(W1) Leukocyte Disorders Flashcards
Describe the morphology of leucocytes (neutrophil, lymphocyte, monocyte, eosinophil and basophil)
Neutrophil:
- lobulated nucleus
- grey-pink cytoplasm
Lymphocyte:
- round nucleus
- small amount of pale blue cytoplasm
- smaller than a neutrophil (in diameter)
Granular lymphocyte:
- dark red/magenta cytoplasmic granules
- present in the dog (and occasionally in cats and horses)
- (mainly cytotoxic T lymphocytes, less so B cells)
Monocyte:
- equal to or larger than neutrophil
- lobulated nucleus (not as lobulated as neutrophil)
- thick nucleus
- blue cytoplasm
- some have vacuolated cytoplasm
Eosinophil:
- many orange granules in cytoplasm
- (granules in greyhounds/sight hounds don’t stain very well)
Basophil:
- purple granules in cytoplasm
Lymphoid stem cell gives rise to what cells?
- B lymphocytes
- T lymphocytes
- NK lymphocytes (natural killer)
What are platelets derived from?
megakaryocytes - fragments of megakaryocytes form platelets
Myeloid stem cells give rise to what cells?
- erythrocytes
- neutrophils
- monocytes
- eosinophils
- basophils
- mast cells
Note and mast cells are different cells*
- They appear similar morphologically, but are coming from distinct
progenitor cells
- basophils circulate in the blood
- mast cells are only found in tissues in health
What are the last 3 stages of neutrophil maturation?
- metamyelocyte
- band
- segmenter (aka mature neutrophil)
will see these stages in blood film
Describe the neutrophil distribution in the bone marrow
There are 2 compartments:
- the neutrophil proliferation compartment (containing the early stage cells, apart form the last 3 stages, of neutrophil development)
- the neutrophil maturation and storage compartment (containing the metamyelocytes, band neutrophils and mature/segmented neutrophils
Describe the neutrophil release from bone marrow
- mature/segmented neutrophils are released first
- during increased tissue
demand for neutrophils, mature neutrophils are exhausted so band neutrophils and
metamyelocytes may be
released in the blood
circulation prematurely (this is called LEFT SHIFT)
What are the morphologies of the last 3 stages of neutrophil maturation?
Metamyelocyte - kidney shaped nucleus
Band neutrophil - c-shaped (or u-shaped) nucleus that isn’t lobulated
Mature (segmented) neutrophil - lobulated nucleus (up to 5 lobes)
What are the 2 neutrophil pool in the blood circulation? What are the proportions of neutrophils found in each pool in mammals generally (any exceptions?)?
Circulating Neutrophil Pool (CNP):
- neutrophils that are free flowing in the blood
Marginated Neutrophil Pool (MNP):
- neutrophils (rolling neutrophils) that temporarily adhere to the endothelial cells of blood vessel walls
- after adhesion, these neutrophils may return to the circulating pool, or migrate to the tissues
Proportions:
- most mammals: 1/2 of blood neutrophils found in MNP and other half in CNP
- cats: 3/4 in MNP and 1/4 in CNP
How are neutrophils attached to the endothelial cells of blood vessels?
attachment of neutrophils is mediated by adhesion proteins found on the surface of neutrophils and on the surface of endothelial cells
How long do neutrophils survive for and how are effete neutrophils removed?
in health, they survive in the tissues for 24 to 48 hours
effete neutrophils are largely removed by macrophages (phagocytosed by macrophages) of the spleen, liver, bone marrow, and other tissues
Describe the neutrophil attachment to endothelial cells (the rolling)
- neutrophils found in the blood vessels are circulating with the blood flow
- they have certain molecules on their surface and these attach to receptors on the surface of endothelial receptors
- they then start rolling until they find a way they can exit
- they normally exit between epithelial cells, or at times, through the endothelial cell itself where they enter tissues
In relation to blood samples, what pool are the neutrophils from?
the sample only contains neutrophils part of the CNP
in an animal where there is movement from the CNP to the MNP, numbers will appear lower than the normal (and vice versa)
What is neutrophilia?
