Cui Dongmei. Atlas of Histology: with functional and clinical correlations. 1st ed

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Erythropoiesis

Figure 8-10A Proerythroblasts

Figure 8-10B Basophilic Erythroblasts

Figure 8-10C Polychromatophilic Erythroblasts

Figure 8-11A Orthochromatophilic Erythroblasts

Figure 8-11B Reticulocytes

Figure 8-11C Clinical Correlation: Reticulocytosis

Thrombopoiesis

Figure 8-12A Promegakaryocytes

Figure 8-12B Megakaryocytes

Figure 8-12C Clinical Correlation: Essential Thrombocytosis

Granulocytopoiesis

Figure 8-13A A Representation of Granulocytopoiesis

Figure 8-13B Overview of Stages of Granulocytes in Development

Figure 8-14A–C Promyelocytes, Myelocytes, and Metamyelocytes

Figure 8-15A–C Stab (Band) Cells, Bone Marrow Cells, and Bone Marrow

Figure 8-16 Developing Blood Cells in the Hematopoietic Compartment

Synopsis 8-2 Hematopoiesis

Synopsis 8-3 Pathological and Clinical Terms for Mature and Developing Blood Cells

Peripheral Blood Cells

Introduction and Key Concepts for

Peripheral Blood Cells

Blood smears are prepared so that the morphology of the

formed elements can be assessed and the relative numbers of

the leukocytes can be calculated (differential leukocyte count).

If a person is anemic, examination of erythrocyte morphology

can help classify the type of anemia. If a person has an elevated

leukocyte count, a differential white cell count can provide

valuable information toward determining what kind of infec-

tion or leukemia the person has. All formed elements serve criti-

cally important functions. Erythrocytes function in transport of

respiratory gases, platelets function mainly in hemostasis, and

leukocytes function in various ways to protect from infection

by a wide variety of potential pathogenic organisms.

ERYTHROCYTES deliver oxygen from the lungs to all the

tissues of the body, although they are also involved in carbon

dioxide transport and pH regulation. Because erythrocytes

are anucleate and lack membrane-bounded organelles, their

internal structure is homogeneous. An erythrocyte is essen-

tially a plasmalemma bag containing a highly concentrated

(30%) hemoglobin solution. In addition, erythrocytes have a

membrane-associated complex of cytoskeletal proteins that ren-

ders the biconcave disk shape (Figs. 8-2A to 8-3B).

PLATELETS (thrombocytes) are small fragments of cytoplasm

with a complex and highly organized structure. They normally

range in number from 200,000 to 400,000/μL. If the plate-

let number falls below 60,000/μL (“thrombocytopenia”), the

integrity of the smallest blood vessels is compromised. Platelets

function to minimize loss of blood when there is a breach in the

circulatory system (Fig. 8-2B).

LEUKOCYTES are much less abundant than erythrocytes,

4,500 to 11,000/μL in contrast to about 5 million/μL. How-

ever, white cell numbers can increase markedly in some cir-

cumstances, such as infection or leukemia. Leukocytes have a

wide range of life spans—from a few days (neutrophils) to years

(some lymphocytes). All leukocytes are involved in defense

against microorganisms and other foreign agents and in tissue

responses to injury. Usually, they perform their functions only

after leaving the blood stream and entering the conventional

connective tissue through processes of attachment to endothe-

lial cells and active movement through gaps in the endothe-

lium (diapedesis). Leukocytes are constantly released from the

bone marrow to be delivered by the cardiovascular system to

the vascular beds of all peripheral tissues. Leukocytes are clas-

siﬁ ed as either nongranular (agranular) or granular depending

on whether speciﬁ c cytoplasmic granules are evident when the

cells are stained with Romanowsky-type stains like Wright

stain. The three types of granulocytes—basophils, eosinophils,

and neutrophils—are named and identiﬁ ed by the staining reac-

tion of their speciﬁ c granules. The two types of nongranular

leukocytes, lymphocytes and monocytes, also have granules,

but the granules are only nonspeciﬁ c granules (lysosomes). All

granulocytes are terminal cells; that is, they will never again

divide because they have lost that capacity during differentia-

tion. Monocytes and lymphocytes have the potential for further

division.

