Hem 4 - Leukocytes

Question 1

what are the two major classes of WBC broken into

Answer 1

granulocyte, mononuclear cells

Question 2

where do WBC go after they leave the bloodsteam

Answer 2

WBC are transported to sites of infection/injury where
they leave the bloodstream and perform immune and
defense functions against pathogens and tissue damage

Question 3

lifespan of WBC and how often they need to be replenished

Answer 3

Although numbers are much lower than RBC (1/1000th as
many), they have a much shorter lifespan in circulation and
need to be continuously replenished.

Question 4

what do changes in WBC numbers, type and morphology reflect

Answer 4

Changes in WBC numbers, morphology and cell types within
blood reflect systemic changes (eg. infection) - the distribution
of the various WBC types often reflects the nature and
severity of those stressors (bacterial, viral, parasitic)

Question 5

evaluation of the leukon - what to look at to count and characterize cells in blood

Answer 5

Count and Characterize the cells in blood (normally done
as part of the CBC):
* Total WBC count (per μl or ml of blood)
* Differential WBC count (% of WBC of each type)
* Blood smear (morphology of WBCs)

Question 6

what is:

Leukocytosis, Leukopenia, and Pathological vs Physiological

Answer 6

Leukocytosis: Increase in the total number of WBCs.

Leukopenia: Decrease in the total number of WBCs.
In either case the task is then to determine whether the
change is:
* Pathological: Processes such as infection, inflammation
tissue damage, cancer or other underlying disease alter
WBC numbers and distribution.
* Physiological: Hormones such as cortisol, epinepherine
can also alter WBC numbers and distribution.

To make these determinations, we first need to understand
the biology of the different cell types.

Question 7

circulating WBC - branches and types within the branches

Answer 7

granulocytes, agranulocytes

granulocytes = neutrophils (65-75%), eosinophils (2-5%), basophils

agranulocytes = lymphocytes (20-25%), monocytes (3-8%)

Question 8

Neutrophils - what type of cells are these, what do they do, circulation pattern, what are the granules responsible for and their names

Answer 8

Major phagocytic cells in the innate immune response

• “First responders” at sites of infection, tissue damage.
• Continually circulating- binding and releasing from
  vascular endothelia
• Granules in the cytoplasm responsible for killing
  microbes
• Primary granules
• Secondary granules

Question 9

intramedullary phase: neutrophols and their precursors in bone marrow (pools and what is in this)

Answer 9

pool 1 = proliferative/mitotic pool = myeloblasts, promyelocytes, myelocytes

pool 2 = maturation pool = metamyelanocytes, band cells

pool 3 = storage or reservation pool = band cells, mature neutrophils

Question 10

intravascular phase: neutrophils in circulation (pools and what is happening with them, normal lifespan, what affects the lifespan)

Answer 10

circulating pool = neutrophils in circulation

marginal pool = neutrophils marginated along capillary

Normal neutrophil lifespan in the bloodstream (both pools) is
less than 24 hours.
* This can be dramatically decreased by infection etc. when the
transit time becomes much shorter.

Question 11

tissue phase: neutrophils leave circulation and enter tissue

Answer 11

Normally neutrophils enter the tissues by diapedesis
through the intercellular junctions of vascular endothelium.

• Stimulated by chemotactic factors secreted by bacteria,
  other WBC, damaged cells in tissue.
• This is a one-way process – once in tissues, neutrophils
  perform their functions and ultimately die after 24 – 48 h.
• Neutrophil migration to the tissues depends on severity
  and duration of tissue injury.
• Neutrophil influx into tissue is maintained by new cells
  entering blood from bone marrow.

Question 12

what is the order of events for a neutrophil to go from ciruculation to do its job in tissue

Answer 12

pavementing, emigration, chemotaxis , phagocytosis

Question 13

will you ever see recirculation of neutrophils that have emirgrated

Answer 13

never, it is a one way street

Question 14

examples of what happens when neutrophils accumulate in large numbers at tissue sites

Answer 14

pyothorax, pyometra

Question 15

steps in neutrophil responses to pathogens (phagocytosis)

Answer 15

1. Bacterium becomes attached
   to membrane evaginations
   called psueudopodia
2. Bacterium ingested in the
   phagosome
3. Phagosome fuses with
   lysosome
4. Lysosomal enzymes
   digest captured material
5. Digestion products are
   released from the cells

Question 16

immaure neutrophils in circulation: band cells/band neutrophils – what do they look like, what is an increased amount called and what does it indicate, what other conditions can cause it

Answer 16

Band cells or band neutrophils have
unsegmented nuclei and is the stage immediately preceding the mature neutrophils

An increased proportion of bands in the peripheral blood is often referred to as a ‘left shift’, and may indicate the presence of infection.

