Leukocytes

What are the main functions of neutrophils?

Inflammatory response

Innate immune response

What are the different pools of neutrophils in peripheral circulation?

Marinating Pool and Circulating Pool

Which pool is represented in a blood sample?

Circulating pool

What are the different pools of neutrophils in the bone marrow?

Proliferative

Maturation only

Storage

What are the differences between cells in each compartment of the bone marrow?

The proliferative pool has dividing cells, while those in the other pools don't divide

What type of cells are in the proliferative pool?

Myeloblast

Progranulocyte

Myelocyte

What type of cells are in the maturation and storage pools?

Metamyelocyte

Band neutrophil

Neutrophil

What are the kinetics of neutrophils in health?

- transit time in marrow is 7-10 days

- 4-6 times as many cells in the maturation pool than the proliferative pool

- storage pool has a relatively large supply

- blood transit time: 6-10 hours

- tissue lifespan: 24-48 hours

- destroyed by macrophages in tissue (90%)

- lost in secretions from mucuous membranes (10%)

What are cytokines important for?

They stimulate the production and differentiation of stem cells

What is a left shift?

An increase in immature neutrophils in the blood

What classifies a regenerative left shift?

segs > non-segs (mature > immature)

bone marrow is able to keep up

leukocytosis due to neutrophilia

What classifies a degenerative left shift?

non-segs > segs

bone marrow not keeping up

leukopenia due to neutropenia

What is the hallmark of acute inflammatory neutrophilia?

Left shift in circulation

What is a toxic change in neutrophils?

Accelerated neutrophil production that results in aberrant granulopoiesis

Occurs due to increased stimulus for neutrophil production

What are some characteristics of toxic changes in neutrophils?

- Döhle body

- Diffuse cytoplasmic basophilia

- Foamy cytoplasm

- Hyalinized nucleus

What causes acute inflammatory neutrophilia?

An increased need for neutrophils, which uses up the storage pool and increases stimulus for production

What two things help determine the balance of dynamics in determining blood neutrophil concentration?

Marrow delivery rate and tissue consumption rate

When is acute inflammatory neutrophilia expected?

It's expected with significant inflammation of internal or subcutaneous tissue (i.e. infection, necrosis, immune-mediated disease)

When would acute inflammatory neutrophilia not be seen or expected?

- Lower UTIs

- Superficial cutaneous lesions or oral cavity

- Inflammation of the brain and spinal cord

What is chronic inflammatory neutrophilia mediated by?

Cytokines from inflammatory site ongoing for at least 1 week

What are the characteristics of chronic inflammatory neutrophilia?

- Granulocytic hyperplasia (increased production)

- Increased release from storage pool

- Increased migration to tissues

What causes glucocorticoid-associated (or stress) neutrophilia?

The effects of steroids (cortisol, prednisone, prednisolone...)

What is the hallmark of glucocorticoid-associated neutrophilia?

A shift from the marginating to the circulating pool, without migration to the tissues (decreased ability of margination)

What are hypersegmented neutrophils and when are they seen?

They are neutrophils with 5 or more definitive lobes

Seen with the use of steroids and following stress (glucocorticoid-associated neutrophilia)

What causes Excitement/Physiologic Neutrophilia?

Catecholamines: epinephrine, norepinephrine

What are characteristics of excitement/physiologic neutrophilia?

- shift from marginating to circulating pool with no left shift

- transient, goes away when the animal calms down

What is the difference between the pools in peripheral circulation for cats and dogs?

Cats have a marginating pool with 3 times as many neutrophils than in the circulating pool

Why does severe, overwhelming, acute inflammatory neutropenia occur?

Migration of neutrophils to inflamed tissue exceeds the release of neutrophils from the marrow; The bone marrow is not able to keep up

What is seen with a severe, overwhelming, acute inflammatory neutropenia?

- increased migration to the tissues

- neutropenia with a left shift

- cytokines released from inflammatory site

- increased release of neutrophils from storage and maturation pools

What is an additional mechanism in severe gram-negative infections?

Endotoxins stimulate sequestration of neutrophils in the marginating pool --> neutropenia can be more severe as neutrophils shift from circulating to marginating pools so levels will be extremely low --> will see as acute overwhelming inflammatory neutropenia

When does granulocytic hypoplasia neutropenia occur?

When bone marrow cells or cells of the microenvironment are damaged --> lack of development

What can cause granulocytic hypoplasia?

Marrow disease causing decreased neutrophil production (i.e. infections, neoplastic, toxic, necrosis, myelofibrosis, drugs)

What is seen with granulocytic hypoplasia?

- persistent neutropenia

- usually NO left shift

- maturation is complete and orderly, but significantly decreased

- not an increased need, they just aren't being produced

What is common with granulocytic hypoplasias?

Bi- and pancytopenia

When does ineffective production neutropenia occur?

When neutrophil precursors are defective/damaged and die BEFORE release --> something wrong with development of cells

What can be seen with ineffective production neutropenia?

