White Blood Cells

White blood cells (WBC) also known as leukocytes are a type of cells that are found in the blood. Their main function is to fight infection. They are the soldiers and guard the body against any intruders. As soon as bacteria, viruses, or other microorganisms enter the body, they arrive to fight them and prevent spread of infection. They are produced in the bone marrow from stem cells and are classified into two groups.


Granular leukocytes (Granulocytes) – are formed in the bone marrow and account for 70% of all white blood cells. There are 3 types of granulocytes:(2)

1. Neutrophils - are the most common type and compose about 50 to 70% of all WBCs. They are phagocytic which means they can ingest other cells and they are the first to arrive to the infection site.(1)

2. Eosinophils – they move around by eating some types of bacteria, foreign micro organisms, and other cells. They also defend the body against parasites.(5)

3. Basophils – they are the smallest granulocytes and have the least known function.(4) They play a part in allergic responses.(1)

Non-granular leukocytes (agranulocytes) – There are two types:
1. Monocytes – when they move to an area of infection, they are transformed into macrophages which are large phagocytic cells that trap and destroy organisms left behind by granulocytes and lymphocytes. (2)

2. Lymphocytes – this type of leukocyte proliferates (multiply) rapidly when an infection is present and there are two types; B lymphocytes and T lymphocytes.(2)