Lymphocytes are the second most abundant leukocyte,

amounting to about 25% to 33% of leukocytes. These are the

cells that mediate speciﬁ c immunity against foreign molecules

and organisms. B lymphocytes produce immunoglobulins, and

their derivatives, plasma cells, are specialized to secrete solu-

ble antibodies. T lymphocytes are the agents of cell- mediated

speciﬁ c immune responses, and they comprise several types.

Among these, cytotoxic T cells function to kill virus-infected

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host cells, and helper T cells and suppressor T cells regulate

immune responses (Fig. 8-4 A,C). For null cells, see Chapter

10, “Lymphoid System.”

Monocytes, the largest of the leukocytes, constitute about

3% to 7% of circulating white blood cells. Monocytes are not

functionally or structurally mature when they are circulating in

blood. Rather, they are an intermediate form of a cell lineage

that starts differentiation in the bone marrow (like all blood

cells) but does not fully complete differentiation until arrival in a

peripheral tissue. There are several functional cell types that are

derived from monocytes, including tissue macrophages, Kupffer

cells, microglial cells, osteoclasts, and antigen-presenting cells

(Fig. 8-4B).

Neutrophils are by far the most abundant leukocytes. Typi-

cally 54% to 62% of leukocytes are mature neutrophils, and an

additional 3% to 5% of leukocytes are immature (band) forms.

Neutrophils are the main cellular weapon for destroying bac-

teria, and the total number of circulating neutrophils can rise

sharply in response to bacterial infections. Once a neutrophil

makes contact with a bacterium, the neutrophil attaches to the

bacterium and engulfs it (phagocytosis) within a phagosome.

The primary and secondary granules of the neutrophil fuse with

the phagosome, thereby exposing the bacterium to an array

of bactericidal compounds and enzymes. Another bacteria-

killing mechanism employed by neutrophils is the generation of

reactive oxygen compounds in a process termed the respiratory

burst (Figs. 8-5 to 8-6).

Eosinophils amount to about 1% to 3% of circulating leuko-

cytes, and, like basophils, their numbers tend to rise in response

to parasitic infections and allergic reactions. The functions of

eosinophils are not fully understood, but they clearly function

in defense against infection by parasitic worms such as schisto-

somes. Eosinophils are recruited to sites of parasitic infection,

and some of their granule contents (e.g., major basic proteins)

are highly toxic to parasites. They also appear to function in

dampening and limiting inﬂ ammation at sites of allergic reac-

tions (Fig. 8-7A).

Basophils are the least numerous (<1%) of the leukocytes.

Basophils are functionally similar to the mast cells found in

connective tissue. Neither cell type functions by phagocytosis,

so they are quite unlike neutrophils. Instead, their functions in

defense against microbial invasion are indirect. When activated,

they secrete (or exocytose) a variety of inﬂ ammatory media-

tors from their granules and synthesize and release a number of

arachidonic acid derivatives, such as leukotrienes and prosta-

glandins. These signaling molecules intensify inﬂ ammation by

(1) increasing local blood ﬂ ow, (2) enhancing leakage of plasma

proteins from blood, (3) promoting recruitment of other leuko-

cytes to a site of infection, and (4) enhancing the activity of the

other leukocytes (Fig. 8-7).

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Figure 8-1. Overview of peripheral blood cell types (mature blood cells), blood smear. Wright stain, 1,569

Blood is a specialized connective tissue composed of blood cells suspended in intercellular ﬂ uid (or plasma). Blood cells include eryth-

rocytes (red blood cells), platelets (thrombocytes), and leukocytes (white blood cells). Erythrocytes are the most numerous. They are

biconcave disk–shaped cells without nuclei and are important in transportation of gases. Platelets are very tiny cell fragments that have

no nuclei, cannot reproduce, and come from huge cells called megakaryocytes (Figs. 8-9B and 8-12). Platelets play an important role in

hemostasis. Leukocytes can be classiﬁ ed as either agranulocytes or granulocytes based on the absence or presence of speciﬁ c granules in

their cytoplasm. Granulocytes are also called polymorphonuclear leukocytes because of the multiple lobes of their nuclei, but the term

is often used speciﬁ cally for neutrophils. (1) Agranulocytes lack speciﬁ c cytoplasmic granules but have the ability to divide. Lympho-

cytes and monocytes fall into this category. Lymphocytes are the smallest cells in the leukocyte series. Each has a round nucleus and a

small amount of cytoplasm. They can be found outside of the blood stream in lymphoid organs and connective tissues. Lymphocytes

can be classiﬁ ed as T lymphocytes, B lymphocytes, and null cells. They are associated with immunological defense functions. B lym-

phocytes can further differentiate into plasma cells (see Figs. 4-2B and 4-3A,B). Monocytes are the largest cells in the leukocyte series.

