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Immunology Lecture 3rd
Cells of Immune System
BY
Dr. Humera Kausar
March 2015
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Cells of the Immune System
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ImmuneCells
Myeloidcells
Granulocytic
Neutrophils
Basophils
Eosinophils
Monocytic
Macrophages
Kupffer cells
Dendritic cells
Lymphoidcells
T cells
Helper cells
Suppressor cells
Cytotoxic cells
B cells
Plasmacells
NK cells
Cells of the Immune System
Leucocytes
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Cells of the innate immune system:
• Phagocytes
– Monocytes/macrophages
–
Neutrophils/PMNs/• NK cells
• Basophils and mast cells
• Eosinophils
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Phagocytic Cells MononuclearPROMONOCYTES
MONOCYTES MACROPHAGES (Fixed or Free)
Brain ---------Microglial cells
Lungs ------------Alveolar cells
Liver ----------------- Kupffer cells
Connective tisues-----HistocytesKidney ---------------------Mesangial cells
Bones ------------------------ Osteoclasts
Skin ------------------------Langerhans cells
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Macrophages
• Characteristic nucleus
• lysosomes
• CD14 membranemarker protein
Macrophage
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Macrophages
Activated by variety of stimuli in the course of an
immune response. Activated macrophages are more effective then
resting ones in eliminating potential pathogen.
Activated macrophages secreted various cytotoxicproteins that help to eliminate broad range of targets
including
o virus infected cells
o Tumor cells
o Intracellular bacteria
Also act as antigen presenting cells
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Macrophage as an antigen presenting cells
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Granulocytes
Neutrophils
Polymorphonuclear (PMN) leukocyte.
Has multilobed nucleus and granulated cytoplasm.
Stains with both acidic and basic dyes.
Constitute 50% to 70% of the circulating
leukocytes.
After release in to the blood, circulates 7 – 10 hours
before migrating in to the tissues.
Life span is few days. (3 days)
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Neutrophils (PMNs)
•
CD66 membranemarker protein
Geimsa stains
Neutrophil
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Neutrophils
First cells to arrive at the site of inflammation.
In response to many types of infections the bonemarrow releases increased number of circulating
neutrophils called leukocytosis.
Act as phagocytic cells.
GRANULOCYTES
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Neutrophils GRANULOCYTES
Lytic enzymes and bactericidal substances in
neutrophils are contained within primary andsecondary granules.
Larger denser primary granules are a type of
lysosome containingperoxidase, lysozyme, various hydrolytic enzymes
Smaller secondary granules contains,
collagenases, lactoferr in, lysozyme
Both primary and secondary granules fuse with
phagosomes.
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Neutrophil
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Eosinophils
Stain with acid dye eosin red.
Has bilobed nucleus and granulated cytoplasm.
Constitute 1% to 3% of WBC population.
Like neutrophils, motile phagocytic cells that can
migrate from blood into tissues.
Phagocytic role of eosinophils are less significant
than that of neutrophils.
Play a role in the defense against parasitic
organisms by secreting contents of eosinophilic
granules, which damage the parasite membrane.
GRANULOCYTES
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Eosinophil
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Basophils Basophil has a lobed nucleus and heavily granulated
cytoplasm.
Stains with basic dye methylene blue.
Non phagosytic granulocyte.
Constitute <1% of circulating WBC.
Function by releasing pharmacological active
substances from cytoplasmic granules.
Play a major role in certain allergic responses.
GRANULOCYTES
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Basophil
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Mast Cells
By hematopoiesis, released into the blood as
undifferentiated cells.
Do not differentiate until they leave the blood and
enter the tissues, including
skin, connecting tissue of var ious organs,mucosal epithel ial tissues of respiratory,
genitour inary & digestive tracts
Like circulating basophils, mast cells have large
numbers of cytoplasmic granules that contains
histamines and other pharmacological active
substances.
Play an important role in the development of allergies.
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MEDIATORS RELEASED
Prostaglandin D2 Platelet Activating Factor
Tryptase
Heparin Histamin
IL-4, IL-5, IL-6, IL-8
TNF
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CAUSING Vasodilation,
increased vasopermeability,
contraction of smooth muscles, bronchoconstriction,
increased eosinophil, neutrophil & monocyte
chemotaxis,
anticoagulation,
increased fibroblast proliferation,
platelet activation
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Dendritic Cells
Activation of T cells and
initiate adaptive immunity
Found mainly in lymphoidtissue
Function as antigen
presenting cells (APC)
Most potent stimulator of
T-cell response
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Dendritic Cells
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Dendritic Cells
DC covered with long membranous extensions
that resemble the dendrites of nerve cells.
Display class I & class II MHC.
