140
UNIT 2
Basic Tissues
Leukocytes: Agranulocytes
CLINICAL CORRELATION
Figure 8-4C.
Chronic Lymphocytic Leukemia, Blood
Smear.
Wright stain,
3
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
inF 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 speciF
c
for CLL, are commonly seen on peripheral blood smears.
CLL
lymphocytes
Smudge cell
Smudge cell
Neutrophil
C
Figure 8-4A.
Lymphocytes, blood smear.
Wright stain,
3
754;
inset
3
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 classiF 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
A
D. Cui
Lymphocyte
Neutrophil
Monocyte
Monocyte
B
Figure 8-4B.
Monocytes, blood smear.
Wright stain,
3
754;
inset
3
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 nonspeciF c granules present in the cyto-
plasm of both agranular and granular leukocytes. They are distinct
from the speciF 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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