Types of white blood cells
› Neutrophils
These cells represent 45-70% of white blood cells. They protect your body from bacteria and fungi. Also, they are the first line of defense against infection as they stimulate the other immune cells to contribute to the immune response. They are also the first cells that migrate to the site of infection. They try to kill the invader (phagocytosis) and may succeed or keep the condition under control until the body develops adaptive (specific) immunity, which is more powerful. They may undergo programmed cell death to stimulate the bone marrow to produce more neutrophils. Dead neutrophils in large numbers form what we know as pus. They have a short lifespan that ranges from 6 hours to a few days.
› Eosinophils
These cells represent 2-4% of white blood cells. They fight mainly against large parasites like hookworms and tapeworms and are responsible for the allergic response in cases of drug reactions. They are abundant in the mucosa of the respiratory and digestive tracts.
› Basophils
These cells represent 0-2% of white blood cells. They are mainly responsible for the allergic response. They produce histamine and heparin. Histamine causes vasodilation and increases the blood supply to the invaded area; it also increases the permeability of the wall of blood vessels, which enables the neutrophils and other immune cells to reach the tissues. Heparin inhibits blood clotting, which improves the blood flow carrying the immune cells to the injured area. They also send signals that attract neutrophils and eosinophils to the site of infection.
› Monocytes
These cells represent 4-8% of white blood cells, and they are the largest of them. They help the neutrophils in their function (killing the invaders or phagocytosis), but perform other functions as well:
✦ They introduce the harmful organisms to the T-lymphocytes that recognize and kill them (Antigen-presenting cells).
✦ They also leave blood into tissues to become tissue macrophages. Tissue macrophages kill the infected cells (such as viral-infected cells), clean the dead cells, and attack the foreign and harmful organisms.
› Lymphocytes
These cells represent 25-40% of white blood cells. There are two subtypes of lymphocytes:
♦ T-lymphocytes: These cells recognize the infected cells -either viral or bacterial infected cells- and kill them. Also, they have a memory that saves the antigen, which enables them to respond rapidly if the same infection occurred again. Additionally, they can identify and kill tumor cells.
♦ B-lymphocytes: These cells don’t kill the antigens directly, but they produce proteins called antibodies. Antibodies bind to the surface of antigen, which prevents its harmful action and help the other immune cells to recognize and kill the pathogen.
The normal white blood cell count
We should know the normal white blood cell count and each type count, because any abnormal increase or decrease may indicate a problem.
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- Total white blood cell count: 4000-11000 cell/mm3
- Neutrophils: 3000-7000 cell/mm3 (45-70%)
- Esinophils: 50-400 cell/mm3 (2-4%)
- Basophils: 0-100 cell/mm3 (0-2%)
- Monocytes: 400-800 cell/mm3 (4-8%)
- Lymphocytes: 1700-3400 cell/mm3 (25-40%)
High white blood cell count means leukocytosis while low white blood cell count means leukopenia, and we will discuss each of them.
⇒ Now, let’s discuss high white blood cell count (leukocytosis).
