Myeloblast

Granulocytes develop from the multipotential myeloid stem cell (CFU-GEMM) which differentiates into lineage-specific progenitor cells.

• CFU-G - gives rise to neutrophils
• CFU-Eo - gives rise to eosinophils
• CFU-Ba - gives rise to basophils

Myeloblasts are produced directly from these progenitor cells (CFU) under the influence of cytokines. They are the first recognizable precursor of granulocytes.

• Large cells (12 to 18 µm diameter)
• Large, round or oval nucleus (85 to 90% of cell) of euchromatin (fine, granular pattern)
• Small amount of cytoplasm that is pink-blue to light blue
• No granules

Myeloblasts of specific lineages cannot be distinguished from each other. They are rare cells that are difficult distinguish from other types of cells (for example, large lymphocytes).

• Myeloblast #1 (60x) [+]

• Myeloblast #2 (60x) [+]

• Myeloblast #3 (60x) [+]

Promyelocyte

The myeloblast matures into a promyelocyte.

Promyelocytes of different granulocyte lineages cannot be distinguished from each other.

• Larger cells (16 to 22 µm diameter)
• Round, oval or indented nucleus (65 to 80% of cell) with more condensed chromatin (a coarser, granular pattern)
• Increased amount of blue cytoplasm
• Azurophilic granules are only produced in this stage
• Capable of mitosis

Examples:

• Promyelocyte #1 (60x) [+] - just beginning production of azurophilic granules

• Promyelocyte #2 (60x) [+] - just beginning production of azurophilic granules

• Promyelocyte #3 (60x) [+] - many azurophilic granules

• Promyelocyte #4 (60x) [+] - many azurophilic granules

Neutrophilic Myelocyte

The neutrophilic promyelocyte matures into a neutrophilic myelocyte.

This is the first stage in which precursors of the different granulocyte lineages can be distinguished from each other because of the presence of specific granules.

• Larger cells (18 to 20 µm diameter)
• Round, oval or indented nucleus (50% of cell) with a coarser, granular pattern of chromatin
• Cytoplasm is lighter blue
• Specific granules appear for the first time
• Fewer azurophilic granules
• Last cell capable of mitosis

Examples:

• Neutrophilic Myelocyte #1 (60x) [+]

• Neutrophilic Myelocyte #2 (60x) [+]

• Neutrophilic Myelocytes #3 (60x) [+]

• Neutrophilic Myelocyte #4 (60x) [+]

Neutrophilic Metamyelocyte

The neutrophilic myelocyte matures into a neutrophilic metamyelocyte.

• Smaller cells (12 to 17 µm diameter)
• Nucleus is dented, kidney shaped (50% of cell) of mostly heterochromatin
• Cytoplasm ranges from blue-gray to pink-gray
• Pink-salmon specific granules
• Few azurophilic granules
• No longer capable of mitosis

Examples:

• Neutrophilic Metamyelocyte #1 (60x) [+]

• Neutrophilic Metamyelocyte #2 (60x) [+]

• Neutrophilic Metamyelocyte #3 (60x) [+]

• Neutrophilic Metamyelocyte #4 (60x) [+]

Band Neutrophil

The neutrophilic metamyelocyte matures into a band neutrophil.

• Smaller cells (10 to 12 µm diameter)
• Nucleus is elongated and often has a horseshoe-like ("U") appearance that contains heterochromatin
• Cytoplasm is a pale blue-pink
• Pink-salmon specific granules
• Few azurophilic granules
• No longer capable of mitosis

Examples:

• Band Neutrophil #1 (60x) [+]

• Band Neutrophil #2 (60x) [+]

• Band Neutrophils #3 (60x) [+]

• Band Neutrophil #4 (60x) [+]

Neutrophil

The band neutrophil develops into a mature neutrophil. Neutrophils phagocytose and destroy bacteria.

• 10 to 15 µm diameter)
• Segmented nucleus with three to five lobes
• Cytoplasm is a pale blue-pink
• Specific granules are pink-salmon
• Few azurophilic granules
• No longer capable of mitosis

Examples:

• Neutrophil #1 (60x) [+]

• Neutrophil #2 (60x) [+]

• Neutrophils #3 (60x) [+]

• Neutrophils #4 (60x) [+]

Mature neutrophils are released from bone marrow into the peripheral circulation. They circulate in blood for 8 to 16 hrs. Their tissue life span is only 1 to 2 days.