Production of Specific Cell lineages
2. Leucocyte Production (Leucopoiesis)
Objectives
After completion of lesson, you will be able to
 Describe the pathways and progenitor cells involved in the
derivation of leucocytes from HSC to mature cells
 Name the five stages of maturation of granulocytes and describe
their morphologies
 Discuss functions of granulocytes
 Describe morphology of monocytic and lymphocytic series and
discuss the process of their production
Leucopoiesis
Leucopoiesis
Leucopoiesis
 Granulopoiesis takes 10 to 13 days but mature neutrophil remain 1014hrs in circulation before entering to tissue, soon dies
 There are 3 pools of development of neutrophil: Stem cell,
proliferation, maturation
CMP: CFU-GEMMs; GMP: CFU-GMP and not distinguished from myeloblasts with
light microscope
Source: Rodak’s hematology; 5th edition page 151
Leucopoiesis
• Myeloblast is the earliest recognizable
precursor
• Gives rise to promyelocyte, early
myelocytes, late myelocytes, and then
metamyelocytes
• Promyelocyte contain
• Abundant dark “azurophilic (primary)
granules: overlie nucleus and cytoplasm
Myeloblast
Promyelocyte
Myelocyte (B,N,E)
Metamyelocyte (B,N,E)
• Primary granules become progressively
diluted by the secondary, less conspicuous
“neutrophilic” granules that are
characteristic of the mature cells.
Band (B,N,E)
Segmented (B,N,E)
Myeloblast
Size and shape
• 14 – 20 m in diameter
• Round or oval in shape
 Nucleus: Large, round or oval and eccentric
• Abundant, unclumped, light purple reticulated chromatin
• 2 – 5 light blue-gray nucleoli
• Auer rods present
 Cytoplasm: Stains basophilic (bluish)
• Shows a small indistinct, paranuclear, lighter staining
halo (golgi apparatus)
 Type I: have no visible granules: high N:C: 8:1 to 4:1
 Type II: contains up to 20 visible primary (azurophilic) granules
 Constitute ~1- 3% of the total nucleated BM cells
Myeloblast…
• Auer rods are clumps of azurophilic granular material that form elongated needles
seen in the cytoplasm
• Mostly seen in malignant cells of the neutrophil lineage
Promyelocyte
 Size and Shape: relatively larger than myeloblast
• 16- 25m in diameter and round or oval in shape.
 Nucleus: Similar to myeloblast nucleus
• Round or oval eccentrically located , surrounded by a thin membrane
• A Golgi zone may be visible as a paranuclear halo or hof or clearing.
• The nuclear chromatin is finely dispersed, and nucleoli may be visible.
• Nucleoli (1-3) begin to fade and Obscured by granules
• Cytoplasm is more evident: basophilic (pale blue)
• N:C ratio 4:1 or 5:1
• Contain abundant dark azurophilic (primary)
granules that overlie both nucleus and cytoplasm
• These non-specific granules contain peroxidase
• Constitutes 1 - 2% BM cells.
Myeloblast Vs Promyelocyte
Myeloblast
Promyelocyte
Type I: Meyeloblast
• Large number of azure granules and nucleoli
Type II: Meyeloblast with few azure granules
Neutrophil Myelocyte




