Leucocytes (white blood cells) are present in the blood stream for a rather short period of time; after that they migrate to other tissues to exert their functions and, finally, to die. They participate in reactions where the body needs a defense. Their cell count for 1 l of the whole blood is 3.8-9.0×10⁹. The cells are classified into granulocytes and agranulocytes.

Granulocytes

• lose the ability to proliferate when completing their bone marrow development
• have segmented, band-shaped, or horseshoe-shaped nuclei
• contain specific and non-specific (azurophilic) granules in the cytoplasm
• are further classified (by granule staining properties) into neutrophils, eosinophils and basophils

Agranulocytes

• maintain their proliferative potential when migrating from the bone marrow
• have no nuclear segmentation
• have no specific granules in the cytoplasm, though they can contain some azurophilic granules
• are further classified into lymphocytes and monocytes

Neutrophils

(azure II and eosin)

• In blood smears, their diameter is 10-12 μm
• Their nuclei have 3-5 segments connected by thin bridges (segmented type); some of the nuclei are С-shaped or S-shaped (stab cells) or bean-shaped (juvenile cells)
• The cytoplasm stains as slightly oxyphilic
• Granules are tiny and are difficult to distinguish
• Specific granules comprise cationic proteins, lysozyme, lactoferrin, collagenase, elastase, and alkaline phosphatase
• Azurophilic granules comprise acid hydrolases and myeloperoxidase

Segmented neutrophils q.v. #1, #2, #3. Stab cells q.v. #1, #2, #3

In females, the nuclei of neutrophils can contain Barr bodies or sex chromatin consisting of inactivated X chromosome.

The lifespan of neutrophils in the blood stream is 8-12 hours; then they exert their functions in loose connective tissue for 5-7 days. The key function is phagocytosis of bacteria. Their relative count is 65-70% of total WBC number, including segmented cells 60-65%, stab cells 3-5%, juvenile cells ≤ 0.5%.

For more details see Electron microscopy image of neutrophils

Eosinophils

(azure II and eosin)

• In blood smears, the diameter is 12-14 μm
• The nucleus includes 2-3 segments but band-shaped cells are also found
• The cytoplasm contains large eosinophilic granules
• Specific granules (eosinophilic ones) consist of major basic protein, histaminase, cationic proteins, and peroxidase
• Azurophilic granules consist of arylsulfatase, acid phosphatase, and other hydrolases

Segmented eosinophils q.v. #1, #2. Band-shaped eosinophil q.v.

Eosinophils remain in the peripheral blood for less than 12 hours, though rest for a fortnight in other tissues. Their action is anti-inflammatory; they destroy helminths and protozoa by extracellular ways. Their cell blood count is 1-5% of the total WBC number.

For more details see Electron microscopy image of an eosinophil

Basophils

(azure II and eosin)

• In blood smears, the diameter is 10-12 μm
• The nucleus contains mostly two segments, seldom S-shaped
• The cytoplasm contains large specific granules stained by azure II exhibiting metachromasia
• Specific granules contain heparin, histamine, anaphylatoxin, peroxidase, and eosinophil & neutrophil chemotactic factors
• Azurophilic granules consist of hydrolases

Basophils q.v. #1, #2

The lifespan of basophils in the blood is limited to 6-12 hours; however, their residence in tissues is for 1-2 days. The cells upregulate inflammatory reactions. Their cell blood count is ≤ 1% of the total WBC number.

For more details see Electron microscopy image of a basophil