B and T lymphocytes are the mediators ofimmunity, but their function is under the
control of dendritic cells.
Dendritic cells in the periphery capture and
process antigens.
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Dendritic Cells
Express lymphocyte co-stimulatory molecules,
(B7, CD40)
Migrate to lymphoid organs and secrete
cytokines to initiate immune responses. They not only activate lymphocytes, they also
tolerize T cells to antigens that are innate to the
body (self-antigens), thereby minimizingautoimmune reactions.
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Dendritic cells initiate antigen-
specific immune responses
• most efficient of all APCs
• high MHC class I, II & costimulators
•
efficient cross presentation• stimulate naïve T cells (CD4, CD8)
initiate Ag-specific immune responses
All immunization strategies must target DCs
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Immature:
antigen
capture
Mature:
antigen
presentation
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Cells of the immune system:
APC• Cells that link the innate and adaptive arms
– Antigen presenting cells (APCs)
• Heterogenous population with role in innate immunityand activation of Th cells
• Rich in MHC class II molecules
– Examples
• Dendritic cells
• Macrophages
• B cells
• Others (Mast cells)
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Cells of Adaptive Immune
System
T cells and B cells
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Cells of the Adaptive Immune System:
• Lymphocytes (Lymphoid Cells)
– B cells
• Plasma cells (Ab producing)
• Memory cells
– T cells
• Cytotoxic (CTL)
• Helper (Th)
– Th1
– Th2
– Null cells (NK cells)
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Lymphoid Cells
Contributes 20-40% of body’s WBCs, Naïve or unprimed cells are small, motile, non-
phagocytic cells.
Can not be distinguished morphologically. Resting cells are in G0 phase of cell cycle.
Small lymphocytes are 6 um in diameter.
Cytoplasm barely covers the rim aroundnucleus.
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Lymphoid Cells
Have,
o densely packed chromatin
o
few mitochondriao poorly developed endoplasmic reticulum
o Golgi apparatus
Life span of effector cell is few days to few
weeks.
B L h
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B-Lymphocytes
Derived its name from its site of maturation in the
Bursa of fabricius in birds and Bone marrow in humans
• Plasma cells (Ab producing)
• Memory cells
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B-CELL RRECEPTORS
Membrane bond Ig molecules
i.e.,1.5 x 105 molecules/cell
CD 45 (Marker B220) MHC II (Antigen Presenting
receptor)
CD35 (Complement receptor) CD21 (Complement receptor)
CD32 (Fc RII)
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T-CELL RRECEPTORS
TCR
Thy 1 (1st receptor remainsthroughout life span of the cell)
CD4 (T- helper cell)
CD8 (T- cytotoxic cell)
Ratio of Th : Tc = 2:1
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Specificity of adaptive immune
response
• Resides with Ag
Receptor on T and B
cells
•TCR and BCR
– both
specific for only ONE
antigenic determinant
• TCR is monovalent
• BCR is divalent
T cellTCR Ag
B cellBCR
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T-Lymphocytes
T- helper cell vs T cytotoxic cell)
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T helper cells and (TH) Class II MHC proteins
Specialized TH cell involved in
the inflammatory response
Cell-cell interaction mediated
by the TCR and the class II
MHC-antigen complex activates
The TH cell which produces
cytokinesTNF-alpha (tumor necrosis factor)
IFN-gamma (interferon)
GM-CSF (granulocyte-monocyte
colony stimulating factor)
These cytokines further stimulate
macrophages to increase phagocytic
activity and to in turn produce cytokines
that promote inflammation
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Cytotoxic T cells (Tc) and Class I MHC proteins
The cell-cell interaction betweenthe infected cell and the Tc
cell is mediated by the
MHC/antigen complex and TCR
The Tc cell produces cytotoxic proteins
perforins — produce holes or pores in the
target cell and granzymes enter the
virus infected cell causing apoptosis or
programmed cell death
The cytotoxic proteins only affect those
cells to which the Tc cell has specifically
interacted
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NATURAL-KILLER CELLS
A A C S
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NATURAL-KILLER CELLS
Fails to express membrane molecules that
distinguished B and T cells.
Fails to express antigen binding receptors.
Constitute 5% - 10% of lymphocytes in humanperipheral blood.
NK cells have ability to recognize tumor or
virus infected cells.
NK cells express membrane receptor CD16 for
a specific region of antibody molecule (ADCC).
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Human red blood cells
(red), activated platelets
(purple) and white blood
cells - monocyte (green)
and T lymphocyte
(orange).
Colorized-SEM
(scanning electron
micrograph)
Magnification:-1200x--(Based on an image
size of 1 inch in the
narrow dimension)
Cells of the Immune System
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