Leukocytes Development, Kinetics and Functions

Granulocyte Maturation

1. Myeloblast

2. Premyelocyte

3. Myelocyte

4. Metamyelocyte

5. Band Form

6. Mature Granulocyte

Myeloblast - Nucleus

• Round to oval

• Centrally located

• Homogenous with delicate euchromatin with 2-4 visible nucleoli

Myeloblast - Cytoplasm

• slightly basophilic

• Type I: no visible granules

• Type II: up to 20 azurophilic granules

Myeloblast Cell Division and Bone Marrow Population

• Capable of cell division

• 1 - 2% Bone Marrow population

Type I Myeloblast

Type II Myeloblast

Promyelocyte - Nucleus

• Round to oval

• Eccentric Location

• Chromatin Clumping becomes visible, but nucleoli may still be seen

Promyelocyte - Cytoplasm

• Evenly basophilic

• Full of primary azurophilic granules

Promyelocyte Cell Division & Bone Marrow Population

• Capable of Cell division

• 1 - 6% bone Marrow Population

Promyelocyte

Myelocyte - Nucleus

• Nucleoli are difficult to observe using light microscope

Myelocyte - Cytoplasm

• End of primary (azurophilic) granule production

• Start of secondary (specific) granule production

• “Dawn of Neutrophilia”

Myelocyte Cell Division & Bone Marrow Population

• Final stage where cell division occurs

• 6 - 17% Bone Marrow Population

Myelocyte

Metamyelocyte - Nucleus

• Increasingly clumped chromatin

• Nuclear indentation (<1/2 of the nuclear diameter)

Metamyelocyte - Cytoplasm

• Start of tertiary granule synthesis

• Little to no basophilia

Metamyelocyte Cell Division & Bone Marrow Population

• No longer capable of Cell Division

• 20 - 30% Bone Marrow Population

Granules appear neutrophilic (attracts both acids and basophilic stain)

Metamyelocyte

Metamyelocyte

Band or Stab Form Nucleus

• Highly clumped chromatin

• Nuclear Indentation (>1/2 of the nuclear diameter)

Band or Stab Form - Cytoplasm

• Start of secretory granule formation

• All evidence of cytoplasmic basophilia are absent

Band or Stab Form Cell Division & Bone Marrow Population

• No longer capable of Cell Division

• 9 - 32% of the population

Band or Stab Form

Mature Neutrophil - Nucleus

• 3-4 nuclear segments connected by thread-like filaments

• Barr bodies

Mature Neutrophil - Cytoplasm

• Secretory granules continue to be formed

Mature Neutrophil Cell Division & Bone Marrow Population

• No longer capable of cell division

• 7 - 30% of Bone Marrow Population

Mature Neutrophil

Primary Neutrophil Granules

• Myeloperoxidase

• Acid Beta-glycerophosphates

• Cathepsins

• Defensins

• Elastase

• Proteinase - 3

In-charge of turning Chloride to hypochlorous acid (that engulf microorganism)

Myeloperoxidase

Secondary Neutrophil Granules

• Beta2 - microglobulin

• Collagenase

• Gelatinase

• Lactoferrin

• Neutrophil gelatinase-associated lipocalin

Sequests Iron

Lactoferrin

Tertiary Neutrophil Granules

• Gelatinase

• Collagenase

• Lysozyme

• Acetyltransferase

• ß2-microgIobulin

Secretory Neutrophil Granules

• CD 10, 13, 14, 16

• CD 11b/CD18

• Cytochrome b558

• ALP

  • Vesicle-associated membrane-2

  • Complement Iq receptor

  
  

• CRI

Neutrophil Functions

1. Phagocytosis

2. Formation of neutrophil extracellular traps

3. Secretion of transcobalamin 1 or R binder protein

Process of engulfing and destroying foreign particles by phagocytic cells

Phagocytosis

Phases of phagocytosis

1. Initiation or recognition

2. Chemotaxis

3. Engulfment

4. Digestion

• Phagocyte receptors recognize and bind to certain foreign molecular patterns and opsonin

• Surface receptors

Phagocytosis - Initiation

• Cellular movement towards or away from a chemical stimulus

• Chemotaxins/Chemotactic Factors/Chemoattractants

Phagocytosis - Chemotaxis

• Pseudopods are extended around the foreign particle and enclose it within a phagosome

Phagocytosis - Engulfment

Specialized vesicle formed inside a cell, acting as a temporary stomach to break down engulfed materials

Phagosome

Destroying foreign particles via O2 - dependent (ROS) and O2 - independent (primary and secondary granules)

Phagocytosis - Digestion

Neutrophil Extracellular Traps

• Generated upon neutrophil death as a result of antibacterial activity.

