Encyclopedia of Health and Medicine

148 The Blood and Lymph
MYELOMA; SIGNS AND SYMPTOMS OF CANCER; SMOKING
AND HEALTH; STAGING AND GRADING OF CANCER.
leukocyte A white BLOOD cell, also referred to as
a WBC. Leukocytes are the foundation of the
body’s IMMUNE RESPONSE and are phagocytic—that
is, they have the ability to consume other cells.
They circulate in the blood and the LYMPH as well
as reside in tissues throughout the body. There are
three basic types of leukocytes: granulocytes,
monocytes, and lymphocytes. Each type has several
subtypes. The SPLEEN and lymph tissues produce
monocytes and lymphocytes; the red BONE
MARROW produces granulocytes.
HEALTH CONDITIONS THAT AFFECT
LEUKOCYTE COUNTS
ALLERGY response
ASTHMA
AUTOIMMUNE DISORDERS
CHEMOTHERAPY
environmental toxin exposure HYPERSENSITIVITY REACTION
INFECTION
INFLAMMATION
LEUKEMIA
LEUKOPENIA
LYMPHOCYTOPENIA
LYMPHOMA
many cancers
medication side effects
MONONUCLEOSIS, INFECTIOUS
RADIATION THERAPY
surgery
vitamin B 12 deficiency
A healthy adult has between 5,000 and 10,000
leukocytes per microliter of blood, with granulocytes
accounting for about 70 percent. Increases in
certain subtypes of leukocytes suggest particular
health conditions. A substantial increase overall in
LEUKOCYTE count may indicate a cancer of the bone
marrow such as LEUKEMIA or LYMPHOMA. The ratio
between erythrocytes (red blood cells) and leukocytes
in the blood is also an important diagnostic
indicator.
For further discussion of leukocytes within the
context of blood and lymph structure and function
please see the overview section “The Blood
and Lymph.”
See also B-CELL LYMPHOCYTE; CELL STRUCTURE AND
FUNCTION; ERYTHROCYTE; HEMATOPOIESIS; PHAGOCYTO-
SIS; PLASMA; PLATELET; SIDE EFFECT; THYMUS.
leukopenia A decline in the number of leukocytes
(white BLOOD cells) circulating in the blood
to fewer than 4,000 leukocytes per microliter of
whole blood. The most common manifestation of
leukopenia is NEUTROPENIA, a shortage of granulocytes
called neutrophils. Most leukopenia is secondary
to other health conditions a person may
have, such as viral infections or cancers that
involve the BONE MARROW, and circumstances, such
as CHEMOTHERAPY. Numerous medications can
cause leukopenia as an undesired SIDE EFFECT of
treatment. In such situations the doctor will evaluate
the relative value of the inherent risks in
continuing or discontinuing the causative medication.
Leukopenia lowers the body’s ability to resist
and fight INFECTION and when severe can allow
life-threatening infections to invade. Frequent or
unusual infections, especially persistent GINGIVITIS
or periodontitis, may suggest leukopenia. Treatment
targets any infection or other underlying
cause.
See also LYMPHOCYTOPENIA; PERIODONTAL DISEASE;
THROMBOCYTOPENIA.
LEUKOCYTES
Type of Leukocyte Subtypes Organ that Produces
granulocytes basophils, eosinophils, neutrophils red BONE MARROW
monocytes macrophages (reside in the tissues) SPLEEN, lymph nodes
lymphocytes T-cell lymphocytes SPLEEN, lymph nodes, THYMUS
cytotoxic T-cells
helper T-cells
memory T-cells
suppressor T-cells
B-cell lymphocytes
memory B-cells
PLASMA cells