They have large, elongated, and often kidney-shaped nuclei. They can differentiate into phagocytes, including macrophages, Kupffer

cells, microglia, and osteoclasts. (2) Granulocytes contain speciﬁ c granules in their cytoplasm, and their nuclei are segmented. They are

terminal cells without the capability to divide further. Granulocytes include neutrophils, eosinophils, and basophils. Neutrophils are

the most abundant leukocytes in circulating blood. Each cell has a multilobed nucleus and a pale pink cytoplasm that contains primary

and secondary (speciﬁ c) granules. Neutrophils play an important role in defense against bacterial infection.

Eosinophils contain large,

speciﬁ c granules that stain red with eosin dye. They usually have a bilobed, or occasionally a trilobed, nucleus. Eosinophils function

in controlling allergic reactions and in combating parasitic infections. Basophils are the rarest of the leukocytes (<1%). They contain

large, speciﬁ c granules that are deep violet with a Wright stain. Each basophil has a nucleus with two to three lobes that are not com-

pletely separated. Basophils, along with mast cells, are instigators of allergic reactions (see the introduction to this chapter).

D. Cui

Erythrocytes

Platelets

Neutrophils

Monocytes

Eosinophils

Lymphocytes

Basophils

Agranulocytes Granulocytes

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Erythrocytes and Platelets

CLINICAL CORRELATION

Figure 8-2C.

Sickle Cell Anemia, Blood Smear. W

right

stain, 1,035

Sickle cell anemia is an autosomal recessive disorder character-

ized by the production of defective hemoglobins, which aggregate

and polymerize when deoxygenated. The red blood cells become

longer and curved, similar to a “sickle.” Sickle cells block blood

vessels, causing ischemia of the tissues and severe pain. Symptoms

and signs, which start in early childhood, include anemia, vasooc-

clusive complications, and chronic hyperbilirubinemia. This dis-

ease is more common in people of African, Turkish, Arabian, and

Mediterranean ancestry. Dehydration, infection, hypertonicity,

and decreased pH can trigger an onset. In a sickle cell patient, the

average life span of red blood cells is 17 days, as compared to 120

days in normal persons. Bone marrow transplants can cure a small

number of people. Normal and sickle cell forms are shown here.

Sickle-shaped

red blood cells

Inmature red

blood cell

Normal red

blood cell

Figure 8-2A. Erythrocytes (red blood cells), blood smear.

Wright stain, 1,576

Erythrocytes are the most abundant cells in blood. They have a

unique biconcave disk appearance (Fig. 8-3), are anucleate (without

nuclei), and have no organelles after they mature. Here, red blood

cells are seen as pink circles with pale centers in a Wright stain.

Erythrocytes are produced in the red bone marrow and are trans-

ported into the blood circulation through the walls of sinusoidal

capillaries in the marrow. Their life span is about 120 days. Aged

erythrocytes are destroyed by macrophages in the spleen, liver, and

bone marrow. Erythrocytes contain highly concentrated hemoglo-

bin (Hb). They appear bright red in color when oxygen content is

high and are more purple when they are depleted of oxygen. Their

function is to transport oxygen to peripheral tissues and carry car-

bon dioxide out of tissues. Hemoglobin binds with oxygen to form

oxyhemoglobin when the O

level is high (lung) and binds with CO

to form carbaminohemoglobin when the CO

level is high (tissue).

D. Cui

Erythrocytes

Erythrocyte

D. Cui

Granulomere

Hyalomere

Platelets

Figure 8-2B. Platelets (thrombocytes), blood smear. Wright

stain, 1,576; inset 1,570

Platelets, also called thrombocytes, are very small, lens-shaped frag-

ments of cells. They have some functional characteristics of whole

cells, even though they do not have nuclei. Each platelet has a surface

membrane covering cytoplasm that contains microtubules, micro-

ﬁ laments, mitochondria, and several types of granules. The central

region where granules stain purple is termed the granulomere; the

peripheral region, which stains light blue, is called the hyalomere.

