White Blood Cell
White blood cells or leukocytes (leucocytes), are cells of the immune system involved in defending the body against both infectious, diseases and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a haematopoietic stem cell (Brooks, 2008). They live for about three to four days in the average human body. Leukocytes are found throughout the body, including the blood and lymphatic system (Maton et al., 2002).
Types of White Blood Cell In The Study of White Blood Cell
There are several different types of WBCs, they all have many things in common, but are all distinct in form and functions. A major distinguishing feature of some leukocytes is the presence of the granules, white blood cells are often characterized by granulocytes and agranulocytes.
- Granulocytes (polymorphonuclear leucocytes): leukocytes characterized by the presence of different staining granules in their cytoplasm when viewed under light microscopy. These granules are membrane bound enzymes that act primarily in the digestion of endocytosed particles. There are three types of granulocytes: which are named according to their staining properties.
- Neutrophils:- Its main function is defence against bacteria
- Easipophils:- Kills parasites and have a role in allergic
- Basophil:- Not well understood but they function in allergic reaction
- Agranulocytes (Mononuclear leukocytes): Leukocytes characterized by the absence granules in their cytoplasm. Although the name implies a lack of granules these cells do contain non-specific azurophilic granules which are lysosomes (Gartner et al., 2007). The cell include;
- Lymphocytes:- They are the killer cells (B cells and T cells)
- Monocytes:- They enter the tissue, where they become larger and turn into macrophages.
But the neutrophil is the subject of interest in this experimental study.
Neutrophil granulocytes are the most abundant type of white blood cells in mammals and form an essential part of the innate immune system. Generally, they are referred to as either neutrophils or polymorphonuclear neutrophils (or PMNs), and are subdivided into segmented neutrophils (or segs) and banded neutrophils (or bands). They form part of the polymorphonuclear cell family together with basophil and eosinophils (Witko et al., 2002, Klebanoff et al., 1978, and Nathan, 2006). Normally neutrophils contain a nucleus divided into 2-5 lobes and are normally found in the blood stream. During acute phase of inflammation, particularly as a result of bacterial infection, environmental exposure (Jacobs et al., 2008 and Delarco et al., 2004), Neutrophils are one of the first responders of inflammatory cells to migrate towards the site of inflammation.
The neutrophils replicate during the first three stages of development, and then undergo cell differentiation.
- Myeloblast Stage:- The first stage of neutrophil development, known as the myeloblast occurs in the bone marrow.
- It is round and has large nucleus
- Containing 2 – 5 nucleoli
- There are small amount of cytoplasm which does not contain granules
- The chromatin in the nucleus is not condensed.
- Promyelocyte Stage:- This is still found in the bone marrow
- It is larger than the myeloblast
- With round or oval nucleus
- The nuclear chromatin is not condensed
- As the c ell develops the nucleoli is less prominent
- The primary granules “azurophilic” are present in the cytoplast
- The secondary granules have not developed yet
- Myelocyte Stage:-This takes place in the bone marrow, the secondary granules develop
- They glycoprotein is seen when the cell is stained
- The nucleus is round or oval, with coarse chromatin
- The nucleoli are smaller and less prominent than they are in the promyelocyte stage
- In mature neutrophils, the ratio of secondary granules to primary granules in humans is about 2-3:1.
- Metamyelocyte Stage:- The metamyelocyte are present in the blood
- The nucleus is indented and does not contain nucleoli
- The dense chromatin clumps together along the nuclear membrane
- Cytoplasm is filled with primary, secondary and tertiary granules
- Matemyelocyte stage is not capable of cell division but cell differentiation occurs.
- Polymorphonuclear Stage:- This is the last stage, band neutrophil
- Undergo further condensation of the nuclear chromatin
- The nucleus is sausage – shaped
- The nucleus has two or more lobes connected by filamentous strands
- The cytoplasm appears faintly pink due to an abundance of granules
- The fully mature neutrophils are present in the blood and tissue.