• Extracellular thread-like structure that represent chains of nucleosomes from unfolded nuclear chromatin materials

• Cytoplasmic enzymes attach to the Cathepsin G chromatin threads so that bacteria are digested in the external environment.

Eosinophils

• 1-5% of circulating leukocytes.

• Nucleus has only two segmentation.

• Cytoplasm is full of eosinophilic secondary granules.

Eosinophil Functions

• Destroys tissue-invading parasites through secretion of MBP, ECP, and ROS

• Play an important role in immune regulation.

• Regulate mast cell function through the release of MBP that causes the mast cells to degranulate.

• Hallmark of allergic disorders.

Basophils

• Least numerous white blood cell (0.2% - 1.5%)

• Lobulated nucleus obscured by large basophilic granules

• Involved in allergic responses.

• Regulates Th2 responses and induce lgE production.

Basophil Granules

1. Histamine

2. Platelet Activating Factor

3. Leukotriene C4

4. Ineterleukin-4 and -13

5. Vascular Endothelial Growth Factor (A and B)

6. Chondroitin Sulfates

Pro-inflammatory Substances

1. Histamine

2. Leukotriene C4

Mast Cells

• Found in tissues.

• Precursors also arise from GMP

• Involved in allergic responses

• Also has anti-inflammatory and immunosuppressive actions

Inactive Macrophages with no peroxidase

Monocyte

Monocyte Maturation

1. Monoblast

2. Promonocyte

3. Monocyte

Promonocyte - Nucleus

• Slightly Folded or Indented

• Delicate chromatin pattern

Promonocyte Cytoplasm

Blue with scattered azure granules

Monocyte - Nucleus

• Deeply Indented (“Horseshoe” or “Kidney bean” shaped)

• Lace-like or stringy chromatin Pattern

Monocyte - Cytoplasm

Blue-gray with fine azure granules (“ground glass” appearance)

Monoblast

Promonocyte

Monocyte

Macrophage

• Oval nucleus with net-like chromatin pattern

• Vacuolated cytoplasm

Macrophage Function

1. Phagocytosis

2. Antigen presentation

Macrophages of the Brain

Microglia

Macrophages in the Tissues

Histiocytes

Liver Macrophages

Kupffer cells

Lung Macrophages

Alveolar Macrophage

Bone Macrophage

Osteoclasts

Spleen Macrophage

Splenic Macrophages

Macrophage of the skin

Langerhans cells

Macrophages of placenta

Hofbauer Cells

Lymphocyte Maturation

1. Lymphoblast

2. Prolymphocyte

3. Lymphocyte

Lymphoblast - Nucleus

• Round to oval

• Coarse Chromatin

• 1-2 nucleoli

Lymphoblast Cytoplasm

Moderate to deep blue

Prolymphocyte Nucleus

• Round to oval

• Slightly indented

• Clumped chromatin

• 1-2 nucleoli

Prolymphocyte Cytoplasm

Moderate to deep blue to occasional azurophilic granules

Lymphoblast

Prolymphocyte

Lymphocyte

B - cell

• 10 - 15% of circulating lymphocytes

• Homogenous chromatin material

• Extremely scanty cytoplasm

• Adaptive humoral immunity

• Produces antibodies

T - cell

• 85% of circulating lymphocytes

• Morphologically indistinguishable from B cells in the PBS

Helper T-cell

• Commands cytokines

• CD4+ cell

Cytotoxic T - cell

• kills virus infected cell/tumor cell

• CD8+ T - cell

• antigen - specific/ antigen dependent

Regulatory T - cells

T - suppressor cells

Natural Killer Cell

• 2% of circulating lymphocytes

• Large and granular

• Innate defense against intracellular pathogens

• antigen - independent

• non - specific

Subsets of CD16+ and CD56+

NK Cell

CD4+ surface marker

Helper T - cell

CD8+ surface marker

Cytotoxic T - cell

Emit Robin Egg Blue

Lymphocyte