The two main types of granules in platelets are alpha granules and

delta granules (dense bodies). These play a role in the adhesion and

aggregation of platelets in blood coagulation. If damage occurs to

the vascular endothelium, platelets adhere to the vessel wall, releas-

ing granules and aggregating to stop bleeding.

The absence of alpha granules can cause gray platelet syndrome,

whereas reduced numbers or absence of delta granules will lead

to storage pool deﬁ ciency.

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Erythrocytes

Platelet

Capillary endothelial cell

Figure 8-3B. Erythrocytes and a platelet in a small blood vessel. EM, 10,000

The lumen of this capillary (or venule) contains proﬁ les of several erythrocytes and a platelet. The erythrocytes in this thin section

present a variety of proﬁ le shapes owing to two effects: the random orientation of the plane of section and the ﬂ exibility that allows

the cells to bend in compliance with surrounding pressures. The platelet here is cut transversely through its biconvex shape, which

is maintained by microtubules arranged as a hoop at the edge of the disk. The magniﬁ cation of this view is not quite sufﬁ cient to

reveal the microtubules. It can be seen here that the platelet contains a variety of granules and tubules.

Figure 8-3A. Erythrocytes, small artery.

SEM, 1,140

This scanning electron micrograph demon-

strates the various shapes of the blood cells

contained in the lumen of a small artery.

The erythrocytes appear as biconcave disks;

that is, “doughnuts” with thin diaphragms

across the holes. By contrast, the leukocytes

are spherical, and the different types cannot

be distinguished. No platelets are visible in

this view. The inner layer of the artery wall is

tunica intima, composed mainly of endothe-

lium and a thin internal elastic lamina.

Erythrocytes

Internal elastic lamina

Endothelium

of small artery

Endothelium

of small artery

Leukocytes

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Leukocytes: Agranulocytes

CLINICAL CORRELATION

Figure 8-4C.

Chronic Lymphocytic Leukemia, Blood

Smear

. Wright stain, 736

Chronic lymphocytic leukemia (CLL) is a type of blood

cancer characterized by abnormally high numbers of mature

lymphocytes in certain tissues and peripheral blood. Lympho-

cytes inﬁ ltrate the liver, spleen, lymph nodes, and the bone

marrow. Signs and symptoms include petechiae (“pinpoint”

hemorrhages) in the skin and soft palate; enlargement of the

liver, spleen, and lymph nodes; anemia; fever; infections; bone

pain; and weight loss. In some patients, CLL will transform

into an aggressive lymphoma. The cause of CLL is not clear,

but it may be associated with chromosomal disorders, radia-

tion, benzene exposure, and chemotherapy. CLL progresses

slowly but is not considered curable. Treatment includes che-

motherapy and bone marrow transplant. In the peripheral

blood, CLL cells are small lymphocytes with clumped chro-

matin and little cytoplasm. Smudge cells, although not speciﬁ c

for CLL, are commonly seen on peripheral blood smears.

CLL

lymphocytes

Smudge cell

Neutrophil

Figure 8-4A. Lymphocytes, blood smear. Wright stain, 754;

inset 1,569

Most lymphocytes in the blood are small to medium-sized cells. Each

has a relatively large, round nucleus with a thin rim of cytoplasm (which

is often crescent shaped). Lymphocytes originate in the bone marrow

and thymus and circulate throughout the body in the blood and lymph

circulation systems. Lymphocytes are motile and play an important

role in immunological defense. They can be classiﬁ ed into B lym-

phocytes, T lymphocytes, and null cells based on their immunologic

functions. B lymphocytes are responsible for the humoral immune

response, in which immunoglobulins are secreted after they differenti-

ate into plasma cells. T lymphocytes are responsible for the cellular

immune response. T and B lymphocytes are morphologically indistin-

guishable in blood smears. Null cells are large cells that are morpholog-

ically similar to other lymphocytes but lack the characteristic surface

markers of the B and T cells (see Chapter 10, “Lymphoid System”).

D. Cui

Lymphocyte

Neutrophil

Lymphocyte

D. Cui

Lymphocyte

Neutrophil

Monocyte

Figure 8-4B. Monocytes, blood smear. Wright stain, 754;

inset 1,569

Monocytes are the largest agranular cells in the peripheral blood.

