The document summarizes the cells of the immune system. It discusses how hematopoietic stem cells differentiate into either myeloid or lymphoid progenitor cells through hematopoiesis. The myeloid lineage gives rise to red blood cells, platelets, neutrophils, basophils, eosinophils and monocytes/macrophages. The lymphoid lineage produces B cells, T cells and natural killer cells. Each cell type is described in terms of its identifying markers, functions, and role in the immune response. The document also discusses cytokines that mediate communication between immune cells.

1. Cells of the Immune System
Hawler Medical University
College of Health Sciences
Medical Microbiology Dept.
Dr. Amer Ali Khaleel
Medical Immunology
Lecture 2
2nd stage
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2. Introduction:
• The cells of the immune system arise from a pluripotent
Hematopoietic Stem Cells (HSCs) through a process known as
haematopoiesis.
• Hematopoiesis involves the production, development, differentiation,
and maturation of the blood cells (erythrocytes, megakaryocytes and
leukocytes) from HSCs.
• Differentiation of the HSC will occur along one of two pathways,
giving rise to either a common myeloid progenitor or a common
lymphoid progenitor cells in the presence of specific cytokines or
soluble mediates (growth factor).
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3. Introduction:
• The HSCs are self-renewing cells, when they proliferate at least some
of their daughter cells remains as HSCs.
• The site of hematopoiesis changes during development. During
embryogenesis and early fetal development, the yolk sac is the site of
haematopoiesis. Once organogenesis begins, hematopoiesis shifts to
the liver and spleen, and finally, to the bone marrow where it will
remain throughout adulthood.
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5. Cytokine:
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 Cytokines are signaling proteins that help cells communicate with each other,
initiating and coordinating immune actions. Most cells in our body are capable of
making and releasing at least one type of cytokine. Hundreds have been identified,
and many more are still to be characterized. Cytokines are often grouped by
functions. For example, cytokines that induce inflammation are collectively called
pro-inflammatory cytokines.
 Cytokines have become central in clinical medicine as diagnostic, prognostic, and
even therapeutic agents. Due to their increasing role in clinical applications, it is
useful for allied health students to have a basic understanding of these molecules.

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1. Interleukin (IL)
2. Tumor Necrosis Factor (TNF)
3. Interferon (IFN)
4. Colony stimulating factor (CSF)
5. Transforming growth factor (TGF)
6. Chemokines
Cytokine Type:

7. • Immune responses are mediated by specific cells with defined
functions.
• For each of the cells know CARP:
• Cell-surface markers (e.g., CD4, TCR, etc.),
• Actions (kill, suppress, activate, etc.),
• Role (type of response), and
• Products (cytokines, antibody, etc.).
Cells of the Immune Response:
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8. • Neutrophils.
• Basophils ( Mast cells ).
• Eosinophils.
• Monocytes (macrophage precursors ).
• Dendritic cells (DC).
• Platelets.
• Erythrocytes (RBCs).
1-The common myeloid progenitor cells give rise
the following cells: -
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9. which is include monocyte (bloodstream).
Features:
• It is agranulocyte.
• Mononuclear cells give rise to monocyte (Circulate in the
bloodstream), which develop into macrophage Mφ (Resident in all
tissues) after migrating into tissue.
• Percentage in blood: 1-6% of total WBC. (per microliter)
• Presence of foreign surface antigens: Yes
• Presence of surface antibodies: No
• Life span: Long 9
A-Mononuclear Cells:

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Macrophage Location Name
Liver Kupffer cells
Kidney Mesangial phagocytes
Central nervous system Microglia
Connective tissues Histiocytes
Bone Osteoclasts
Lung Alveolar macrophages (dust cell).
Joints
Synovial A cells
Spleen, lymph node and thymus
sinusoidal lining macrophage
Abdominal cavity (peritoneum).
Peritonial macrophage
• In the tissues, mononuclear phagocytes, they differentiate into different
histological forms for example:
• They are particularly abundant in liver, spleen, lymph nodes, lungs, and the
peritoneal (abdominal) cavity.

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12. Functions of macrophage:
1. Phagocytosis (big eater).
2. Professional antigen presenting cell (APCs).
3. Production of cytokines, such as IL-1, IL-6 and TNF, which are
proinflammatory ,in order to signal and recruit other cells to an area with
pathogens.
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IL=Interleukin
TNF= Tumor necrosis factor

