. (invaders) without
having to recognize their
specific identity.
 The mechanisms used are
not specific to any invader.
Specific immune
defenses
(Acquired Immunity)
 Protect against microbes to
which the body is previously
exposed (recognized before)
either through infection or
immunization.
 The mechanisms used are
specific for each invader.

28. Acquired ImmunityInnate Immunity
Specific
i.e., Reacts to a specific
invader each time and can
not react to another.
Non-specific
i.e., Reacts to invaders from
different type
Specificity
Very high
i.e., Although the cells are of
the same type, each group
shows totally different
surface molecules.
LimitedDiversity
Yes
Remembers the invader on
re-exposure.
NoMemory
YesYesNon-reaction to self
Components
LymphocytesPhagocytes & natural killer
cells
Cells
AntibodiesComplementMolecules
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29. Mechanisms of Innate Immunity
I - Defenses at Body Surfaces
Very few microorganisms can penetrate the intact skin,
Various skin glands & tears contain anti-microbial agents
Mucus secreted by epithelial lining contain antimicrobial agents and sticky
to which microbes adhere.
Hairs at the entrance of nose
Cough and sneezing reflex
Acid secretion by the stomach and uterus

30. II- Inflammation
1. Initial entry of bacteria into tissue
2. Vasodilation in the infected area, leading to increased blood flow
3. Marked increase in protein permeability of the capillaries and venules in
the infected area, with resulting diffusion of protein and filtration of fluid
into the interstitial fluid.
4. Chemotaxis: exit of leukocytes from the venules into the interstitial fluid
of the infected area
5. Destruction of bacteria in the tissue either through phagocytosis or by
mechanisms not requiring phagocytosis.
6. Tissue repair

31. family of plasma proteins which is involved in:
1) killing of microbes without prior phagocytosis.
2) Opsonization: making phagocytosis easier.
3) Chemotaxis: Direction of phagocytes toward the source of infection.
III- Complement
opsonization

32. IV- Interferons
are a family of cytokines that nonspecifically inhibit viral replication inside host
cells
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33. Antigen (immune stimulant)
Is any foreign substance which when introduced into the body ,is
capable to stimulates specific immune response.
Antigen nature:
either proteins or high molecular weight polysaccharides (8000
or greater) that are specific for each type organism.

34. Basic types of acquired immunity
2) Cell-mediated immunity
= T cell immunity
1) Humoral immunity
= B cell immunity
1. Performed by T-lymphocytes
2. It's a major defense against
viral & fungal infection
3. The T-cell them selves can
kill the abnormal cells.
4. It is also responsible for
allergic reactions and
rejection of transplanted
organs.
1. Performed by B-lymphocytes
2. It's a major defense against
bacterial infection
3. The B-lymphocytes produce
antibodies that kill bacteria

35. Acquired Immunity involves the following steps:
1) Antigen recognition and presentation by “antigen presenting
cells”.
2) Lymphocyte activation and differentiation.
3) Elimination of antigen by:
a) Antibodies secreted by plasma cells (differentiated from B-
lymphocytes).
b) Direct attack by activated T-cytotoxic cells.

37. Functions of different types of T-lymphocytes
1) Helper T-lymphocytes (TH cells):
- They are the most numerous of the T-cells (75%).
- They serve as the major regulator of all immune functions. They do this by
forming a series of protein mediators, called lymphokines, that act on other cells
of the immune system as well as on the bone marrow cells.
2) Cytotoxic-T cells (Tc) or killer cells
-Tc is a direct attack cell that is capable of killing micro-organisms and some of
the body’s own cells specially when they are cancerous or invaded with viruses.
They are also responsible for rejection of transplants of foreign tissues.
3) Suppressor T-lymphocytes (Ts cells)
-Ts cells are capable of suppressing the functions of both cytotoxic and helper T
cells.

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