Each cell has a large, elongated nucleus, often assuming kidney or

horseshoe shapes. The cytoplasm of monocytes is blue-gray and con-

tains a variable number of dark blue-purple granules that are called

azurophilic granules, so named because they attract azure (blue-

purple) dyes in stains used for blood smears. Azurophilic granules

are lysosomes, so they are nonspeciﬁ c granules present in the cyto-

plasm of both agranular and granular leukocytes. They are distinct

from the speciﬁ c granules found in granular leukocytes. Monocytes

originate from the bone marrow and remain in the blood circulation

in an immature (precursor) state for 1 to 2 days. They then enter

peripheral tissues to complete their differentiation. They become

macrophages (tissue phagocytes) in connective tissue, Kupffer cells in

the liver, microglia in the nervous system, and osteoclasts in bones.

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Figure 8-5A. Neutrophils, blood smear. Wright

stain, 754; inset 1,569

Neutrophils are the most abundant cells in the leu-

kocyte series. They have a multilobed (two to ﬁ ve

interconnected lobes) nucleus and pale pink cyto-

plasm with many granules (or vesicles). There are

two main types of granules in neutrophils: primary

(nonspeciﬁ c) and secondary (speciﬁ c) granules.

Primary granules are azurophilic granules, which

are modiﬁ ed lysosomes. The neutrophils’ primary

granules are larger and less numerous than speciﬁ c

granules. Secondary granules (speciﬁ c or neutro-

philic granules) are more numerous than primary

granules, and they contain a variety of antibacterial

compounds. They stain lavender or salmon-pink

with Wright stain, but they are difﬁ cult to distin-

guish because of their small size. Like other granular

leukocytes, neutrophils are terminally differentiated

cells unable to divide. They play a primary role in

defense against bacterial and fungal infections.

D. Cui

Neutrophils

Neutrophilic

stab (band)

cell

Lymphocyte

Neutrophil

Neutrophilic granules

Lobes of nucleus

Capillary endothelium

Neutrophilic granules

Lobes of nucleus

Capillary endothelium

Figure 8-5B. Neutrophil in a capillary. EM, 11,000

This leukocyte ﬁ lls the lumen of the capillary in which it resides. Although the thickness of the section is only about one

two-hundredth of the diameter of the cell, the features of the neutrophil are readily apparent. Proﬁ les of three lobes of the nucleus

can be seen, and the cytoplasm has an abundance of small granules that vary in electron density. The shapes of the granules also

vary from spherical to rice shaped. It is difﬁ cult to unequivocally distinguish the two main types of granules strictly on the basis

of morphology. However, the smallest and most numerous granules are speciﬁ c (neutrophilic, secondary) granules, and the largest

granules are nonspeciﬁ c (azurophilic, primary) granules. The neutrophilic granules are difﬁ cult to discern in the light microscope

because their size is close to the limit of resolution of light microscopy.

Leukocytes: Granulocytes

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Figure 8-6. A representation of neutrophil phagocytosis of bacteria.

Neutrophils play a central role in cellular defense against bacterial and fungal infections. They are highly motile cells and respond

quickly to inﬂ ammation in cases of microbial invasion. Acute inﬂ ammation, one of the body’s defense mechanisms, occurs in the

very early stage of tissue response to injuring agents, such as bacteria and fungi. During acute inﬂ ammation, microvessels dilate,

and their permeability increases as a result of histamine and other inﬂ ammatory chemicals, which are released into the connective

tissue by mast cells (see Chapter 4, “Connective Tissue”). Neutrophils quickly enter tissues from the blood circulation by adhering to

activated endothelial cells of capillaries and venules at the site of the inﬂ ammation. Bacteria are neutralized by several mechanisms,

which include the complement system and antibodies. Neutrophil phagocytosis of bacteria occurs in several steps: (1) Recognition:

The process begins with recognition of the bacterium by opsonins (IgG and complement C3b fragments) that coat the bacterium and

render it more susceptible to phagocytes. (2) Receptor binding: Fc receptors of neutrophils recognize and bind IgG that has bound to

the bacterium, or complement C3b receptors bind C3b fragments on the surface of the bacterium. (3) Pseudopod extension: Pseudo-

pods are slender cytoplasmic processes of neutrophils, which engulf (or “phagocytose”) the bacterium that has been recognized and

bound by receptors. (4) Formation of phagosome: The engulfment of the bacterium sequesters it in a membrane-bound vesicle, the

phagosome (food vacuole). (5) Killing and digestion of bacterium: Immediately after or even during formation of the phagosome,

