You are now at the beginning of the WBC Basics study
Leukocytes or WBCs are found in a thin gray layer known
as the buffy coat in centrifuged blood. Above the leukocytes
lie the platlets.
Leukocytes are primarily defensive, but also have important
sanitation and recycling duties.
Before reviewing the origin and development of WBCs let
us first look at the mature WBC population normally found
in the peripheral blood (buffy coat), including neutrophils,
eosinophils, basophils, monocytes, and lymphocytes.
Neutrophils The mature neutrophil (12-15u dia)
is characterized by segmentation into 2-5 lobes. The chromatin
is dense and clumped with distinct lighter areas of parachromatin.
The cytoplasm is lightly eosinophilic with variable numbers
of light staining "neutral" granules and a few and a few
azurophilic 1 granules, persistent from earlier stages.
Neutrophils are important in the inflammatory process (as
phagocytes and mediators of inflammatory reactions).
The term neutrophil refers to the cell type
not to the degree of differentiation.
Eosinophils The large orange granules of the
eosinophil make the eosinophil the most readily recognizable
cell in the blood. The eosinophil (12-15u diameter has chromatin
similar to that of a neutrophil, but usually fewer (2-3)
Normally 0-6% eosinophils are found in the peripheral blood.
The eosinophil specific granules contain rhomboid crystals
by EM. This core contains Major Basic Protein (MBP), known
to be toxic to several parasites (helminths, microfilariae;
schistomiasis), and some mammalian cells.
Compare the granules of the neutrophil (at
left) with those of the eosinophil (at right).
Basophil The purple-black, often large coarse
irregularly sized granules of the basophil are chacteristic
and may obscure the nucleus of this relatively uncommon
cell. The mature nucleus is segmented into 2-3 lobes.
Basophils (12-15u dia) contain heparin and large amounts
Basophils are active participants in hypersensitivity reactions.
The mature nucleus is segmented into 2-3 lobes.
Monocytes are the largest (12-20u dia) cells
normally found in the peripheral blood. Monocytes have abundant
blue-gray, sometimes very pale pink cytoplasm with small,
generally indistinct, granules. One may see fine reddish
granules of variable prominence. Occasionally, large azurophilic
granules will be seen.
Cytoplasmic vacuoles are often seen. The nucleus is irregular,
frequently with delicate folds and often lobulated. The
chromatin is fine and lacey, sometimes described as reticular.
The mature monocyte has no nucleoli.
Monocytes are phagocytes and frequently contain vacuoles.
Monocytes can migrate into tissues where they are known
Monocytes are central to the "battle" management of inflammatory
The peripheral blood normally contains 0-l0% monocytes.
Compare the chromatin and the size of the monocyte (top)
with the lymphocyte.
Lymphocytes vary greatly in size (7-20m
dia) and in nuclear and cytoplasmic character. The small
lymphocyte (7-12m dia) has a round-oval nucleus with dense
clumped "smudgy" chromatin; no visible nucleolus. Scanty
light blue cytoplasm, while usually agranular, may contain
a few small red granules. Contrast the chromatin of the
lymphocyte and neutrophil. The lymphocyte at right is 15-18m
Normal peripheral blood lymphocyte percentages
vary from l5-60%.
Lymphocytes with peripherially clumped chromatin and often
deep blue cytplasm similar to plasma cells are termed plasmacytoid
Terminally differentiated lymphocytes or plasma
cells (left panel) are rarely found in the peripheral blood.
Young or stimulated lymphocytes (right panel) are larger
and have relatively more cytoplasm and larger nuclei than
mature or unstimulated cells.
Some larger lymphocytes with moderate amounts
of cytoplasm and distinct red granules are known as large
granular lymphocytes (LGL).
Knowledge of the relative and absolute numbers of the
various WBCs in the peripheral blood (PB) together with
a qualitative evaluation of the morphology is key to assessing
The morphologic identification of a consecutive series
of WBCs, by eye or automated instrument, results in a differential
count, in which the relative number of each cell is expressed
as a percentage. This may be deceiving.
Therefore, more important than the "Diff" is the calculation
of the absolute count.
While examining your own blood you find:
a WBC (8,000 µ L) with
25 % neuts
Is this normal? Do you have too few neutrophils? too many
lymphocytes, eosinophils and basophils?
The myeloid, monocytic, and lymphocytic leukocytes of
the peripheral blood originate, and for the most part, mature
in the bone marrow.
In the marrow microenvironment numerous hematopoietic growth
factors influence the selection and stimulation of stem
cells to the production of leukocytes.
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