Last stage capable of cell division
First stage to differentiate into eosinophil, basophil, or neutrophil
10-18m in diameter and round.
Sometimes divide in to early and late myelocytes
 Nucleus:
• Condensed, oval, slightly indented and eccentric
• Chromatin is coarse
• Nucleoli are absent
 Cytoplasm: Light pink
• Primary granules production ceases
• Secondary granules production begins
• N:C ration is about 2:1
 6% to 17% of marrow cells
Myelocytes
 Two early myelocyte (similar to
promyelocyte except several light
areas in their cytoplasm where specific
granules are beginning to appear
 Three late myelocyte (arrow)
few primary granules and
lavender secondary granules
Neutrophil Metamyelocyte (Juvenile cell)
 Observed in bone marrow or peripheral blood in infections
 No longer capable of division
 14-16m in diameter
 Nucleus: Major morphologic change
•
Eccentric, condensed and indented or kidney-bean shaped
• Chromatin increasingly clumped
• Stains darker
• Nucleoli absent
 Cytoplasm: abundant and pale or pink
• Secondary granules are more evident
• Tertiary (gelatinase) granules synthesis begins
• May contain few primary granules
• N:C ratio: 1:1
Constitute 3 - 20% of marrow cells
Myelocyte Vs Metamyelocyte
Early neutrophil myelocytes
Late myelocytes
Metamyelocytes
Neutrophil band (Stab cell)
 Youngest granulocyte normally found in peripheral blood and
recommended by to be counted with Seg. Neutrophil by CLSI
 Nucleus is elongated, curved and very clumped
• “U” or “C” or “S” shaped or twisted
 >5% in peripheral blood = abnormal (0-5%)
• May be due to infection
 Cytoplasm is abundant with many fine granules
• More secondary granules are evident
• Tertiary granules continue to be formed
• Secretory granules may begin to be forms
• Is pink or colorless
• N;C ratio: 1:2
 9% to 32% of marrow cells
Segmented granulocyte (Seg)





