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Leukocytes: The Granulocytic and
Monocytic Series
Part I
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Learning objectives:
Upon completion of this lecture series the learner should
be able to competently discuss:
The differentiation and maturation of the granulocyte cell
series in detail
The differentiation and maturation of the monocyte-
macrophage cell series in detail
The function of granulocytes and monocytes
Methods of assessment of granulocytes and monocytes in
a clinical setting (absolute counts, differential counts,
morphology, staining patterns, etc.)
Chapter 14
The Leukocytes
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Part I: Granulocytes
Development and proliferation passes through 3 major phases in 3
different sites:
Phases
1. Proliferative phase:for cell number to increase and for
cells to start to differentiate
2. Maturation-storingphase: cells complete their maturation
and replenish the constantly changing reservoir in the BMstorage compartment.
3. Distribution / release to circulationthen to final
destination depending on demand which changes; infection
and tissue injury increases demand.
Sites
- Proliferative compartment of BM
- Maturation/storing compartment of BM
- Circulation & the endothelium of the vascular system)
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Journey of a leukocyte
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Proliferative phase
Occurs in the proliferative compartment (mitotic pool) of BM which
houses cells capable of DNA synthesis & mitosis 4 stages:
Myeloblast: blastdenotes enlarged cells undergoing proliferation; representthe first cell that is morphologically recognizable as a granulocyte (granulation,
N/C ratio, chromatin pattern [clumped vs. dispersed], shape of nucleus, etc.)
Promyelocyte
Myelocyte
Metamyelocyte
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Maturation-storing phase:
Within this compartment metamyelocytes coming from
proliferative compartment make up to 45% of cells
Mature into band neutrophils (35%) [band describes the shape
of the nucleus in such cells
Further develops into segmented neutrophils (20%)
[segmented pertains to shape of nucleus as well].
Note that same phases apply to basophils, eosinophils and
monocyets.
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Band vs. segmented neutrophil
Band neutrophil in
peripheral blood film
Segmented neutrophil in
peripheral blood film
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Distribution / Release to circulation:
Under the influence of various profiles of interleukins&
concurrent with the expression of homing markers(various
members of the selectin and integrin families like VCAM, ICAM, L-
selectin, LFA-1, etc) on vascular endothelium, mature
granulocytes start rolling towards sinusoid walls of BM into
circulation.
Granulocyte movement is also enhanced by cellular changes
decrease in size, N/C decrease, increased flexibility.
In the vascular system cells either stay in circulationor gather at
marginatingpools.
Marginating granulocytes adhere to the endothelim of blood
vessels; can be released on demand.
If needed as phagocytes (e.g. tissue injury), granulocytes (mainly
neutrophils) exit circulation to tissues by diapedesis.See next slide
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Developmental pathways of granulocytes & monocytes
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Maturation of Neutrophils1. Myeloblast
Earliest neutrophil precursor
Size: 10-18 mN:C ratio: High(4:1)
Nucleus: Oval or round
Chromatin: delicate, lacy, evenly stained
Nucleoli: 3-5
Cytoplasm: small rim of basophilic cytoplasmthat lacks granules.
Golgi apparatus: unstained area adjacent tonucleus
CD markers: CD33 and CD38.
Auer rods : which are aggregates of fused
lysosomes, may appear as red, needle-like
crystalline cytoplasmic inclusions.
These inclusions may appear alone or in
groups
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Maturation of Neutrophils
2. Promyelocyte
Size: larger than blast (14-20 m)
N:C ratio: High(3:1)
Nucleus: large, Oval or round
Chromatin: Coarser than blasts, lacy, purple-blue
Nucleoli: less prominent or absent
Cytoplasm: pale grayish blue.
Granules: Large blue purple primary granules (azurophilic
granules that contain loads of AMPs = antimicrobial
peptides(myeloperoxidase and chloroacetate esterase.
