(Draft) Important Remarks on Different Leukocyte Types

Neutrophil

Nucleus: 3 to 5 lobes (separated by filaments)

Neutrophil

Cytoplasm: Pink to tan with violet or lilac granules

Neutrophil

Most Common WBC in Peripheral Blood

Neutrophils (followed by monocytes)

First Phagocytes to Reach Infected Areas

Neutrophil

Move in a zigzag manner; change to a straight line path when near a chemotactic attractant/factor

GMP (Granulocyte-monocyte progenitor)

Common Progenitor of Neutrophils and Monocytes

G-CSF (granulocyte-colony stimulating factor)

Major Stimulatory Cytokine for Neutrophil Production

Approximately 7 hours

Half-life of Neutrophils in Blood

1. Phagocytosis and destruction of foreign material/microorganisms

2. Generation of NETs

3. Secretory function

Three Major Functions of Neutrophils

NETs

• extracellular threadlike structures thought to represent chains of nucleosomes from unfolded nuclear chromatin material (DNA)

• have enzymes from neutrophil granules attached to them

• able to trap and kill gram-positive and gram-negative bacteria as well as fungi

• are produced at the time that neutrophils die as a result of antibacterial activity

NETosis

Unique form of neutrophil cell death resulting in the release of NETs

Neutrophil

Source of cytokines and transcobalamin I / R binder protein (necessary for proper absorption of Vitamin B12)

Primary -> Secondary -> Tertiary -> Secretory

Order of Neutrophil Granule Formation

Secretory -> Tertiary -> Secondary -> Primary

Order of Neutrophil Degranulation

Primary -> Secondary -> Tertiary -> Secretory

Neutrophil Granule Size (Largest to Smallest)

Primary (Azurophilic) Granules

Granules Formed during promyelocyte stage; LAST to be released (exocytosis)

• Myeloperoxidase (MPO)

• Lysozyme (muramidase)

Primary Granule Contents ⭐️

Myeloperoxidase (MPO)

Exhibits bactericidal, fungicidal, and virucidal properties; detected by flow cytometry and cytochemical staining in myeloid precursors in acute leukemia

Lysozyme Synonym & Function

Muramidase; antimicrobial enzyme

Secondary (Specific) Granules

Formed during myelocyte and metamyelocyte stages

Secondary (Specific) Granules

Third to be released

• Gelatinase

• Lactoferrin,

• Transcobalamin I

• Lysozyme

Secondary (Specific) Granules Contents ⭐️

Lactoferrin

Iron-binding protein that competes with bacteria for iron

Tertiary (Gelatinase) Granules Stages & Release Order

Formed during metamyelocyte and band stages

Tertiary (Gelatinase) Granules

Second to be released

• Gelatinase

• Lysozyme

Tertiary (Gelatinase) Granules Contents ⭐️

Secretory Granules (Secretory Vesicles)

Formed during band and segmented neutrophil stages

Secretory Granules (Secretory Vesicles)

First to be released (fuse to plasma membrane)

• CD11b/CD18

• Alkaline phosphatase

Secretory Granules Contents

CD11b/CD18

Contributes to tight stationary binding between neutrophils and endothelial cells

Alkaline Phosphatase

used to differentiate Leukemoid Reaction (LR) vs CML

Neutrophil

is the ONLY WBC that has alkaline phosphatase activity

1. Stem cell pool (Hematopoietic stem cells)

2. Mitotic/Proliferation pool

3. Storage/Maturation pool

Bone Marrow Neutrophil Pools

• CMP (CFU-GEMM)

• GMP

• Myeloblast

• Promyelocyte

• Myelocyte (last stage capable of mitosis)

Neutrophil Mitotic (Proliferation) Pool Components

• Metamyelocyte

• Band

• Segmented neutrophils

Neutrophil Storage (Maturation) Pool Components

1. Circulating Neutrophil Pool (CNP) - found in the plasma

2. Marginal Neutrophil Pool (MNP) - found adhering to the blood vessel wall

Peripheral Blood Neutrophil Pools

CNP to MNP Ratio

50:50

Eosinophil

Nucleus: Dark purple, usually has two lobes

Eosinophil

Cytoplasm: Filled with large, spherical granules of uniform size that stain bright orange

IL-5

Most specific cytokine for eosinophil lineage

• promotes terminal maturation

• functional activation

• prevention of apoptosis

Underlying columnar epithelial surfaces in the respiratory, gastrointestinal, and genitourinary tracts

Eosinophil Tissue Destinations

Eosinophilia

Hallmark of allergic disorders

Major Basic Protein (MBP), eosinophil cationic protein, and reactive oxygen species

Eosinophil Destroys tissue-invading helminths by secretion of

Major Basic Protein (MBP)

Eosinophil Regulates mast cell function through release of ___ (causes degranulation and cytokine production) and produces nerve growth factor (promotes mast cell survival and activation)

