VETN 110 - Leukocytes

Formation of leukocytes

leukopoiesis

hematopoietic stem cells

cell in the bone marrow that gives rise to all types of blood cells

Colony-stimulating factors (CSFs)

stimulate growth and differentiation of immature leukocytes in bone marrow

Where do WBCs develop?

bone marrow

Where do some WBCs develop?

Lymphoid tissues (lymphocytes)

Are WBCs constantly producing?

Yes

When are WBCs released?

As needed

Granulocytes

A group of leukocytes containing granules in their cytoplasm; neutrophils, eosinophils, basophils.

Agranulocytes

A group of leukocytes without granules in their nuclei; lymphocytes, monocytes.

Are there more or less WBCs than RBCs?

less

Physiological factors that affect WBC count

Stress, exercise, age

Pathological factors that affect WBC count

Infection (specifically bacterial), endocrine, immune-mediated (hypo or hyperactive immune system)

Function of WBCs

immunity

non-specific immunity

defenses that stop the invasion of pathogens; requires no previous encounter with a pathogen

What is the term for non-specific immunity?

Phagocytic

Cells involved in phagocytosis

Granulocytes (especially neutrophils) and monocytes

Phagocytosis

Cell eating

Specific Immunity

Targets specific antigens and creates a memory for future encounters

Cells involved in specific immunity

lymphocytes

B Cells

produce antibodies

humoral immunity

specific immunity produced by B cells that produce antibodies that circulate in body fluids

Where are antibodies found

plasma

T cells

Responsible for cell-mediated immunity

Cell-mediated immunity

type of immunity produced by T cells that attack infected or abnormal body cells

Cytokines

Signaling proteins that mediate immune responses.

natural killer cells (NK cells)

pursue diseased cells (such as those infected by viruses or cancer)

process of phagocytosis

1. Chemotaxis

2. Adherence

3. Ingestion

Chemotaxis

The attraction of phagocytic cells to an area of abnormality

Chemotaxins

chemical messengers that cause cells to migrate in a particular direction

Potent chemotaxins

Lipopolysaccarides & substances released by immune cells (macrophages and lymphocytes)

When does chemotaxis occur?

During inflammatory responses and infections

Adherence

The phagocytic cell sticking to the target it intends to engulf

How is adherence achieved?

Receptors on the surface of the phagocytic cell that bind to specific components on the surface of the target organism

Opsonization

coating antigen with antibody enhances phagocytosis

Engulfment (endocytosis)

The phagocytic cell engulfs the adhered target

What is released once the target organism is engulfed?

Powerful enzymes that kill or destroy the engulfed material

Neutrophil

A type of white blood cell that engulfs invading microbes and contributes to the nonspecific defenses of the body against disease.

What species are neutrophils most common in?

Dogs, horses and cats

Appearance of a neutrophil

1. Granulated (pale pink) abundant cytoplasm

2. Dark, lobulated nucleus

Heterophil

A leukocyte of avian, reptile, and some fish species that contains prominent eosinophilic granules; functionally equivalent to the mammalian neutrophil

maturation of neutrophils takes how long?

3-6 days

Proliferating pool (bone marrow)

contains cells of granulocytic series that are capable of division

Neutrophil maturation sequence

myeloblast, promyelocyte, myelocyte, metamyelocyte (juvenile), band (stab), segmented neutrophil

Maturation pool (bone marrow)

Cells continue tonmature

storage pool (bone marrow)

Consists of mature neutrophils awaiting release, holds about a 5 day supply

Intravascular pool (blood vessels)

Consists of the circulating pool and marginated pool

Circulating pool

Consists of freely moving neutrophils, this is the pool sampled from when blood is drawn

Marginated pool

Cells that are bumping and rolling against the walls of the blood vessels - preparing to enter tissues

Diapedesis

the passage of blood cells through the intact walls of the capillaries, typically accompanying inflammation.