elevation of neutrophil absolute count
What is physiologic (shift) neutrophilia and what causes it? Is it seen in health and how long do leucocyte numbers take to return to normal levels?
a shift of neutrophils from the MNP to the CNP
Cause:
- results from effects of catecholamines (typically associated with fear, excitement, and exercise)
- shift may be caused by the change in fluid dynamics that results from increased blood flow rate, especially in lungs
this is seen in most healthy animals and leukocyte numbers increase quickly/return to normal fairly fast after stimulus disappear
What is the magnitude of neutrophilia in physiologic (shift) neutrophilia?
magnitude may be up to 2x x the upper limit of normal for canine, equine and bovine blood
3-4x the upper limit for a cat (because of cat’s larger MNP)
What is steroid (stress) neutrophilia a result of? How does it vary (or not) between species?
results from changes created by the effects of endogenous or exogenous glucocorticoids on neutrophil kinetics
Glucocorticoid effects on blood leucocyte counts differ amongst various animal species
What causes neutrophilia in a stress leucogram? Can this indicate pathology?
- Neutrophils shift from the MNP to the CNP because the production of adhesion molecules is down-regulated
- Fewer neutrophils emigrate to tissues, and thus neutrophils have an increased circulating life span
- Increased release of neutrophils from the bone marrow (segmented neutrophils mostly)
animal might have hyperadrenocorticism/Cushing’s Disease
In which species is the steroid (stress) leucogram most frequently seen in and what are its characteristics?
mostly seen in dogs
Mature:
- neutrophilia
- lymphopenia
- eosinophilia
- monocytosis
the combination of mature neutrophilia (↑ segmented neutrophil numbers) and
lymphopenia (↓ lymphocyte numbers) are the most frequent findings in a stress
leucogram
What are the 2 ways leucocytes are assessed in clinical practice?
Leucocyte numbers:
- manual methods
- haematology analyser
Leucocyte morphology:
- microscopic examination of blood smear
What is a manual method (excluding differential cell count) to assess leucocyte numbers?
Haemocytometer method:
- dilute blood (add solution), which causes RBCs to rupture (want RBCs to rupture so only have WBCs in the sample to look at)
- the blood, after diluted, is dispensed into haemocytometer chambers
method is labour-intensive and so not routinely done
How do haematology analysers work?
Most analysers are either using impedance technology, or laser technology (flow cytometry)
Impendence Technology:
- After addition of lysing agent to remove erythrocytes, each leucocyte cell passes through an aperture creating a voltage peak
- the height of the peak corresponds primarily to the volume of the cell
Laser Technology:
- Cells are suspended in a diluent and injected into a special flowing fluid
- Cells in the sample stream pass through a laser beam, mostly one at a time
- each cells scatters the light in different directions, depending on the cell’s size and contents
- Sensors detect the scattered light at various locations
- Computer programs
analyse the data from the sensors to determine which cell has passed through the laser beam
What is the purpose of differential leucocyte count?
determine the percentage of each of the while cell types (neutrophils, lymphocytes, monocytes, eosinophils, basophils)
Describe how to perform the manual leucocyte differential count (using a differential cell counter)
performed on a blood smear using the microscope and a cell counter
1) Prepare the blood film and find the monolayer (so that cell aren’t on top of each other and can see enough cytological detail - where you can assess cell morphology)
2) Using the 100x objective, move across the monolayer of the smear as shown
3) Press the cell counter button corresponding to the leucocyte/s present within
each field of view
4) The counter will make a noise to notify you that 100 cells have been counted
5) The percentage of each white cell type can be seen on the cell counter’s screen
What are the advantages and disadvantages of performing a manual differential leucocyte count?
Advantages:
- able to simultaneously assess for other possible abnormalities
- e.g. toxic
changes of neutrophils, neoplastic cells in blood, erythrocyte shape abnormalities, presence of
infectious organisms, etc - these can’t be detected with a haematology analyser
Disadvantages:
- only considered an estimate
This is due to:
- sampling error: i.e. only 100 cells counted usually, are they representative?
- identification error: operator variability, difficult to assess cells in samples of low quality and sometimes with diseases causing alterations of cell morphology
What are disadvantages of automated method of differential cell count (haematology analyser)?