Roughly 18 hours

Eosinophil Circulating Half-life

2 to 5 days

Eosinophil Tissue Survival Time ⭐️

• Formed during promyelocyte stage

• contain Charcot-Leyden crystal protein

Eosinophil Primary Granules Stage & Content

Eosinophil Secondary Granules Stage & Contents

Formed throughout remaining maturation; contain Major basic protein (core), Eosinophil cationic protein (matrix), Eosinophil-derived neurotoxin (matrix), Eosinophil peroxidase (matrix), Lysozyme (matrix), Catalase (core and matrix), Beta-Glucuronidase (core and matrix), Cathepsin D (core and matrix), Interleukins 2, 4, and 5 (core), Interleukin-6 (matrix), GM-CSF (core)

Eosinophil Small Lysosomal Granules Contents

Acid phosphatase, Arylsulfatase B, Catalase, Cytochrome b558, Elastase, Eosinophil cationic protein

Charcot-Leyden Crystals Definition & Morphology

Disintegration products of eosinophils; hexagonal, bipyramidal crystals

Charcot-Leyden Crystals Staining Characteristics

Colorless, but stain black in Hematoxylin, red in Eosin, and purplish red in Trichrome stain

Eosinophil Lipid Bodies Contents

Cyclooxygenase, 5-Lipoxygenase, 15-Lipoxygenase, Leukotriene C4 synthase, Eosinophil peroxidase, Esterase

Eosinophil Secretory Vesicles Function

Carry proteins from secondary granules to be released into the extracellular medium

Eosinophil Degranulation Methods

1) Classical exocytosis, 2) Compound exocytosis, 3) Piecemeal degranulation, 4) Cytolysis

Basophil Nucleus Features

Difficult to observe because of overlying granules; generally unsegmented or bilobed

Basophil Cytoplasm Features

Densely stained, dark violet to purple-black granules (variable in size and unevenly distributed)

Basophil Granules Major Contents

Histamine, Interleukin-4, Interleukin-13, Chondroitin sulfates (e.g., heparin)

Toluidine Blue Stain Principle

Binds with acid mucopolysaccharides in blood cells to form metachromatic complexes (reddish-violet color)

Toluidine Blue Diagnostic Value

Identifies basophils and mast cells, especially in neoplastic forms where granule count is reduced

Basophil Functions

IgE receptors on surface trigger granule release when cross-linked; induces B cells to synthesize IgE; controls helminth infections

Least Common WBC in Peripheral Blood

Basophil

Basophil Lifespan

60 hours

Mast Cell Distinction & Features

NOT leukocytes; connective tissue cells with large basophilic granules containing heparin, serotonin, bradykinin, and histamine

Monocyte Nucleus Features

Round, horse-shoe shaped or lobulated with folding/convolutions; "lace-like" or "stringy" chromatin; nuclear vacuoles may be present

Monocyte Cytoplasm Features

Abundant blue-gray with fine indistinct granules (azure dust / ground-glass appearance); pseudopods/blebs and vacuoles present

Largest Cell in Normal Peripheral Blood

Monocyte (2 to 3 times the diameter of an RBC)

Monocyte Identification (Histochemical)

Strong positive reaction with Non-Specific Esterase (NSE) stain (alpha-naphthyl acetate/butyrate esterase)

Monocyte NSE Fluoride Inhibition

NSE in monocytes is INHIBITED by sodium fluoride (unlike granulocytic/lymphocytic NSE)

Monocyte Enzyme Content

Rich in muramidase (lysozyme)

Promonocyte Mitotic Divisions & Output

Undergoes 2 divisions in 60 hrs (yields 4 monocytes); increased demand causes 4 divisions in 60 hrs (yields 16 monocytes)

Monocyte Peripheral Pools Ratio

Marginal pool of monocytes is 3.5 times the circulating pool

Lymphocyte Morphology

Nucleus: Deep purple, round, oval, or indented (nucleoli visible) | Cytoplasm: Sky-blue or "Robin egg" blue

Lymphocyte Origins & Subtypes

Bone marrow, thymus, and lymphatic system | T cells & B cells (adaptive immunity), NK cells (innate immunity)

Three Physiologic Characteristics of Lymphocytes

1) Predestined to migrate, 2) Heterogeneous group of cells, 3) NOT an obligate end cell (can be stimulated to divide)

Obligate End Cell Definition & Example

A mature cell committed to perform a function and then die (e.g., Neutrophil)

Variant Lymphocyte Features

Currently reacting against a specific antigen; dense to immature-looking nucleus, deeply basophilic to pale blue abundant cytoplasm; nonmalignant reactive disorders

Variant Lymphocyte Synonyms

Reactive lymphocytes, atypical lymphocytes, virocytes, stress lymphocytes, Downey cells, transformed lymphocytes, glandular fever cells

Type I Variant Lymphocyte

Aka Turk's Irritation Cell or Plasmacytoid Lymphocyte; seen in German Measles

Type II Variant Lymphocyte

Aka Infectious Mononucleosis Cell; characterized by "flared skirt" or "fried egg" appearance; seen in Infectious Mononucleosis

Type III Variant Lymphocyte

Characterized by finely reticulated nuclear chromatin pattern