What does a high neutrophil count signify?

A bacterial infection

Neutrophilia

increase in neutrophils

Leukocytosis

increase in the number of white blood cells

Do neutrophils divide?

No, once they mature they do not divide.

Granule depletion

The granules within a neutrophil deplete over time

Degenerative left shift

DEcrease in mature cells, INcrease in immature cells

What viral diseases can cause a severe drop in neutrophils

Feline leukemia and canine parvovirus

Effect of stress on neutrophil count

Stress triggers the release of steroids and epinephrine into the blood stream which cause neutrophils from the marginated pool to be released into the circulating pool

Eosinophil

white blood cell containing granules that stain red

Appearance of eosinophil in canine

Light, round (except in greyhounds)

appearance of eosinophils in a feline

Darker, small rods

Appearance of eosinophils in equines

Intense, large, round

Appearance of eosinophils in bovines, ovines and porcines

Red to pink, small and round

The nucleus of an eosinophil

bilobed, dark-staining, surrounded by reddish cytoplasmic granules

How long does it take an eosinophil to mature

2-6 days

Proliferating pool eosinophil

Dividing: myeloblasts, promyelocytes and myelocytes

Maturing pool eosinophil

Non dividing: myelocytes, metamyelocytes and band cells

Storage pool eosinophil

Mature cells

How do eosinophil enter tissues

Diapedesis

functions of eosinophils

Anti- inflammatory response, immunity and phagocytosis

Eosinophil histamine inhibition

Granules contain substances that can inhibit histamine, acting as a natural antihistamine

Eosinophil allergic responses

Often associated with allergic reactions and mast cell degranulation

Eosinophils role in parasitic infections

Play a significant role in the immune response against parasites.

Eosinophilia

increase in eosinophils

Primary indicators of eosinophilia

An allergic response, parasitic infection

Eosinopenia

decrease in eosinophils

Basophils

A circulating leukocyte that produces histamine and heparin

Appearance of basophils

Contain blue/purple granules, are water soluble and nucleus is lobulated

Key substances released by basophils

Histamine (increased vascular permeability) and heparin (acts as an anticoagulant)

Basophilia

increase in basophils

Basopenia

deficiency in the number of basophils in the blood

Monocytes

An agranular leukocyte that is able to migrate into tissues and transform into a macrophage.

Maturation timeframe of a monocyte

24-36hrs

Where are monocytes found

circulating blood, not stored

How long does a monocyte stay in the circulating pool?

24-36hrs

Macrophages

Found within the lymph nodes, they are phagocytes that destroy bacteria, cancer cells, and other foreign matter in the lymphatic stream.

How do monocytes enter tissues

Diapedesis

Diapedesis

the passage of blood cells through the intact walls of the capillaries, typically accompanying inflammation.

MPS aka RES

Mononuclear Phagocyte System or Reticuloendothelial System

When do monocytes become macrophages?

when they leave circulation and enter the tissues

Giant cells

phagocytes that can engulf particles much larger than the typical macrophage

How do macrophages become giant cells

They coalesce (merge) to form giant cells

What do the presence of giant cells indicate

Chronic inflammatory conditions, indicating a prolonged immune response to persistent stimuli

Monocytes lifespan

several months; have the longest life span

Appearance of monocyte

Largest of WBC. Pleomorphic (changes shape) nucleus, cytoplasm vacuolated (clear circles). No granules in cytoplasm

Primary function of monocytes

phagocytosis

Non-specific and specific link

After phagocytizing a foreign substance, the macrophage will present antigens from that substance on their cell surface, these are then presented to lymphocytes, signaling them to produce antibodies against the specific antigen.

chemotactic factors

attract phagocytes to area of inflammation

Monocytosis

increase in the number of monocytes,indicative of an inflammatory reaction in the body

Lymphocytes

A type of white blood cell that make antibodies to fight off infections

What species are lymphocytes predominant in?

Bovine and porcine