- accuracy of results is highly variable between different analysers
- Can be problematic in diseases causing alterations of blood cell morphology (may misidentify cells)
What are heterophils and in what species are they found in?
granulocytic cells, equivalent to neutrophils
found in the blood of various animal species (e.g. avian, reptiles, fish, guinea pigs, rabbits, manatees, etc.)
In which species do neutrophils predominate over lymphocytes and what are the ratios in these species?
dogs and cats
Neu:Lym
dogs - 1.1 - 3.5
cats - 1.8
In what species are the neutrophils and lymphocytes the same in proportion (what is the ratio?
horse
1.1
In what species do the lymphocytes predominate over the neutrophils (what is the ratio)?
cattle - adult ruminants and many species of birds
0.5
Which species has a less pronounced WBC response to inflammation?
horses and cattle (compared to carnivores)
??paradoxically, modest increase in horses and cattle are more significant??
What are the causes of neutrophilia?
Physiological, Non-Inflammatory:
- Epinephrine (adrenaline) effect (neutrophils shift from marginated pool → circulating pool)
- Glucocorticoid effect (↑ endogenous or ↑ exogenous glucocorticoids)
→ Neutrophil shift from marginated to circulating pool
→ Increased production/release from maturation pool of BM
→ Decreased transmigration to tissues
Inflammatory Response:
- infection (local/systemic)
- tissue necrosis/injury
- immune-mediated diseases
- tumour, myeloproliferative disorders
similar mechanisms (inflammatory and physiological) can cause heterophilia
What are the causes of neutropenia (decreased absolute count for neutrophils)?
Acute, overwhelming inflammation (AOI):
- endotoxaemia (endotoxin released into blood) caused by infection with gram -ve bacteria (neutrophils shift from circulating pool →
marginated pool)
- AOI seen in cows with mastitis caused by gram -ve bacteria
- Margination in vessels or emigration to tissues»_space;> neutrophil release from BM
Peripheral destruction neutropenia (e.g. immune-mediated destruction)
Neutropenia due to decreased bone marrow production (e.g. granulocytic hypoplasia)
- Frequently seen in animals receiving chemotherapy for cancer (cytotoxicity to rapidly-dividing cells)
- also idiopathic
- others
What do reactive lymphocytes look like (compared to normal) and when they encountered/present?
larger, more basophilic than normal lymphocytes
occasionally encountered in low numbers in blood during periods of antigenic stimulation
Where does lymphopoiesis occur and what does it depend on?
occurs in lymphoid tissues
- depends on n the degree and type of antigenic
stimulation, as well as an array of interleukin and cytokine influences
How long do lymphocytes survive for?
most are short-lived - 2 weeks
other lymphocytes (e.g. memory cells) may have intermitotic intervals of weeks months or years
Why are lymphocytes unique?
because they recirculate (blood, lymph, lymphoid
organs)
i.e. recirculate between blood and tissues
Describe the lymphocyte kinetics (movement) within the body
- blood lymphocytes are distributed between marginal and circulating pools
- they might enter lymphoid organs or nonlymphoid tissues
- those that enter nonlymphoid tissue may remain or enter the afferent lymphatic vessels and be transported to regional lymph nodes (and then perhaps to blood via thoracic duct
You are unlikely to see a reactive lymphocyte in a cat after vaccination, true or false?
False - you frequently see reactive lymphocytes after vaccination of a cat (few days to weeks after)
- because lymphocyte has been antigenically stimulated
What is the morphology of reactive lymphocytes?
- round nucleus remains
- but dark blue cytoplasm (instead of pale blue)
What is lymphocytosis and what are its causes?
increased absolute count for lymphocytes
Physiologic Response:
- shifting from MLP to CLP (young animals, especially cats and birds - epinephrine response)
Chronic antigenic stimulation:
- bacterial infection
- Rickettsial infection
- Viral infection
- Deep mycosis
- Protozoal infections
Post-vaccination
Hypoadrenocorticism
Lymphoid neoplasia:
- lymphoma/lymphoid leukaemia
- thymoma
What is lymphopenia and what are its causes?