M t ti f N t hil
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Maturation of Neutrophils
3. Myelocyte
(The last stage that is capable
of division within BM)
Size: 12 to 18 m
N:C ratio: Decreased(2:1-1:1)
Nucleus: has a more oval appearance thanin previous stages
Chromatin: More condensed than blasts
Nucleoli: Usually absent
Cytoplasm: Light pink, with blue batches
Granules: Secondarygranules (specific): small, pink red to
pink violet in color.
The separate cell types: neutrophils, eosinophils, and
basophilsbecome visibly recognizable at this stage.
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Maturation of Neutrophils
4. MetamyelocyteSize: 10 to 18 m
N:C ratio: Decreased
Nucleus: Kidney-bean shaped
Chromatin: coarse, clumped, stains dark purple
Nucleoli: Not visible
Cytoplasm: Neutral pink
Granules: Predominance of
small pinkish red specific granules
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Maturation of Neutrophils
5. Band Neutrophil
(also called stab neutrophil,
and may normally present
in peripheral blood).
Size: 10 to 16 m
N:C ratio: Decreased (1:1)
Nucleus: More indented than
metamyelocyte
Horseshoe shape
Chromatin: pyknotic (condensed) at either end
of nucleus, Stain dark purple
Cytoplasm: Pink
Granules:Abundant small pinkish red specific granules
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Maturation of Neutrophils
6. Segmented Neutrophil
(Polymorphonuclear)Size: 10 to 16 m
N:C ratio: Decreased
Nucleus: Segmented, with
two to five lobes connected
by thin filament
Chromatin: condensed, stain deep
purple blackCytoplasm: Pink
Granules: Mainly small pinkish red
specific granules
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Maturation of Eosinophils
Morphological maturation of eosinophils is similar
to that of neutrophils.
Only at the myelocyte stage can the cell be
identified as an immature eosinophil.
Eosinophilic myelocyte contain large, eosin-
staining granules.
Maturation from myelocyte to the metamyelocyte,
band, and segmented eosinophil stage is similarto
neutrophils.
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Characteristics of Eosinophils
Size: 12 to 15 m
Nucleus: No more than 2-3
lobes.
Chromatin: Stain dark purple
Cytoplasm: Orange red
Granules:Abundant with large
acidophilic (Eosin-loving) granules.
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Maturation of Basophils
Morphological maturation of basophils is similar
to that described for neutrophils.
First recognizable stage is promyelocyte:
basophilic promyelocyte is smaller, with higher
N:C ratio than that of neutrophil or eosinophil
Basophilic promyelocyte contain large purple
black granules.
Maturation from promyelocyte to the
metamyelocyte, band, and segmented basophile
stage is similarto neutrophils.
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Basophilic granules contain
heparin and histamine.
Mast cells have granules that
have an enzyme content
similar to those of the blood
basophil.
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Size: 10 to 15 mNucleus: Segmented
Chromatin: Stain dark
purple
Granules: Many purple
in color, obscuring
the background of
the cytoplasm
Characteristics of Basophils
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Myeloblast: High N/C ratio. Cytoplasm is agranular. Nucleus has a fine
chromatin pattern
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Promyelocyte: Cytoplasm contains nucleus with a fine chromatin pattern and
nucleoli. Numerous primary azurophilic granules.
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Myelocyte: Cytoplasm is pinkish blue, indicating secondary granuleformation.
Nucleus is oval and eccentric with a moderately clumped chromatin pattern.
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Metamyelocyte: Cytoplasm contains a few azurophilic primary granules but
mostly pinkish-blue secondary granules. Nucleus indented with dense chromatin
clumping.
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Neutrophilic Band: Cytoplasm is pinkish-blue due to secondary granules. Nucleus is
clumped, and has a horseshoe shape that has uniform width throughout the nucleus.
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Segmented Neutrophil: Cytoplasm is finely granulated. Nucleus is segmented.
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Eosinophilic Myelocyte: Cytoplasm contains numerous red-orange granules and few
dark azurophilic granules. Nucleus is oval and eccentric.
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Basophilic Myelocyte: Cytoplasm has smaller black granules that are more intense on
the right of the nucleus. Nucleus is oval with moderately clumped chromatin.
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Basophil:Cytoplasm contains numerouslarge black granules thatobscure the nucleus.
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