Purpose is to engulf and destroy bacteria
50-70% circulate in peripheral blood
7% to 30% of nucleated cells in the bone marrow
Capable of diapedesis and phagocytosis
Seg to band ratio: 10:1
 Nucleus is pinched into segments connected with a fine filament
• Chromatin is coarse
• 2-5 lobes are observed
• Most recommend if a filament is not seen, call it band
 Abundant pink cytoplasm with secondary granules, do not
overlay the nucleus …. Tertiary granules
 Secretory granules continue to be formed
Hypersegmented N.
Eosinophil development
 Eosinophils mature in the same manner as neutrophils.
 Arise from CMP through interactions of cytokines IL-3, Il-5, CSF-GM and three
transcription factors (GATA-1, PU.1 and c/EBP).
• IL-5 is critical for growth and survival
 E. promyelocytes can be identified with cytochemically due to presence of CharcotLeyden crystal protein in their primary granules
• Granule are at first bluish and later mature into orange granules
 E. Myelocyte: identified with light microscope.
• Large, pale, reddish-orange secondary granules
 1-3% of marrow cells and peripheral blood. (up to 0.4 x 109/L) in peripheral blood
Mature Eosinophil
 Size and shape: 10-16m in diameter, slightly larger than neutrophil
 Nucleus: Eccentric and usually bilobed
 Rarely single- or tri-lobed and contains dense chromatin masses.
 Eosinophils with more than two nuclear lobes are seen in
• Vitamin B12 and folic acid deficiency
• In allergic disorders
 Cytoplasm:
• Densely filled with orange-pink specific granules.
• The granules are
• Uniform in size
• Large and individualized, Do not cover the nucleus
• Highly metabolic and contain histamine and other substances
Basophilic Granulocyte and Precursors
 Early maturation of the basophilic is similar to that of the neutrophil
Mature Basophil
 Size: Somewhat smaller than eosinophils
• Measuring 10-14m in diameter
 Nucleus: Indented giving rise to an S pattern.
• It is difficult to see the nucleus
• It contains less chromatin and is
• Masked by the cytoplasmic granules.
 Cytoplasm: Pale blue to pale pink
• contains granules that often overlie the nucleus but do not fill the cytoplasm as
completely as the eosinophils granules do
• Basophil granules are water soluble, may be washed if BF washed too much
• 0-2% in peripheral blood and <1% marrow cells
Name the Granulocyte precursors
Band
Promyelocyte
Myelocyte
Development of Monocytes and Macrophages
 Cells of the macrophage system are formed from the progenitor cells in the bone
marrow.
 These cells are derived from the CFU-GM, which can differentiate into either the
CFU-M and develop into a monocyte or macrophage or CFU-G and develop into a
segmented neutrophil.
 The chromatin is clumped, although the clumps are smaller and more elongated than
in neutrophils.
 The shape of the nucleus of the monocyte may be round or oval, but it is frequently
convoluted or twisted.
 Functionally, monocytes and macrophages have phagocytosis as their major role,
although they also have regulatory and secretory functions.
Monoblast
 Monoblast cannot be differentiated from the myeloblast on morphologic or
histochemical criteria
 Size: 15-20m in diameter.
 Nucleus: Round or oval and at times notched and indented
• The chromatin is delicate blue to purple stippling with small regular, pink, pale
or blue parachromatin areas
• Pale blue, large and round nucleoli (3-5 in #)
 Cytoplasm: Relatively large in amount
• May contains a few azurophilic granules (rare)
• Stains pale blue or gray
• Auer bodies may be observed
• The cytoplasm filling the nucleus indentation
is lighter in color than the surrounding cytoplasm
Promonocyte
 Is the earliest monocytic cell recognizable as belonging to the monocytic series
 is capable of mitotic division
 Its product, the mature monocyte, is only capable of maturation into a macrophage
 Size: 12-20m in diameter.
 Nucleus: Large, ovoid to round, convoluted, grooved, and indented
• The chromatin forms a loose open network containing a few larger clumps
• There may be two or more nucleoli.
 Cytoplasm:
• sparse, gray-blue, contains
fine azurophilic granules
 N:C ratio is about 3:1
Monocyte
 Size: 12-20m in diameter.
 Nucleus: Pale, Eccentric or central and has different shapes
• Brainy convolutions to lobulated and S shaped (often
lobulated), kidney shaped, twisted
• The chromatin network consists of fine, pale, loose, linear
threads producing small areas of thickening at their junctions
• No nucleolus is seen
 Cytoplasm:
• Abundant, opaque, gray-blue with moderate granules
• unevenly stained and may be vacuolated
• N:C ratio 1:1
Monoblast
Monocyte
maturation
1
Promonocyte
Monocyte
2
Monocyte
Tissue Monocyte/Macrophage
3
Formation of lymphocytes
(Lymphopoiesis)
Lymphopoiesis
 Lymphocytes are derived from committed stem cells that originate from pluripotent
stem cell.
 Early lymphoid cells further differentiates into B. & T.lymphocytes.
B LYMPHOCYTES
 Developed in bone marrow or fetal liver
 Maturation culminates in migration to other lymphoid organs and tissues (e.g.
spleen, gut, liver , tonsils, lymph nodes)
 They proliferate and mature into antibody forming cells.
T lymphocytes
 Differentiation and maturation take place in thymus,
 These thymocytes loose their antigenic surface molecules and finally mature into
• Helper/ effector T lymphocytes and
• Suppressor T lymphocytes
Lymphocyte
Maturation
1
Lymphoblast:
• Round or oval nucleus
with 1 or 2 nucleoli,
2
3
Prolymphocyte:
Mature Lymph:
• Oval or slightly
• Round or oval nucleus,
indented nucleus with 0may have an
1 nucleoli
indentation (cleft).
• Delicate chromatin pattern
• cytoplasm is medium blue
and may have a darkerblue border,
• No granules are present.
• Slightly condensed
chromatin
• Nucleoli are not visible.
• Clumped chromatin,
• Cytoplasm is medium
blue with a thin, darker
blue rim.
• Cytoplasm is light sky
blue and very scanty.
Plasma Cells
Plasma cells
 Little capacity to undergo mitosis.
 ultimate stage for synthesis and secretion of
antibodies
• Main purpose is to make antibodies
• B cell becomes a plasma cell
• Plasmablast->proplasmacell->plasmacyte
• Mature plasma cell
• Nucleus is round and eccentric with clumped
chromatin
• Cytoplasm is dark blue with pale perinuclear
zone
• Cornflower blue
Production of Specific Cell lineages
3. Thrombocyte Production (Thrombopoiesis)
Formation of platelets (Thrombopoiesis)
 Platelets are produced in the bone marrow by fragmentation
of the cytoplasm of megakaryocytes
 Stimulated by Thrombopoietin
 The megakaryoblast produces megakaryocytes, distinctive
large cell that are the source of circulating platelets.
 Megakaryocyte development takes place in a unique
manner.
• These cells undergo endomitosis, whereby the cell does not
divide; instead, it becomes larger and the nucleus becomes
polyploid, as much as 64 N.
Thrombopoiesis
Three stages of maturation of megakaryocytes
1. Basophilic stage, megakaryocyte is small, has diploid
nucleus and abundant basophilic cytoplasm.
2. Granular stage, here the nucleus is more polyploid,
cytoplasm is more eosinophilic and granular
3. Mature stage, megakaryocyte is very large, abundance
of granular cytoplasm. It undergoes shedding to form
platelets (thrombopoiesis)
stages of megakaryocyte progenitors
• Reaches its full ploidy level by the end of the MK-II stage.
• At the MK-III stage, the megakaryocyte is easily recognized at
10× magnification
Platelet maturation
Bone Marrow
Megakaryocytic
Platelet
Thrombocyte
maturation
Giant Platelet
Any questions?
Lymphopoiesis