Other conditions, such as hypoxia
and shock, can also cause a left shift

Question 17

changes in blood neutrophil counts can be caused by changes in one or more of the following what?

Answer 17

1. The rate of neutrophil production (granulopoiesis)
2. The extent of neutrophil influx from the marrow pool to the
   blood
3. A shift of neutrophils between the circulating and marginal
   pools
4. The intravascular life span of neutrophils
5. The rate of efflux from the blood to tissue

Question 18

what are the responses to infection and inflammation and what happens during them?

Answer 18

Initial Response: Decrease in circulating neutrophil numbers due to increase margination and migration into the tissues

Intermediate Phase: Neutrophils from the marrow reserve are released into the vasculature causing an increase in neutrophil numbers

Progressive Phase: As the inflammation progresses, both marginal and circulating pools increase due to increased granulopoiesis and release of newly formed cells into the vasculature.

Question 19

neutropenia - what is it characterized by, what is the classification of it, what % do they make up

Answer 19

Characterized by an abnormally low number of neutrophils

• Neutrophils usually make up 50-70% of circulating white
  blood cells and serve as the primary defence against infections by destroying bacteria in the blood
• Neutropenia can be acute or chronic depending on the duration of the illness

Question 20

what causes a decrease in neutrophil numbers?

Answer 20

Increased efflux to tissues (early phases of infection)

• Decreased granulopoiesis or release from the marrow
  (leukemia, myelofibrosis, chemotherapy)
• Decreased cell survival in vascular compartment

Question 21

are there differences in appearance of neutrophils in species

Answer 21

yes

Question 22

toxic changes in neutrophils - what happens with development, term for the change, what are toxic changes, what do they look like

Answer 22

When neutrophils develop and mature at an accelerated rate in
the presence of significant infection or tissue damage, their
appearance is altered by the presence of TOXIC CHANGES.

• These are morphologic abnormalities acquired during
  maturation under conditions that intensely stimulate neutrophil
  production and shorten the maturation time in marrow.
• Most of the toxic changes reflect accelerated granulopoiesis
  and release from the marrow – incomplete chromatin
  condensation and ribosomal proteins remaining in cytoplasm (in
  many ways analogous to reticulocytes when RBC maturation
  and release is accelerated in response to anemia).
• Usually (but not always) the changes are observed in band
  cells, as these are quickly released into circulation in times of
  increased demand (left shift).

Question 23

apperance of toxic change in the three sections

Answer 23

1. Normal segmented (A) and late
   band neutrophils (C), have white
   cytoplasm with pink granules,
   long and fairly narrow nuclei and
   tightly condensed chromatin.
2. Segmented (B) and band
   neutrophils (D) with toxic change
   have less condensed chromatin
   than their normal counterparts
   and bluer cytoplasm due to
   retention of ribosomal RNA.
3. Doehle body (ribosomal protein
   aggregate – arrow) in Band Cells
   is considered toxic change (E)

Question 24

stress leukograms - what happens when animals are stressed, why does it happen, what is it accompanied by, what induces it

Answer 24

Often in cases where an animal is stressed by exercise or
the act of restraint/blood collection, the numbers of mature
neutrophils increases in the blood. (Neutrophilia without a
left shift).

• This is due to mobilization of the “marginated” pool of
  neutrophils in the blood vessels – there is no increase in the
  band cells present and no toxic changes.
• It is usually accompanied by a decrease in the numbers of
  lymphocytes and an increase in the numbers of monocytes.
• It is thought to be induced by cortisol and epinepherine and
  is considered to be a normal or non-specific change in many
  cases

Question 25

life cycle of monocytes and macrophages - circulation and %, why does a monocyte convert, what are monocytes attracted to, can macrophages divide and how do they adapt

Answer 25

Monocytes circulate in the bloodstream and represent ~5% of
WBC numbers. Like neutrophils, they are ultimately destined to
leave the blood and enter tissue to act as resident immune cells
or in response to infections or tissue damage.

