Hematopoietic stem cells in the bone marrow can differentiate into various blood cell types, including red blood cells, neutrophils, eosinophils, basophils, mast cells, monocytes/macrophages, dendritic cells, B lymphocytes, T lymphocytes, and natural killer cells. These cells play important roles in immunity, such as phagocytosis of pathogens by neutrophils and macrophages, antibody production by B cells, and cytotoxic killing by natural killer and T cells.

1. CELLS OF IMMUNE SYSTEM
Nidhi Saxena
Department of
Microbiology

2. INTRODUCTION
All blood cells arise from a type of cell called the hematopoietic stem cell
(HSC).
Stem cells are cells that can differentiate into other cell types; they are self-
renewing—they maintain their population level by cell division.
Hematopoiesis is the formation and development of red and white blood
cells.
In human, it starts in the embryonic yolk sac during the first weeks of
development.
In the third month of gestation, hematopoietic stem cells migrate to the fetal
liver and then to the spleen.
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3. After birth, HSCs move to the bone marrow and differentiate to form
blood cells.
Hematopoietic stem cell is multipotent, or pluripotent, able to self-
renewal, can differentiate into erythrocytes, granulocytes, monocytes,
mast cells, lymphocytes, and megakaryocytes.
These stem cells are few (approx one HSC per 5 x 104 cells) in the bone
marrow.
INTRODUCTION
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4. Hematopoiesis is regulated at the genetic level
Factor Dependent lineage
GATA-1 Erythroid
GATA-2 Erythroid, myeloid, lymphoid lineages development
PU.1 Erythroid (maturational stages), myeloid (later stages),
lymphoid
Bmi-1 Self renewal capacity of HSC
Ikaros Lymphoid development.
Oct-2 B lymphoid (differentiation of B cells into plasma
cells)
Notch1 Regulates the choice between T and B lymphocyte
lineages
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6. CELLS OF IMMUNE SYSTEM
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7. Neutrophils are circulate 7-10 h in peripheral blood then migrate into the
tissues, where they live only a few days.
These cells generally are the first to arrive at a site of inflammation.
Some chemotactic factors (complement components, cytokines etc.)
promote accumulation of neutrophils at inflammatory site.
Phagocytosis by neutrophils is done by lytic enzymes and bactericidal
substances contained within primary and secondary granules.
Neutrophils express higher levels of defensins than macrophages.
NEUTROPHIL
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8. EOSINOPHILS
Eosinophils are motile phagocytic cells that can migrate from
the blood into the tissue spaces.
The secreted contents of eosinophilic granules may damage the
parasite membrane.
They play role in the defense against multicellular parasitic
organisms e.g. worms.
Eosinophils secrete cytokines that regulate B and T lymphocytes
and influencing the adaptive immune response.
Eosinophils are also contributors to asthma and allergy symptoms.
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9. BASOPHIL
Basophils are nonphagocytic granulocytes that contain large granules
filled with basophilic proteins.
Basophils response against parasites, and cause allergy symptoms.
Basophils secrete cytokines that modulate the adaptive immune
response.
Basophils are function by releasing pharmacologically active
substances from their cytoplasmic granules. These substances play a
major role in certain allergic responses.
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10. MAST CELLS
Mast cells are found in a various tissues, Example skin, connective
tissues of various organs, and mucosal epithelial tissue of the
respiratory, genitourinary, and digestive tracts.
Mast cells activated by microbial products binding to Toll Like
Receptors (TLRs).
Mast cell granules contain vasoactive amines such as histamine cause
vasodilation and increased capillary permeability and proteolytic
enzymes that can kill bacteria or inactivate microbial toxins.
Mast cells also synthesize and secrete lipid mediators and cytokines,
which stimulate inflammation.
Mast cells, with blood basophils causes the development of allergies.
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12. It consists monocytes circulating in the blood and macrophages in the
tissues.
Promonocytes, leave the bone marrow and enter the blood, where they
differentiate into mature monocytes.
Monocytes circulate in the bloodstream for about 8 h, during which they
enlarge; then migrate into the tissues and differentiate into tissue specific
macrophages such as Intestinal macrophages found in the gut, Alveolar
macrophages found in the lung, Histiocytes found in connective tissues,
Kupffer cells found in the liver, Mesangial cells found in the kidney,
Microglial cells found in the brain and Osteoclasts found in bone.