The precursor of the lymphocyte is believed to be the
primitive mulipotential stem cell that also gives rise to the
pluirpotenital myeloid stem cell for the granulocytic,
erythyroid, and megakaryocytic cell lines
Lymphoid precursor cells travel to specific sites
There, they differentiate into cells capable of either
expressing cell-mediated immune responses or
secreting immunoglobulins
The influence for the former type of differentiation in
humans is the thymus gland;
 the resulting cells are defined as thymus-dependent
lymphocytes, or T cells.
Lymphopoiesis cont’d

The site of the formation of lymphocytes with the
potential to differentiate into antibody-producing cells
has not been identified in humans, although it may be
the tonsils or bone marrow

In chickens it is the bursa of Fabricius, and for this
reason these bursa-dependent lymphocytes are called
B cells

B cells ultimately differentiate into morphologically
distinct, antibody-producing cells called plasma cells.
Lymphocytes and Precursors
Lymphoblast




Size:
 10-20m in diameter.
Nucleus:
 Central, round or oval
 the chromatin has a stippled pattern
 The nuclear membrane is distinct and one or two pink
nucleoli are present and are usually well outlined
Cytoplasm:
 Non-granular and sky blue
 may have a deep blue border
 It forms a thin perinuclear ring.
N:C ratio 4:1
Prolymphocyte



Size:
 9-18m in diameter.
Nucleus:
 Oval but slightly indented
 may show a faint nucleolus
 The chromatin is slightly condensed into a mosaic
pattern.
Cytoplasm:
 Gray blue, mostly blue at the edges
 may show a few azurophilic granules and vacuoles
Lymphocytes


There are two varieties
the morphologic difference lies mainly in the amount of
cytoplasm
Small Lymphocyte


Size:
 7-18m in diameter.
Nucleus:
 round or oval to kidney shaped
 occupies nine tenths of the cell diameter
 The chromatin is dense and clumped
 A poorly defined nucleolus may be seen.
Lymphocytes cont’d



Cytoplasm:
 It is basophilic and forms a narrow rim around the
nucleus or at times a thin blue line only with few
azurophilic red granules
N:C ratio is 4:1
Distinguishing characteristics of a small lymphocyte:
 clumping of chromatin around the nuclear membrane
may help to distinguish this from a nucleated red cell
Large Lymphocyte



Size:
 9-12m in diameter
Nucleus:
 the dense, oval, or slightly indented nucleus is
centrally or eccentricity located
 Its chromatin is dense and clumped.
Cytoplasm:
 Abundant
 gray to pale blue, unevenly stained, and streaked at
times
 A few azurophilic granules are contained in 30-60% of
the cells.
 These are large granular lymphocytes (LGLs).
Large Lymphocyte cont’d