• When a monocyte enters damaged tissue through the
  endothelium of a blood vessel, it undergoes a series of changes
  to become a macrophage
• Monocytes are attracted to a damaged site by chemical
  substances (cytokines, chemokines) through chemotaxis
• Macrophages are unable to divide, they perform differentiated
  functions related to pathogen clearance and removal of dead
  cells and debris

Question 26

macrophage life cycle - attraction process, how long is the life span, when do they fuse

Answer 26

The stimuli that attract monocytes include damaged cells, pathogens, histamine released by mast cells and basophils, and cytokines released by macrophages already at the site

• Unlike short-lived neutrophils, the life span of a macrophage ranges from months to years
• Sometimes macrophages fuse to form giant cells, commonly seen in tuberculosis and other granulomatous diseseases (Actinobacillus, Actinomyces)

Question 27

functions of macrophages - (5) and components involved

Answer 27

Phagocytosis (essentially like neutrophils) and Microbicidal Activity

• Scavenger Role – Cellular remnants, apoptotic cells, lipids, etc.
• Regulation of immune response (“presents” antigens to lymphocytes to activate the immune response).
• Cytotoxicity – Direct killing of tumor and infected cells (perforins etc.) (Degranulation)
• Secretory Role – cytokines, granule contents, clotting factors (Degranulation).

Question 28

resident macrophages in tissues - where are alveolar macrophages, microglia, kuffer cells, histiocytes and osteoclasts located

Answer 28

lungs
brain
liver
connective tissue
bone

Question 29

eosinophils - % present, primary role, other tasks they have been associated with

Answer 29

Comprise 1-4% of total WBC numbers.

• Primarily appear responsible for combating parasitic infection in the body
• They have also been widely implicated in allergy and asthma as their granules, when released, cause some of the associated respiratory and skin signs (edema, itching, congestion)

Question 30

eosinophil granules - two branches and then if they have subsets within

Answer 30

histamine and proteins

proteins include: major basic protein, RNAse, DNAse, plasminogen, lipase

Question 31

functions of eosinophils - two categories and details within

Answer 31

Phagocytosis and Bactericidal Activity
* Eosinophils can phagocytose wide variety of substances,
including bacteria, yeast, antibody coated RBCs, mycoplasma
and mast cell granules

• Eosinophils are less efficient in phagocytosis and killing of
  bacteria compared to neutrophils
  Parasiticidal Activity

PARASITICIDAL ACTIVITY
* Direct phagocytosis of parasites by eosinophils is not involved,
instead, eosinophils release granule contents when in contact with the antibody coated (opsonized) parasites. Kill by oxidation of parasite membranes.

• Protective antiparasitic immunity by esoniophils has been observed against numerous different parasites

Question 32

eosinophelia - when is it seen, how is it occasionally observed

Answer 32

Typically seen in cases with a parasitic infestations

• Also found in some cases of rheumatoid arthritis, extensive
  skin diseases, and with the use of certain drugs such as
  penicillin.
• Occasionally observed as an idiopathic infiltrate in muscle
  (eosinophilic myositis) or lung (pulmonary infiltrate with
  eosinophils)

Question 33

eosinopenia - what is it, when does it occur, reason for drop in numbers, what is it also a feature of

Answer 33

Eosinopenia is a decrease in eosinophil number.

• Occurs when glucocorticoids are administered or rise endogenously (Cushing’s, Stress)
• The reason for drop in numbers is a redistribution of eosininophils into capillary beds with longer term
  decreases in production
• Eosinopenia is also a feature of hyperadrenocorticism because of increased endogenous corticosteroid concentration

Question 34

basophils - how common, what do they store, recruitment

Answer 34

Basophils are the least common of the granulocytes, representing about 0.5% to 1% of circulating leukocytes. Specific roles not well understood.

• Store histamine, which causes some of the symptoms of an
  allergic/anapylactic reaction. Similar in many ways to Mast Cells in tissue.
• Like all circulating granulocytes, basophils can be recruited out of the blood into a tissue when needed

Question 35

functions of basophils - what role do they play, what are the granules rich in, what do they recruit to inflammed sites

Answer 35

• Basophils play a role in immune mediated inflammation,
  especially in analphylaxis and cutaneous hypersensitivity
• Granules of basophils are rich in histamine, heparin, sertonin and hyaluronic acid
• Basophils produce eosinophilic chemotactic factor that attract eosinophils and neutrophils to inflammed sites

Question 36

basophilia - how common, associated with what, what is it also associated with in dogs, why is basopenia not recognized

Answer 36

Increase in basophil numbers are rarely numerically dramatic

• Basophilia is associated with the diseases causing increased IgE production
• In dogs, basophilia is commonly associated with heartworm infestation
• “Basopenia” is not recognized because normal numbers are so low that absence on a CBC is not
  notable