White Blood Cells
Morphology and Counts
• Produced predominately in the bone
• Capable of mitotic division up to the
• Responds to an increased demand
• Takes 3-5 days to influence peripheral
• Cells mature into metamyelocytes→ band
cells→ Segmented cells.
• 80% of granulocytes are found in the bone
marrow of healthy animals.
• These cells are released from bone
marrow with the oldest (segmented) to
increased peripheral need.
• In less than two days, the bone marrow
• Dogs have the largest storage pool (5
days) whereas bovines have limited
Functions of Leukocytes
• Characterized by the presence of
• Function of these cells occurs in the
tissues, not in the bloodstream.
• These cells do not recirculate
• Primary functions:
• Phagocytosis and killing of microbes.
• Usually circulate for 10 hours before
migrating into the tissues.
• Ingest material and eventual bacterial
• Inhibit chemical mediators such as
histamine and serotonin which are
released during allergic
• Have phagocytic and bacteriocidal
properties similar to neutrophils but not
• Have parasiticidal properties.
• Animals with heartworms may have hig
numbers of eosinophils.
• Secrete mediators of
associated with hypersensitivity
• This release occurs when
antigens complex with IgE is
located on the cellular surface.
• Differentiate into the cells of the
present in most tissues.
• Become macrophages once they
migrate into the tissues.
• Capable of multiplying within the
• Can survive for long periods of time
• Phagocytosis and digestion of particulate material,
bacteria, and dead cells.
• Macrophages are less responsive to bacterial
infections than neutrophils but are more effective
against fungal infections.
• Synthesis and release of substances invloved in
inflammation and immune response.
• Expressions of immune response by presenting
antigens to T-lymphocytes.
• Serve as a major source of colony stimulating
factors and cytokines involved in hemtopoiesis.
• Cause bone marrow to produce more
• Distributed in lymphoid tissue to
include lymph nodes, spleen,
thymus, tonsils, bone marrow, and
• Capable of division.
• Recirculate in the blood.
• B cells: turn into plasma cells
which secrete immunoglobulins.
Usually stayin the lymphoid
• T cells: transform into effector
cells that produce lymphokines
which function in mediation of
• Neutrophils: multiple nuclear lobules
separated by constrictions.
• Band granulocytes: band (horseshoe)
• Eosinophil: Lobulated nucleus and
cytoplasm containing reddish pink
• Basophil: Lobulated nucleus and purple-
blue (Basophilic) granules.
Neutrophil compartments in
• Marginated neutrophil pool: during any
moment of time, some neutrophils are
loosely adhered to the vessel wall. These
cells are not sampled when blood is drawn
from non-stressed animals.
• Circulating neutrophil pool: neutrophils
moving with RBC’s and fluid. Are sampled
pool of cells.
• When an animal is stressed- marginated
pool becomes circulating pool. Called
Response to Inflammation
• Inflammatory cells at sites of inflammation release
substances (cytokines, interleukins) into the blood
to attract neutrophils.
• Segmented neutrophils are released from the
mature storage compartment in the bone marrow.
• Increase in peripheral numbers (measurable in 2
• If sudden demand for neutrophils depletes the
storage compartment of segmented neutrophils,
then band cells are released.
• With continued depletion, cells in bone marrow
begin to divide.
• When source of inflammation is removed, demand
for neutrophils decrease, and production slows
Immature Neutrophils in
• Immature neutrophils in circulation (left shift)-
defined as the release of immature neutrophils
(usually bands) into the circulation to meet tissue
• The appearance of immature neutrophils is termed
• Regenerative left shift: the absolute number of
neutrophils in circulation is increased. The bone
marrow has increased the neutrophil release.
• Degenerative left shift: the nummber of
neutrophils has decreased. This is a poor
• Adult cattle have a relatively low absolute
number of neutrophils in circulation and
have a small marrow storage pool.
• A degenerative left shift is typical of the
acute inflammatory response in cattle.
Some terminology for morphology
• -penia: decreased number of cells in the blood
• -philia or –cytosis: increased number of cells in the
blood (neutrophilia, lymphocytosis).
• Left shift: increased numbers of immature
neutrophils in the blood.
• Leukemia: neoplastic cells in the blood or bone
• Leukemoid response: marked leukocytosis
(>50,000/ul) usually a result of inflammatory
• Lymphoproliferative disorders: conditions in
lymphocytes or plasma cells proliferate abnormally.
• Myeloproliferative disorders: a group of bone
marrow disorders, usually neoplastic, which stems
from on of the bone marrow cell lines.
• Not always due to infection.
• Stress leukogram: endogenous or exogenous
• Characterized by neutrophilia without a left
shift, monocytosis, lymphopenia, and
• Caused by a shift from the marginal to the
• Physiological luekocytosis: transiet condition
caused by excitement, epinephrine release and
• Neutrophilia without left shift and normal or
increased lymphocyte number.
• Occurs more commonly in the cat than the dog.
• Increased bone marrow proliferation, shift
from storage pool to blood.
• Mild inflammation yields a leukocyte
response similar to stress.
• Purulent reaction: neutrophils with a left
• Intense response with left shift
• Can confuse immature cells of myeloid
series with neoplasia (leukemia)
• Degenerative shift usually is due to
extreme migration of cells into tissues
and/or detrimental side effects of toxins.
• Characterized by ctyoplasm basophilia,
Dohle bodies, toxic granulation, and/or
• Cells have decreased functional abilities.
• Animal with toxic, degenerative shift may
be compromised by lack of adequate cell
number and decrease ability of cells to
• Blue cytoplasmic inclusions.
• Low numbers may be found in healthy
• Indicates toxicity in other species.
• Neutrophils with five or more nuclear
• Normal aging change of neutrophils which
normally occurs in the tissues, not
• May occur with excessive levels of
corticosteroids from administration or
• Chronic inflammation.
• Artifactual change in the blood that sits for
a period of time.
• Hyposegemented neutrophils that function
• Hereditary disorder; failure of the nucleus
in mature cells to undergo segmentation.
• Physiologic: due to epinephrine release.
• Common in chronic inflammation and
chronic antigenic stimulation.
• Later stages of resolving infections.
• Neoplastic lymphocytosis such as
leukemia and lymphosarcoma
• Common finding on CBC
• Associated with stress
• Immunosuppressive therapy
• Immunodeficiency syndrome
• Viral infections such as parvo.
• Characteristic changes in the morphology of
lymphocyte that has been stimulated to
produce antibody (B cells) or lymphokines (T
• Morphological changes: increased cytoplasm,
increased basophilia of cytoplasm, increased
aggregation of chromatin, and may lack
perinuclear clear zone.