N:C ratio is 4:1
Distinguishing characteristics: Cytoplasm is mor
abundant with tendency for azurophilic granules
Formation of platelets (Thrombopoiesis)




Platelets are produced in the bone marrow by
fragmentation of the cytoplasm of megakaryocytes
The precursor of the megakaryocyte-the
megakaryoblast-arises by a process of differentiation for
the hemopoietic stem cell
The megakaryoblast produces megakaryocytes,
distinctive large cell that are the source of circulating
platelets.
Megakaryocyte development takes place in a unique
manner.
 The nuclear DNA of megakaryoblasts and early
megakaryocytes reduplicates without cell division, a
process known as endomitosis.
Thrombopoiesis cont’d



As a result, a mature megakaryocytes has a polyploidy
nucleus, that is, multiple nuclei each containing a full
complement of DNA and originating from the same
locust within the cell.
Mature megakaryocytes are 8 n to 36 n.
The final stage of platelet production occurs when the
mature megakaryocyte sends cytoplasmic projections
into the marrow sinusoids and sheds platelets into the
circulation.
Thrombopoiesis cont’d



It takes approximately 5 days from a megakaryoblast to
become a mature megakaryocyte.
Each megakaryocyte produces from 1000 to 8000
platelets.
The platelet normally survives form 7 to 10 days in the
peripheral blood.
Morphology of the Platelets and their
Precursors
Megakaryoblast
 Size:
 ranges from 10-30m in diameter.
 The cell is smaller than its mature forms but larger
than all other blast cells.
 Nucleus:
 the single, large, oval or indented nucleus has a loose
chromatin structure and a delicate nuclear membrane
 Multi-lobulated nuclei also occur representing a
polyploid stage.
 Several pale blue nucleoli are difficult to see
 The parachromatin is pink.
Megakaryoblast cont’d

Cytoplasm:
 the cytoplasm forms a scanty, bluish, patchy, irregular
ring around the nucleus
 The periphery shows cytoplasmic projections and
pseudopodia like structures.
 The immediate perinuclear zone is lighter than the
periphery.
Promegakaryocyte


Size:
 ranges from 20-50m in diameter.
 It is larger than the megakaryoblast
 in the process of maturation it reaches the size of the
stage III cell.
Nucleus:
 large, indented and poly-lobulated.
 the chromatin appears to have coarse heavily
stained strands and may show clumping
 The total number of nucleoli is decreased and they
are more difficult to see than in the blast cell.
 The chromatin is thin and fine.
Promegakaryocyte cont’d

Cytoplasm:
 intensely basophilic
 filled with increasing numbers of azurophilic
granules radiating from the golgi apparatus toward
the periphery sparing a thin peripheral ring that
remains blue in color.
Granular Megakaryocyte

The majority of the megakaryocytes of a bone marrow
aspirate are in stage III which is characterized by
progressive nuclear condensation and indentation and the
beginning of platelet formation within the cytoplasm.

Size:
 ranges from 30-100m in diameter
 is the largest cell found in the bone marrow.
Cytoplasm:
 a large amount of polychromatic cytoplasm produces
blunt, smooth, pseudopodia-like projections that contain
aggregates of azurophilic granules surrounded by pale
halos
 These structures give rise to platelets at the periphery of
the megakaryocytes.

Platelets


Size:
 varies from 1-4m in diameter.
Nucleus:
 no nucleus is present.
 In Wright - Giemsa stained films, platelets appear as
small, bright azure, rounded or elongated bodies with
a delicately granular structure.
Review Questions/Summary
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
What is hemopoiesis and how is the process regulated?
What are the hemopoietic tissues during fetal life, in
infancy, in childhood and in adulthood?
What are the effects of the hormone erythropoietin on
red cell development and maturation.
Describe the microenvironment briefly.
Explain megaloblastic erythropoiesis.
Describe general Characteristic feature of cells during
maturation (nuclear , cytoplasmic, etc )
State the composition of blood.
State the main functions of blood.
List main characteristics of blood.
What is extramedulary hemopoiesis and when does it
occur?
Summary