What are White Blood Cells/Leukocytes?
White blood cells (WBC), or leukocytes are important components of our blood system. The scientific name ‘leukocyte’ is derived from the Greek origin, leuko- denotes ‘white’ and cyte meaning ‘cell’. ‘white blood cell’ reflects the physical appearance of blood sample after centrifugation as shown below in Fig.1. They are made in the bone marrow and very crucial for us to have a good health and protecting the body against infection and disease; this can be from germs, viruses, or other external substances that the body sees as threat. White blood cells are endlessly produced in the bone marrow and kept ready within the blood and lymphatic systems until they are needed. Leukocytes are much less than red blood cells and account for about 1% of the cells in blood.
‘blood-centrifuge-buffy-coat-erythrocytes-hematocrit’ by Ron Mao CC All rights reserved
Complete Blood Count (CBC): is a blood test or full blood count/exam performed for a variety of reasons: to evaluate overall health, to diagnose medical condition, to monitor a medical condition, and to monitor medical treatment. CBC test measures several components and features of our blood:
. Red blood cells — carry oxygen
. White blood cells — fight infection
. Hemoglobin — the oxygen-carrying protein in red blood cells
. Hematocrit — the proportion of red blood cells to the fluid component, or plasma, in our blood
. Platelets — help with blood clotting
From the above cellular components of blood, this article focusses only on WBCs. There are five major types of leukocytes, and these are divided into two different groups, named for their appearance under a microscope.
Granulocytes: includes neutrophils, eosinophils, and basophils, which have granules in their cytoplasm when stained and viewed on a microscope.
Agranulocytes: consist of monocytes and lymphocytes, which do not have granules in the cytoplasm, they are also known mononuclear cells.
Fig. 2. WBCs stained and viewed under microscope — Source: Healthmatters.io (copyright): https://blog.healthmatters.io/2017/05/15/what-are-white-blood-cells/
Neutrophils: are the most abundant type of leukocytes (40% — 75%) and the most abundant type of granulocytes. Their function is to fight infection by ingesting microorganism and releasing enzymes that kill the microorganisms.
Eosinophils: are one type granulocytes, account for less than 7% of white blood cells. Their function is to attack and kill parasites, destroy cancer cells, and they are part of allergic responses.
Basophils: are created in response to inflammation and infection like other leukocytes, comprising a small percentage of the total white blood cells circulating in the blood (0.4% — 1%). They secrete chemicals such as histamine, a marker of allergic disease which can induce inflammation in response to an allergen. Basophils also excrete heparin that is used to prevent blood from clotting too quickly.
Monocytes: are a larger than other leukocytes but only account for 2% — 8% of the total white blood cells in circulation. They are responsible for attacking and breaking down germs or bacteria that enter a person’s body. When they are needed, monocytes travel to other organs, such as the spleen, liver, lungs, and bone marrow, where they transform into a cell called a macrophage. A macrophage is responsible for many cellular functions, including removing dead or damaged tissue, destroying cancer cells, and regulating the immune response.
Lymphocytes: are the major component of our body’s adaptive immune response and usually account for approximately 20–40% of the total white blood cells. They act by identifying foreign objects, like bacteria and viruses, and generating a specific response that is made for the invader. Lymphocytes have three major types: T cells, B cells, and Natural Killer cells.