Leukocytes and Their Functions

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Questions and Answers

What is the typical circulating half-life of eosinophils in the blood?

2 to 5 hours

72 hours

18 hours (correct)

12 hours

Which of the following functions is NOT associated with eosinophils?

Regulates mast cell formation through release of major basic protein

Acts as antigen presenting cells (APCs)

Can induce Type 1 or 2 immune response

Phagocyte large pathogens in a manner similar to macrophages (correct)

During which stage are secondary (specific) granules in neutrophils formed?

Promyelocyte stage

Myelocyte stage (correct)

Segmentation stage

Metamyelocyte stage

Which of the following conditions can lead to an increase in eosinophil production?

Helminthic infection Signup and view all the answers

What is the primary role of tertiary granules in neutrophils?

First to be released upon activation Signup and view all the answers

What implication do eosinophils have in allergic disorders?

They induce airway remodeling Signup and view all the answers

Which statement best describes the kinetics of basophils?

Their kinetics are poorly understood due to their small numbers Signup and view all the answers

What type of immune response do eosinophils primarily induce?

Type 2 immune response Signup and view all the answers

What are the two pools that neutrophils can be divided into once in the blood?

Circulating Neutrophil Pool and Marginated Neutrophil Pool Signup and view all the answers

Which factor does NOT influence the leukocyte population?

Genetic predisposition Signup and view all the answers

What is the primary function of eosinophils?

Destruction of parasitic infections Signup and view all the answers

How long is the half-life of neutrophils in the blood?

7 hours Signup and view all the answers

What mechanism allows neutrophils to enter tissues from the Marginated Neutrophil Pool?

Diapedesis Signup and view all the answers

Which process is primarily responsible for the destruction of foreign materials by neutrophils?

Phagocytosis Signup and view all the answers

Neutrophils can enhance immune responses by activating which system?

Complement system Signup and view all the answers

The lifespan of neutrophils in tissues varies depending on what factor?

Response to infection or inflammation Signup and view all the answers

What is a key function of monocytes in innate immunity?

Synthesize nitric oxide to combat various pathogens Signup and view all the answers

Which of the following correctly describes the life span of macrophages?

Depends on their response to inflammation or infection Signup and view all the answers

How do mast cells contribute to the immune response?

They mediate allergic responses and inflammatory reactions Signup and view all the answers

What occurs to promonocytes during increased demand for monocytes?

They can produce up to 16 monocytes in 60 hours Signup and view all the answers

What distinguishes dendritic cells in relation to antigen presentation?

They interact with and activate T and B lymphocytes Signup and view all the answers

What is NOT a function of macrophages?

Producing insulin to regulate blood sugar Signup and view all the answers

Where do monocytes primarily mature into macrophages?

In peripheral blood or tissues Signup and view all the answers

What happens to monocytes once they enter the tissues from the circulation?

They can grow to a diameter of 40-50um Signup and view all the answers

Study Notes

Leukocytes l

Leukocytes are also known as white blood cells
They are derived from being colorless compared to red blood cells
They are the main component of the buffy coat, which appears white in color
There are at least 10 different types of leukocytes

Function

Their major function is a defense mechanism
They are part of the innate (non-specific) immune system
They can activate the complement system
Their major function is phagocytosis and destruction of foreign materials and microorganisms
This process involves seeking (chemotaxis, motility, and diapedesis) and destruction (phagocytosis, digestion)

Leukocyte Staining

Granulocytes are a group of leukocytes with cytoplasmic granules and lobulated or segmented nuclei
Eosinophils are acidic granules that stain with acid stains (eosin)
Basophils have acidic granules that stain with basic stains (methylene blue)
Neutrophils have granules that react with both acidic and basic stains, resulting in a pink to lavender color

Mononuclear cells/Agranulocytes

Mononuclear cells/agranulocytes have round, oval, indented, or folded nuclei

Leukocyte Population

Factors influencing leukocyte population include sex, age, activity, time of day, and ethnicity
White blood cells (WBCs) react to stress, being consumed, or being destroyed
There needs to be enough production

Granulocytes

Granulocytes are a group of leukocytes characterized by their granules, which are cytoplasmic
They have lobulated or segmented nuclei

Neutrophils

Neutrophils contain nonspecific granules
Red blood cells (RBCs) are shown in the image for comparison

Kinetics

Once in the blood, neutrophils are divided into circulating neutrophil pool (CNP) and marginated neutrophil pool (MNP)
MNP neutrophils are loosely localized to the walls of capillaries in tissues such as the liver, spleen, and lungs
MNP and CNP neutrophils are roughly equal in number and exhibit no difference in function
Neutrophils in the blood have a half-life of 7 hours
MNP can enter tissues through diapedesis, while those that don't migrate will undergo apoptosis and be removed by splenic macrophages, which is dependent on whether they respond to infection or inflammation
In response to infection or inflammation, the neutrophils have a longer lifespan, otherwise, they have varying half-lives measured in hours

Eosinophils

Eosinophils have a circulating half-life in the blood of roughly 18 hours
Their tissue destination is the underlying, epithelial surfaces in the respiratory, gastrointestinal, and genitourinary tracts
In tissues their life span can range from 2 to 5 days
They have multiple functions, including compound exocytosis, piecemeal degranulation, acting as antigen-presenting cells (APCs), and inducing Type 1 or 2 immune responses
Eosinophils regulate mast cell formation through the release of major basic protein (MBP)
They destroy tissue-invading helminthes and prevent reinfection
They're associated with asthma, and inflammation of the airways