MONONUCLEAR PHAGOCYTES
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13. Differentiation of monocyte
into macrophage:
• Cell enlarges 5 to 10 folds
• Intracellular organelles
increase in number and
complexity
• Increased phagocytic
ability
• Produces higher levels of
hydrolytic enzymes
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14. Phagocytosis
Macrophages are capable of ingesting
and digesting exogenous antigens
(whole microorganisms and insoluble
particles) and endogenous matter
(injured or dead host cells, cellular
debris, and activated clotting factors).
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15. Dendritic cells (DC), first cells of the immune system to be discovered, acquired
its name because it is covered with long membrane extensions that resemble the
dendrites of nerve cells.
Immature dendritic cells capture antigens and then migrate to lymph nodes
where they present the antigen to T cells.
They take cargo in 3 ways: phagocytosis, internalize by receptor mediated
endocytosis or imbibe by pinocytosis.
Langerhans DCs (epidermis), Interstitial DCs (interstitial spaces), Monocyte-
derived DCs (arise from monocytes).
They all display class I and II MHC, CD80, CD86 and CD40 which required to
interacts with T cells.
DENDRITIC CELLS
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17. Follicular Dendritic Cells
• Do not arise in bone marrow.
• Do not express MHC Class II molecule and hence do not function as
antigen presenting cell.
• Present in lymph follicles (lymph nodes).
• High level of membrane receptors for antibody.
• Interaction of B cells with follicular dendritic cells is an important step
in the maturation and diversification of B cells.
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18. B lymphocytes
They mature within the bone marrow and expresses antigen-binding
receptor (1.5 x 105 molecules of antibody).
When a naive B cell first encounters the antigen that matches its
membrane bound antibody, causes the cell to divide rapidly; its progeny
differentiate into memory B cells and effector B cells.
Memory B cells have a longer life span than naive cells, and they
express the same membrane-bound antibody as their parent B cell.
Plasma cells produce the antibody in secretary form (2000 molecules of
antibody per second) and live for only a few days.
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20. T lymphocytes
Arise in the bone marrow and migrate to the thymus gland to mature
express a T-cell receptor on its membrane.
T-cell receptors can recognize antigen that is bound to major
histocompatibility complex (MHC) molecules.
Naive T cell encounters antigen with a MHC molecule, proliferates and
differentiates into T helper (display CD4) and T cytotoxic (display
CD8) cells.
The ratio of TH to TC cells is approximately 2:1 in normal human.
TH cells secrete various cytokines, which play a central role in the
activation of B cells, Tc cells, macrophages, and other cells.
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22. Natural Killer Cells
Large, granular lymphocytes, show cytotoxic activity against a wide
range of tumor cells and against cells infected with some viruses.
NK cells recognize target such as tumor cells and cells infected by
certain viruses display antigens bound by antitumor or antiviral
antibodies.
NK cells express CD16, a membrane receptor for the carboxyl-
terminal end of the IgG molecule, can attach to these antibodies and
subsequently destroy the targeted cells, process known as antibody-
dependent cell mediated cytotoxicity (ADCC).
NKT cell have T cell receptors, Interact with CD1 instead of MHC class
I or II molecules.
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25. REFERENCES
1. Kuby, J., Goldsby, R. A, Kindt T. J., Osborne B. A. (2013). Immunology 7th
edition, W.H. Freeman and Company, New York.
2. Lyolyard, P. M., Whelan, A., Fanger. M. (2011) Instant Notes in Immunology.
3rd edition. Garland Science Taylor and Francis Group, Newyork
3. A. K. Abbas, A. H. H.Lichtman, S. Pillai. (2017).Molecular and Cellular
Immunity. 9th edition. Elsevier
4. C. A. Janeway, P. Travers, M. Walport, M. J. Shlomchick. (2005). Immunology –
the immune system in health and Diseases. 6th edition. Garland Science
Taylor and Francis Group, Newyork
5. K. Murphy, P. Travers, M. Walport. (2008). Janeway’s Immunology. 7th edition.
Garland Science Taylor and Francis Group, Newyork
6. J. M.Cruse, R. E. Lewis. (2009). Illustrated Dictionary of Immunology. 3rd
edition. CRC Press Taylor and Francis Group, New York.
7. Google
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