What Are White Blood Cells? What Do They Do?

White Blood Cells are part of the blood, which are an important constituent of our immune system. The role of these cells which circulate in our blood stream is to fight and destroy the parasites, viruses and other foreign particles which can pose a threat to the body. These cells are known by many names among which Leukocytes and WBCs are the most popular ones among doctors. The white blood cells are of many different types each having its own particular purpose in the body. The two major categories in which you can divide the WBCs are granulocytes and agranulocytes.



Granulocytes are the most common type of white blood cells present in the human body which account for almost 70 -75 percent of the WBCs. The reason for such a name of these cells is because they contain small and visible granules within their cytoplasm. The visibility of these granules can be attained by staining. The life cycle of these cells is not that much and they have to be replaced every 12 hours. The granulocytes are subdivided further in to three sub-categories which are:

1. Neutrophils

The neutrophils are the most abundant type of granulocytes. Almost 65 percent of all the white blood cells found in our blood are neutrophils. These are the cells that are tasked with the duty of responding to any fungal or bacterial invasion. In essence they are the first line to defense our immune system and are the first ones to respond when a bacteria or fungus tries to attack the body. These cells also referred to as PMN or polymorphonuclear leukocytes are found in pus and usually involved in any inflammation process taking place anywhere in the body. Elevated levels of this cell are a common indication of the presence of an infection in the body since their production increase whenever an infection invades the body.

2. Basophils

Basophils are a type of granulocytes that are found in a very low quantity in the body. Although these cells only account for about 1 percent of the WBCs, they are equally important for the immune system. They have the responsibility of secreting a chemical known by the name of histamine whenever the body encounters an infection. This chemical initiates the inflammatory reaction and is also used in a number of other processes going on in the body.

3. Eosinophils

Eosinophils make up about 4 percent of the leukocytes found in our bodies. These cells are tasked with the duty of fighting off parasites and infections that cause allergies. You are bound to have elevated levels of Eosinophils in your body if you are suffering from allergy induced asthma or hives.


In contrast to the granulocytes, the agranulocytes do not have any type of granules in their cytoplasm. They also do not have any membrane covering that is the characteristic feature of the granulocytes. The agranulocytes are subdivided further into two subcategories which are:

1. Lymphocytes

Lymphocytes are the most abundant type of agranulocytes found in our bodies and account for about 25 percent of our white blood cells. There is no single type of these cells and there are as many as three separate types of Lymphocytes which are named B cells, T cells and NK cells.

  • The B cells are antibody producers and their main task is to generate antibodies whenever an infection invades the body. These antibodies are produced for the sole purpose of destroying the foreign particle that has entered the blood stream. Their mode of operation involves clinging to the cells of the bacteria and then launching a series of reactions that tear it apart and help the body in killing it.
  • The T cells are also divided in two types which are named CD4 and CD8 respectively. The CD4 T cells perform the task of coordinating with the other cells in the destruction of the foreign bodies attacking the body. They can be considered as the facilitators which provide the platform for the killing cells and antibodies to perform their task more effectively. The CD8 T cells on the other hand are destroyers and can be considered as the soldiers which march in to battle and defeat the enemy cells.
  • The NK cells or Natural Killer cells are a special type of lymphocytes which are tasked with the duty similar to that of the CD8 T cells, which is to annihilate their targets. The difference between CD8 T cells and NK cells is that the latter do not need activation for killing the invaders.

2. Monocytes

The Monocytes are a unique type of agranulocytes that have a very peculiar task to perform in our body’s immune system. These cells have a much larger life span than the other WBCs and have the duty to patrol every inch of the body and search for waste particles and other bacteria that have not yet been removed from the blood stream. When the monocytes find such a particle they consume it and break it down in to small bits. They display these bits on their surfaces to warn the T cells of their presence and help them in understanding their chemical nature so that if more of these particles invade the body in future, the T cells can eliminate them with ease.

Macrophages are an enhanced form of Monocytes that have a similar type of function as them. The transformation of a monocyte into a macrophage occurs when it leaves the blood stream and enters the tissues in the body.