White blood cells (WBCs)

White blood cells (WBCs) or leukocytes are the colorless

and nucleated formed elements of blood (leuko is derived

from Greek word leukos = white). Alternate spelling for

leukocytes is leucocytes.

Compared to RBCs, the WBCs are larger in size

and lesser in number. Yet functionally, these cells are

important like RBCs because of their role in defense

mechanism of body and protect the body from invading

organisms by acting like soldiers.


WBCs differ from RBCs in many aspects. The differences

between WBCs and RBCs are given in Table 16.1.

1. Larger in size.

2. Irregular in shape.

3. Nucleated.

4. Many types.

5. Granules are present in some type of WBCs.

6. Lifespan is shorter.


Some of the WBCs have granules in the cytoplasm.

Based on the presence or absence of granules in the

cytoplasm, the leukocytes are classified into two groups:

1. Granulocytes which have granules.

2. Agranulocytes which do not have granules.

1. Granulocytes

Depending upon the staining property of granules, the

granulocytes are classified into three types:

i. Neutrophils with granules taking both acidic and

basic stains.

ii. Eosinophils with granules taking acidic stain.

iii. Basophils with granules taking basic stain.

2. Agranulocytes

Agranulocytes have plain cytoplasm without granules.

Agranulocytes are of two types:

i. Monocytes.

ii. Lymphocytes.



Neutrophils which are also known as polymorphs have

fine or small granules in the cytoplasm. The granules take

acidic and basic stains. When stained with Leishman’s

stain (which contains acidic eosin and basic methylene

blue) the granules appear violet in color.

Nucleus is multilobed (Fig. 16.1). The number of

lobes in the nucleus depends upon the age of cell. In

younger cells, the nucleus is not lobed. And in older

neutrophils, the nucleus has 2 to 5 lobes. The diameterof cell is 10 to 12 μ (Table 16.2). The neutrophils are

ameboid in nature.


Eosinophils have coarse (larger) granules in the

cytoplasm, which stain pink or red with eosin. Nucleus

is bilobed and spectacle-shaped. Diameter of the cell

varies between 10 and 14 μ.


Basophils also have coarse granules in the cytoplasm.

The granules stain purple blue with methylene blue. Nucleus is bilobed. Diameter of the cell is 8 to 10 μ.


Monocytes are the largest leukocytes with diameter of 14 to 18 μ. The cytoplasm is clear without granules. Nucleus is round, oval and horseshoe shaped, bean shaped or kidney shaped. Nucleus is placed either in the center of the cell or pushed to one side and a large amount of cytoplasm is seen.


Like monocytes, the lymphocytes also do not have granules in the cytoplasm. Nucleus is oval, bean-shaped or kidney-shaped. Nucleus occupies the whole of the cytoplasm. A rim of cytoplasm may or may not be seen.

Types of Lymphocytes

Depending upon the size, lymphocytes are divided into two groups:

1. Large lymphocytes: Younger cells with a diameter of 10 to 12 μ.

2. Small lymphocytes: Older cells with a diameter of 7 to 10 μ.

Depending upon the function, lymphocytes are divided into two types:

1. T lymphocytes: Cells concerned with cellular immunity.

2. B lymphocytes: Cells concerned with humoral immunity.

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