13. • Dendritic cells are found in
various tissues throughout the
body, where they function as
“scouts.”
• They routinely engulf material in
the tissues, and then bring it to the
cells of the adaptive immune
system for “inspection.”
• Dendritic cells develop from
monocytes, but some also appear
to descend from other cell types.
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14. B-Multinuclear Cells:
They are consisting of neutrophilic, eosinophilic and basophilic cells.
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15. Neutrophils:
Features:
* Circulate in the blood.
* Percentage in blood: 60-70% of total WBC.
* Highly mobile (very active).
* Short lived.
Functions:
1-Strongly phagocytes cells (eater) at killing extracellular pathogens.
2-It plays important role in inflammatory response.
3-They are first cell (respond quickly) arrive to the infection /injury site & ingest
and destroy microbes.
4-Granules contain myeloperoxidases (MPO), able to create cytotoxic substances
capable of killing bacteria and other engulfed pathogens.
5-Cytokine production. 15

16. Eosinophils:
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Features:
* Percentage in blood: 1-3% total WBC.
* It is present in large numbers during worm infections.
Functions:
1-Weakly phagocytic cells.
2- Their major function is to produce toxic proteins against certain parasites, such as
helminths. Although eosinophils are physically too small to ingest and destroy
helminths, they can attach to the outer surface of the parasites and discharge peroxide
ions that destroy them.

17. Eosinophils:
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18. Basophils (Circulate in the bloodstream):
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Features:
* Non-Phagocytes.
* Percentage in blood: Basophils comprise <1% of circulating WBCs.
* Whereas mast cells are resident in the most tissues adjacent (alongside)
to blood vessels.
* Location: mast cell found in skin, connective tissues & mucosal
epithelial tissue has large numbers of cytoplasmic granules that contain
histamine, and heparin.
* They have cell surface receptors (Fc) specific for immunoglobulin IgE.

19. Functions:
1. Basophils are responsible for the body's allergic response.
2. Basophils are granulocytes whose granules contain substances such
as histamine and heparin. Heparin thins blood and inhibits blood clot
formation. Histamine dilates blood vessels and increases blood flow,
which helps the flow of white blood cells to infected areas.
3. They produce a variety of cytokines.
Also, platelets and RBCs (Non-leukocytes) are produce from common
myeloid progenitor cells.
Basophils:
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20. Which are includes B Lymphocytes, T Lymphocytes and NK cells.
* Lymphocyte: 20-35 %.
* Participate in innate (NK cell) and adaptive (B & T) immune responses.
* Found in lymphoid organs (such as lymph nodes, spleen, thymus,
appendix, tonsils), also in circulation.
* In fact, the proliferation of lymphocytes is one factor responsible for the
swelling of lymph nodes during an infection.
2-The common lymphoid progenitor cell gives rise the
following cells:
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Which includes B & T cell.
1-B lymphocyte (B cell), also sub-classified into subsets
• Plasma cell.
• Memory B-cell.
• Regulated B-Cell.
A-Small agranular lymphocyte:

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2- T lymphocyte (T cell), also sub-classified into subsets:
* T Helper cell (CD4).
* T Cytotoxic cell. (CD8)
* Regulatory T-cells (Treg) previously called T Suppressor (Ts cell).
* Memory T-cell

23. Which is include NK cell.
Features:
• Natural killer cells (often simply called NK cells).
• Circulate in the bloodstream.
• 5 -10% peripheral blood lymphocytes.
• NK cells express (surface markers, receptors) CD16, CD56.
• Lymphocyte member of innate immune system.
• Activity not enhanced by prior exposure.
• Have no memory.
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B-Large granular lymphocyte:

24. Functions:
1. Immune surveillance (like security or scanner).
2. They play a role in organ transplantation, recognize virus-infected
cells by detecting lack of class I MHC proteins on the surface of
the infected cells.
3. Kill virus-infected cells and cancer cells using perforin and
granzyme.
4. Produce gamma interferon that activates macrophages to kill
ingested bacteria.
Natural killer cells (NK cells)
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Killing strategy:
The binding of NK cells to a target cell, such as an infected human cell,
causes the release of vesicles containing toxic substances from NK cells.
Some granules contain a protein called perforin, which inserts into the
plasma membrane of the target cell and creates channels (perforations) in
the membrane. As a result, extracellular fluid flows into the target cell
and the cell bursts, a process called cytolysis.
Other granules of NK cells release granzymes, which are protein-
digesting enzymes that induce the target cell to undergo apoptosis, or
self-destruction. This type of attack kills infected cells but not the
microbes inside the cells; the released microbes, which may or may not
be intact, can be destroyed by phagocytes.

26. Figure : The action of natural killer (NK) cell.
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27. Prevalence of Leukocytes
• The relative proportions of the different types of white blood cells are:
• Neutrophils (roughly 60 – 70%)
• Lymphocytes (roughly 20 – 30%)
• Monocytes (approximately 1 – 6%)
• Eosinophils (approximately 1 – 3%)
• Basophils (less than 1%)
Mnemonic: Never Let Monkeys Eat Bananas
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precursor

29. Next Lecture
Organs of the Immune system
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