the proton pumps in the membrane of the phagosome generate an acidic pH; both primary and secondary neutrophil granules fuse

with the phagosome and release their components into the phagosome to kill the bacterium and break down the constituents (pro-

teins, carbohydrates, nucleic acids) of the bacterium. Lysosomal enzymes and other products may leak into the extracellular space,

causing damage to endothelial cells and nearby tissues. (6) Formation of the residual body: Most of the remaining digested materials

form residual bodies (vesicles containing leftover products of indigestible materials after fusion with the contents of a lysosome)

inside the cells. (7) Cell death: Soon after neutrophils have ﬁ nished their job of killing and digesting bacteria, they die. The dead

neutrophils may be phagocytosed by macrophages, or they may accumulate locally with tissue debris and ﬂ uid to form pus.

Neutrophils use oxidative and nonoxidative mechanisms in killing bacteria and destroying other microbes. The oxidative mecha-

nism, also known as respiratory burst or oxygen-dependent mechanism, involves generation of hydrogen peroxide by the NADPH

(nicotinamide adenine dinucleotide phosphate) oxidase system and generation of hypochlorous acid by myeloperoxidase (components

of primary granules). The nonoxidative mechanism is involved in phagocytosis in the following manner: Primary and secondary gran-

ules fuse with the phagosome, and their granule components are released directly onto the microbe (see above steps 4 and 5). These

components include defensins, neutral serine protease, and lysozyme from the primary granules as well as lactoferrin and lysozyme

from the secondary granules. They perform their antimicrobial function by disrupting the phagosomal membrane, degrading bacterial

membranes, breaking down the protein and carbohydrate of the bacterium, and binding iron (which is needed for bacterial growth) to

prevent bacterial growth. Both oxidative and nonoxidative mechanisms work in concert to facilitate killing of the microbes.

D. Cui

Neutrophils

3. Pseudopod extension

2. Receptor binding

1. Recognition

4. Formation of phagosome

5. Killing and digestion

of bacterium

6. Formation of

residual body

7. Cell death

Fc receptor

Antibody

of IgG

Pseudopod

Bacterium

Residual body

Phagosome

A pathologic condition known as myeloperoxidase deﬁ ciency is caused by a defect in the NADPH oxidase complex. This

condition results in the inability to produce “superoxides” in neutrophils and other phagocytic cells. Affected individuals are

unable to kill invading microbes that are normally engulfed by these phagocytic cells. People with this defect can have frequent

and prolonged bacterial and fungal infections.

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SYNOPSIS 8-1 Life Spans, Counts, and Sizes of Blood Cells

Leukocytes ■ : Total number count is 4,500 to 11,000/mm

Erythrocytes

■ : Life span is about 120 days, count is 4,200,000 to 5,900,000/mm

(male 4,500,000–5,900,000/mm

; female

4,200,000–5,400,000/mm

); size is 7 to 8 μm (in diameter).

Platelets (thrombocytes)

■ : Life span is 8 to 12 days, count is 150,000 to 400, 000/mm

; size is 1 to 4 μm.

Monocytes

■ : Duration in circulation is a few hours to a few days before differentiating (a macrophage’s life span is up to

several months); count is 200 to 900/mm

; size is 12 to 15 μm.

Lymphocytes

■ : Life span is a few days to years; count is 1,000 to 4,000/mm

; size is 6 to 12 μm.

Neutrophils

■ : Duration in circulation is a few hours, life span is about 8 days; count is 3,500 to 7,000/mm

; size is 9 to 12 μm.

Eosinophils

■ : Life span is uncertain, likely a few days; count is 50 to 450/mm

; size is 9 to 14 μm.

Basophils

■ : Life span is uncertain, likely a few days; count is 0 to 200/mm

; size is 8 to 10 μm.

Clinical lab blood counts measure

■ total number count of white blood cells ([WBCs] leukocytes/mm

) and differential

counts (percent of each type of leukocyte [Table 8-1]). Absolute numbers of WBCs can be calculated by multiplying total

number/mm

times percent of each type of leukocyte.

Shift to left

■ : Increase in number of immature leukocytes (especially neutrophils in band forms), which suggests high

demand because of infection or acute inﬂ ammation (normal range of band leukocyte is 2%–6%).

Shift to right

■ : Absence of immature leukocytes in differential count of leukocytes.