decreased absolute count for lymphocytes
Causes:
Increased Endogenous/Exogenous Corticosteroids:**
- e.g. stress, hyperadrenocorticism, etc
Acute systemic infection:**
- septicaemia
- endotoxaemia
- viruses (often only in very early stages)
Immunosuppressive/chemotherapeutic drugs
Loss of lymphocyte-rich lymph (e.g. chylothorax)
Protein-losing enteropathy/Lymphangiectasia
Hereditary disorders
Once in tissues, monocytes differentiate into what?
cells of the mononuclear-phagocyte-system (MPS):
- macrophages (including Kupffer cells)
- alveolar macrophages
- type A synoviocytes
- microglial cells
- dendritic cells
What are resting macrophages called?
histocytes (or fixed macrophage)
What type of cells are dendritic cells?
antigen-presenting cells (APCs)
Is there a storage pool for monocytes?
no
there is no marrow storage pool (contrasts with neutrophils)
BUT evidence for marginated monocyte pool exists
What are some differences between macrophages and monocyte?
macrophages are derived from blood monocytes:
- macrophages NOT found in blood (only found in tissues
- monocytes seen in blood AND tissues
monocytes in tissues aren’t vacuolated BUT macrophages are vacuolated
monocytes have less cytoplasm BUT macrophages have more cytoplasm
How long do resident tissue macrophages survive for?
weeks to months
- are capable of division, and are functional phagocytes
What is monocytosis and what are its causes?
increased absolute count for monocytes
Causes:
- inflammation; acute and chronic (monocytosis reflects a need for macrophages in diseased tissue)
- granulomatous inflammation
- increased glucocorticoid levels particularly in dogs
- monocytic, myelo-monocytic leukaemia (rare)
What is monocytopaenia?
decreased absolute count for monocytes
not clinically significant feature
Eosinophil production and maturation in bone marrow parallels that of the neutrophils, true or false?
True
Describe the distribution of eosinophils and how long they stay in these areas
there are eosinophil storage pools
- marginal pool exists
- marginated and circulating blood eosinophils remain
in blood from minutes to hours and die in tissues - the duration in tissues not established but may be weeks or longer
What are some general functions of eosinophils?
ESSENTIAL to allergic responses and defence against parasites
- phagocytic and bactericidal properties
- inactivate mediators from mast cells
- attack larval and adult stages of a few parasites
What is eosinophilia and what are its causes?
increased absolute count for eosinophils
Causes:
- hypersensitivity reactions*
- parasitic infections*
Others:
- Mast cell degranulation caused by inflammations (inflammation in mast cell-rich tissues, e.g. skin,
respiratory, gastrointestinal)
- Paraneoplastic eosinophilia (e.g. mast cell tumours, T-cell lymphoma)
- Hypereosinophilic syndrome (idiopathic)
What is eosinopenia and what are its causes?
decreased absolute count for eosinophils
- increased glucocorticoid levels (e.g. stress)
- acute inflammation/infection
How do horse eosinophils differ from other species?
the eosinophilic cytoplasmic granules are more prominent in horses
What do basophil granules contain?
- histamine
- heparin
- sulphated mucopolysaccharides
Maturation of basophils parallels with that of neutrophils, true or false?
True
What are the similarities between basophils and mast cells?
they share many properties and serve similar functions
- both release histamine and participate in immediate and delayed hypersensitivity
reactions (amongst other functions)
note they share similar properties BUT are of a DISTINCT CELL LINE!!
Are mast cells blood or tissue leucocytes and so are they found in the blood in health?
tissue leucocytes
- therefore not found in the blood of normal healthy mammals
What is basophilia and what are its causes?
increased absolute count for basophils
Causes:
- allergic (hypersensitivity) reactions
- parasitism (e.g. fleas, GI nematodes)
- neoplasia
What is basopenia and why can’t it be documented?
decreased absolute count for basophils
Can’t be documented as basophil concentrations are typically very low in domestic mammals
What are the common leucogram changes in an epinephrine-mediated response? What are some examples where this response would occur?