Basophils

Basophil kinetics is difficult to understand due to their low numbers
A mature basophil has an estimated lifespan of 60 hours, governed by anti-apoptotic pathways
They've been historically categorized as less important than mast cells in allergic reactions, but they share some similarities, including IgE receptors, and they do contain histamine in their secondary granules
Basophils participate in controlling helminth infections in conjunction with eosinophils

Mast Cells

Mast cells are not leukocytes but tissue effector cells in allergic and inflammatory responses
They share phenotypic and functional similarities with basophils and eosinophils
They develop in peripheral blood and tissues
Mast cells have anti-inflammatory and immunosuppressive functions

Agranulocytes/Mononuclear Cells

These cells include white blood cells (WBCs) with no visible granules and single or multiple nuclei
Examples include lymphocytes, monocytes and macrophages

Monocytes/Macrophages

Promonocytes may experience two mitotic divisions within 60 hours to produce approximately 4 monocytes
When there's a high demand, 16 monocytes can form within 60 hours.
Monocytes circulate for roughly 3 days before entering tissues and differentiating into macrophages.
Their size reaches between 40 and 50 micrometers in diameter
The lifespan of macrophages varies based on whether they're responding to inflammation or infection, or are acting as "resident" macrophages, such as Kupffer cells or alveolar macrophages, which may live longer in their tissues
Monocytes/Macrophages functions include innate immunity, adaptive immunity, and housekeeping functions

Innate Immunity

Monocytes/Macrophages recognize many bacterial pathogens, stimulating an inflammatory response, releasing cytokines, and phagocytosing items
They produce nitric oxide, which is cytotoxic to viruses, bacteria, fungi, protozoa, helminths, and tumor cells
They possess Fc receptors to phagocytosing foreign materials coated with antibodies (Abc) or complement

Adaptive Immunity

Both macrophages and dendritic cells are responsible for presenting antigens and fragments (APCs) for activating T and B lymphocytes that initiate adaptive immune responses, where dendritic cells are most efficient
They are capable of degrading antigens for immune response activation

Housekeeping Functions

Monocytes/Macrophages remove dead cells, debris, and dead cells from areas of infection and tissue damage
They destroy senescent red blood cells (RBCs)
They synthesize and maintain a variety of proteins, including coagulation factors, complement components, cytokines, growth factors, and enzymes

Lymphocytes

Lymphocytes are divided into three major groups: T cells, B cells, and NK cells
T and B cells are key players in adaptive immunity, while NK cells are part of innate immunity
Lymphocytes are not end cells, but resting cells that can multiply into memory and effector cells to respond to stimulation
They recirculate between the bloodstream and tissues
B and T cells can modify antigen receptor segments to create a variety of antibodies and surface receptors
T and NK cells develop and mature outside the bone marrow (BM)
Lymphocyte functions and kinetics are part of immunology

WBC Anomalies and Leukemia

Morphological abnormalities in WBCs can indicate conditions like leukemia.

Morphological Abnormalities

Normal morphology examples of various white blood cell types (WBCs): Lymphocyte, Monocyte, Basophil, Eosinophil, Neutrophil are shown with diagrams and micrographs
Pelger-Huet Anomaly: neutrophils with hypolobulated, rounded nuclei, condensed chromatin; thin chromatin strands may connect the lobes to make a pinch-nez (spectacle) or, a wider bridge gives the appearance of a peanut
Hyper-segmented Neutrophil: neutrophils with more or higher number of nuclear lobes that are abnormal
Drumsticks: inactive X chromosome in females

Alder-Reilly Anomaly

Recessive disease.
Cytoplasmic deposition of mucopolysaccharides (lipids)
Appears as metachromatic granules

Chediak-Higashi Syndrome

Rare autosomal recessive trait
Abnormally large, peroxidase-positive lysosomes are seen in neutrophils and other cells
Result in albinism

May-Hegglin Anomaly

Rare autosomal dominant condition
Presence of large Dohle-body-like formations (combination of rods and granules that are ribosomally derived).

Dohle Bodies

Small blue-gray inclusions in neutrophil cytoplasm, often at the margins
Composed of rough endoplasmic reticulum and glycogen granules
Associated with inflammatory disorders and burns

Toxic Granulation

Larger, more basophilic granules than normal are present in neutrophils
Common in severe bacterial infections, burns, malignancies, and drug reactions.

Reed-Sternberg Cells

Large cells with multi-lobed, characteristic "mirror-like" nuclei
Seen in Hodgkin's lymphoma

Hand-mirror cells

T cell characteristic with a 'hand-mirror' shape within T-cell acute lymphocytic leukemia

Sezary Cells

Lymphocytes with convoluted/folded nuclei
Seen in advanced mycosis fungoides

Smudge Cells

Fragile lymphocytes rupturing during preparation
Nuclei spread out, with hazy borders

Atypical Lymphocytes

Large lymphocytes with foamy or vacuolated cytoplasm
Irregular nuclei; commonly seen in viral infections like Herpes and HIV
Basophilic cytoplasm and coarse chromatin

Activated Monocytes

Associated with inflammatory reactions, like bacteremia
Increased granulation

Auer Rods

Red, needle-like structures of primary granules
Characteristic of acute myeloid leukemia (AML)

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Description

This quiz covers the essential aspects of leukocytes, also known as white blood cells, including their functions in the immune system and the different types identified through staining techniques. Test your knowledge on their roles in phagocytosis and immune defense.