- lack of orderly and complete maturation of neutrophil sequence

- "maturation arrest"

What can cause ineffective production neutropenia?

immune-mediated, drugs, G-CSF deficiency

What can cause peripheral destruction neutropenia?

Immune mediated disease or hemophagocytic syndrome; This is RARE

What is seen with peripheral destruction neutropenia?

- Increase release from storage and maturation pools

- Neutrophils with antibodies that are quickly removed from circulation

Why is it more difficult for ruminants to respond to infection or inflammation?

They have a low marrow reserve and a slow regenerative capacity. Neutropenia is a common finding regardless of severity

How do cattle respond to acute inflammatory lesions?

- Neutrophils are consumed from blood and marrow within hours --> neutropenia that lasts for a few days

- After that time, repopulation of blood with neutrophils, with a left shift, occurs as marrow production increases

What are the recirculation times for lymphocytes?

Average blood transit time ~ 30 minutes

Total recirculation time ~ 1 to several hours

Do you see plasma cells in the blood in health?

No

How do lymphocytes circulate in the blood?

- Between lymph nodes and other lymphoid organs/tissue

- Distributed between marginating and circulating pools

What are the 3 major causes of lymphocytosis?

Chronic inflammation (lymphopoiesis d/t chronic antigenic stimulation)

Physiologic lymphocytosis (catecholamines)

Lymphoid neoplasia

What can chronic inflammation lymphocytosis be caused by?

bacterial/viral/fungal/protozoal infections

What can physiologic lymphocytosis be caused by?

fight or flight response, catecholamine injections (epinephrine or NE), and is most common in young animals, cats, and horses

What is seen with chronic inflammatory lymphocytosis?

- chronic antigenic or cytokine stimulation

- increase production (lymphopoiesis)

- neutrophilia (usually mature)

- monocytosis

- occasionally +- eosinophilia and/or basophilia

- maybe reactive lymphocytes

What are reactive lymphocytes?

- immune-stimulated lymphocytes

- upregulated synthesis --> inflammatory mediators and immunoglobulins

- active, systemic antigenic stimulation secondary to both infectious and noninfectious disorders

- larger lymphocytes than normal

What is seen with physiologic lymphocytosis?

- shift from marginating to circulating pool

- usually lasts minutes to hours

- no reactive lymphocytes

What is seen with lymphoid neoplasia?

- increase production of neoplastic lymphocytes in the marrow (leukemia)

- increase production of neoplastic lymphocytes in the tissue or lymph node (lymphoma)

- usually atypical, often medium or large lymphocytes

What are the 2 common causes of lymphopenia?

acute inflammation and corticosteroids

How can acute inflammation lymphopenia be caused?

- homing

- increased migration to inflamed tissue

How can corticosteroids cause lymphopenia?

low dose --> cells stay in tissues

high dose --> kill lymphocytes

stress leukogram

What is seen with acute inflammatory lymphopenia?

- increased migration to inflamed tissues

- increased migration from lymph node to blood

- "homing" to lymph nodes

- decreased movement of lymphocytes from lymph vessel to blood

- often neutrophilia with left shift

What can be seen with steroid lymphopenia?

- mature neutrophilia

- +/- monocytosis and/or eosinopenia

- decreased lymphopoiesis

- decreased efflux from lymph node into blood

- immediate shift from circulating pool to marrow and lymph node

- cytotoxic effects if high enough dose

What is the blood transit time of monocytes?

18-24 hours

What can cause monocytosis?

- acute and chronic inflammation

- steroid (stress) response --> mainly in dogs

How can you differentiate between a neutrophil and a monocyte?

Monocytes have clear/pale vacuoles

What are the characteristics of eosinophils?

- contain proteins that bind and damage parasite membranes

- important in allergic inflammation and immune-complex reactions

- not protective against bacterial infections

What is the blood transit time of eosinophils?

30 minutes - 12 hours --> long lived in tissues, but may not show up in blood

What can cause eosinophilia?

- hypersensitivity

- parasitic diseases

- mast cell degranulation

- Addison's disease

- hypereosinophilic syndrome

- paraneoplastic eosinophilia

What can cause eosinopenia?

- corticosteroids --> kill eosinophils

- Cushing's

What do basophils contain?

histamine and heparin

What role do basophils play?

- type-1 hypersensitivity

- delayed-type hypersensitivity

- proinflammatory

What do the nuclei of basophils look like?

lobulated or ribbon like, NOT round

What can cause basophilia?

- hypersensitivity

- parasitic disease

- neoplasia

What are the functions of mast cells?

promote hypersensitivity reactions, stimulate T cells, host defense against parasites, promote acute and chronic inflammatory responses

What do you need for a leukogram assessment?

- properly collected and handled blood

- anticoagulated blood (EDTA for mammals, heparin green top for avian and reptiles)

- Total WBC

- well-made blood smear

- differential cell counts

- cell morphology evaluation

How long does it take granulocytic hyperplasia (neutrophilia) to become evident in peripheral blood in ruminants?

At least 5 days --> small storage pool of neutrophils in bone marrow