- Mild neutrophilia/heterophilia (no left shift)
- Lymphocytosis (may be more significant in some species, e.g. cats, birds)
- Monocyte, eosinophil and basophil counts usually within the reference interval
Example:
- A young healthy animal which has experienced fear or excitement (lymphocytosis is a common finding in puppies)
- Blood sample taken shortly after seizuring activity, or strenuous exercise
What are common leucogram changes in a corticosteroid-induced response?
- Neutrophilia/heterophilia (usually without a left shift)
- Lymphopenia
- Eosinopenia
- Monocytosis in the dog and occasionally in the cat
What are common leucogram changes in inflammation/infection?
- Neutrophilia/heterophilia of various severity (a left shift may be present)
- Lymphopenia and eosinopenia may (or may not) be present (endogenous release of cortisol may contribute to these changes)
- Monocytosis may be present (some forms of inflammation e.g. granulomatous inflammation
are commonly associated with monocytosis)
What are leucocyte (WBC, segmented, band, lymphocytes) responses to epinephrine?
WBC - increase
Segmented neutrophils - increase
Band neutrophils - N/A
Lymphocytes - increase in cats
What are leucocyte (WBC, segmented, band, lymphocytes) responses to glucocorticoids?
WBC - increase
Segmented neutrophils - increase
Band neutrophils - N/A
Lymphocytes - decrease
note glucocorticoids can cause eosinopenia in all species and monocytosis in dogs
What are leucocyte (WBC, segmented, band, lymphocytes) responses to acute inflammation?
WBC - increase
Segmented neutrophils - increase
Band neutrophils - increase
Lymphocytes - variable
What are leucocyte (WBC, segmented, band, lymphocytes) responses to chronic inflammation?
WBC - variable
Segmented neutrophils - variable
Band neutrophils - variable
Lymphocytes - variable
note chronic inflammation causes monocytosis
What are leucocyte (WBC. segmented, band, lymphocytes) responses to overwhelming inflammation
WBC - decrease
Segmented neutrophils - decrease
Band neutrophils - variable
Lymphocytes - variable
What is left shift and what are the 2 types?
refers to the presence of immature neutrophil stages in the peripheral blood in increased numbers
Regenerative left shift - the absolute numbers of mature/segmented neutrophils are higher than the absolute numbers of immature neutrophils
Degenerative left shift - the absolute numbers of band or
immature neutrophils are greater than the absolute numbers of mature/segmented neutrophils (more common in cattle)
note a degenerative left shift is a poor prognostic indicator especially when combined with leucopoenia!!
(it means that BM is severely overwhelmed by inflammation - commonly seen in infection)
What causes a left shift to occur?
release of bone marrow stores (usually in response to acute inflammation)
- when the BM reserve of mature neutrophils is low or depleted
What is a toxic change of neutrophils and when do they occur?
refers to certain certain morphological abnormalities seen in neutrophils
- occur in the bone marrow prior to release
- they represent neutrophil maturation defects which occur during rapid neutrophil production by the bone marrow (when neutrophils are in high demand so B needs to increase production)
notesome drugs and toxins can cause similar morphological changes
- Some features of toxic change can develop with prolonged sample storage → ALWAYS assess
fresh blood smears (made shortly after collection) if looking for toxic changes!!!
What are the main toxic changes of neutrophils?
1) Increased cytoplasmic basophilia (dark grey/blue darker cytoplasm) - increased residual cytoplasmic RNA
2) Cytoplasmic vacuolation* - degranulation of lysosomes (can also occur as an artefact with storage)
3) Dohle bodies - grey-blue cytoplasmic inclusions, aggregates of rough endoplasmic reticulum (can also occur as an artefact with storage)
4) Toxic granulation - red granules in cytoplasm due to primary neutrophil granules taking up stain
5) Nuclear swelling
What is neutrophil hypersegmentation?
when neutrophils contain more than 5 lobes (normal neutrophils contain 5 nuclear lobulations)
What are the causes of nuclear hypersegmentation of neutrophils?
cause = hypercortisolaemia
- prolonged blood transit time with corticosteroid therapy, hyperadrenocorticism, or late stages of chronic inflammatory disease
- idiopathic finding in horses and goats
- others (e.g. cobalt deficiency in cattle, hereditary macrocytosis in poodles, etc.)