Figure 8-7A. Eosinophil, blood smear. Wright stain,

754; inset 1,569

Eosinophils have a two- to three-lobed (segmented) nucleus,

numerous speciﬁ c (eosinophilic) granules, and a few azuro-

philic granules in the cytoplasm. Speciﬁ c granules contain

acid hydrolases, peroxidase, histaminase, basic protein and

eosinophil cationic proteins, which have antihelminthic

properties. Azurophilic granules contain mainly lysosomal

enzymes. Normally, the bone marrow contains a large

reserve pool of eosinophils (and other granulocytes) ready

for deployment on demand. Eosinophils have a life span of

a few days in circulating blood, although they can survive

longer in the tissues. They are commonly found in the con-

nective tissue of the digestive tract. Some of the granules

in eosinophils are highly toxic to parasitic worms such as

schistosomes. Eosinophils also play a role in moderating

inﬂ ammation resulting from an allergic reaction. They selec-

tively ingest and degrade antigen-antibody complexes and

also degrade histamine, therefore limiting inﬂ ammation.

D. Cui

Eosinophil

Neutrophil

Eosinophil

D. Cui

Neutrophil

Basophil

Neutrophil

Basophil

Figure 8-7B. Basophil, blood smear. Wright stain,

754; inset 1,569

Basophils are the least numerous in the blood circulation,

comprising less than 1% of the leukocytes. It is therefore

difﬁ cult to ﬁ nd them in normal blood smears. They have a

two- to three-lobed nucleus and large granules in the cyto-

plasm. These granules stain deep violet with Wright stain

and are distributed unevenly in the cytoplasm. Speciﬁ c gran-

ules in basophils contain heparin, histamine, peroxidase,

and eosinophil and neutrophil chemotactic factors (attracts

eosinophils and neutrophils to the site). Azurophilic gran-

ules are also present in basophils. Basophils have a similar

function to mast cells in connective tissue. They contrib-

ute to allergic reactions by releasing histamine and heparin

to produce inﬂ ammation at the allergic reaction site. (For

details, see Fig. 4-4B).

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Figure 8-8. Eosinophil in connective

tissue. EM, 12,000

The irregular surface contours of this cell

suggest that it was in motion at the time

the specimen was obtained. The two lobes

typical of the nucleus of an eosinophil are

present in the section, and the relatively

large speciﬁ c granules have the features

that are characteristic of eosinophilic gran-

ules. The proﬁ les of the granules have two-

dimensional shapes that are consistent with

a biconvex three-dimensional shape. Each

granule has a crystalline core (internum)

composed of a major basic protein, one

of the cationic proteins sequestered within

eosinophilic granules.

Internum (crystalloid)

in eosinophilic granules

Internum (crystalloid)

in eosinophilic granules

Lobes of nucleus

Types of

Leukocytes

Approximate %

of WBCs

Nucleus Granules in Cytoplasm Main Functions

Lymphocyte 25%–33% Round, relatively large

compared to cell size

If present, only a few azurophilic

granules

Play important role in

immune defense

Monocyte 3%–7% Large, kidney shaped

or horseshoe shaped;

nonsegmented

Azurophilic granules only (lysozyme,

endogenous pyrogens/IL-1)

Phagocytosis of any

recognizable nonself

agents after becoming

mature tissue phagocytes

Neutrophil 54%–62% Multilobed (ﬁ ve or

more);

segmented

Azurophilic (primary) granules contain

lysosome, myeloperoxidase, and

superoxide; small, salmon-pink, speciﬁ c

( secondary) granules contain major

basic proteins, lactoferrin, lysozyme,

collagenase, and proteases

Defend against bacterial

and fungal infection

Eosinophil 1%–3% two to three lobes;

segmented

Azurophilic granules; large red,

speciﬁ c granules contain major basic

proteins, acid phosphatase, peroxidase,

arylsulfatase, and β-glucuronidase

Defend against infection

by parasitic worms;

moderate inﬂ ammation

in allergic reaction; ﬁ ght

viral infection

Basophil <1% two to three lobes;

segmented

Azurophilic granules; large violet (or

purple-blue), speciﬁ c granules contain

histamine, heparin, peroxidase, eosino-

phil/neutrophil chemotactic factor

Involved with

inﬂ ammation and

allergic reactions (similar

to mast cells)

TABLE 8-1 Leukocytes

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