White blood cells (WBCs), also known as leukocytes, are the blood cells that are considered an integral part of the immune system. They are concerned with protecting the body from foreign infectious agents like bacteria and viruses.
WBCs are produced by the cells of the bone marrow. The normal white blood cell count in a healthy adult should be 4,000 to 10,000 cells per microliter of blood. There are basically five types of leukocytes. Here is a brief discussion about the various types of WBCs and their functions.
Types of Leukocytes and Their Functions
There are basically five types of WBCs, which are known as neutrophils, basophils, eosinophils, monocytes, and lymphocytes. They are generally classified into two categories - granulocytes and agranulocytes. Granulocytes are those leukocytes that contain granules in their cytoplasm, while agranulocytes are characterized by the absence of such granules.
A neutrophil is usually about 10 to 12 micrometer in diameter with a multilobed nucleus, for which it is also known as the 'polymorphonuclear leukocyte'. Neutrophils are characterized by the presence of granules in their cytoplasm, and they are mainly concerned with protecting the body from bacterial and fungal infections. Neutrophils can kill bacteria by directly ingesting them, which is known as phagocytosis. Neutrophils account for almost 60 to 70% of total leukocyte count, and their lifespan is about 6 hours to a few days.
Eosinophils are mainly known for their role in allergic reactions. They have bilobed nuclei, and their diameter is usually 10 to 12 micrometer. An increase in the number of eosinophils is usually associated with allergies, asthma, and hay fever. Eosinophils are also responsible for fighting parasitic infections, and hence such infections can cause the number of eosinophils to increase in the body. The average life span of a eosinophil is about 8 to 12 days.
Basophils are another type of granulocytes that are associated with allergic reactions. These cells have bi or trilobed nuclei. They contain large and coarse, blue-colored granules in their cytoplasm. They release the chemical histamine during an allergic reaction, which produces the typical signs and symptoms associated with allergies. The diameter of a basophil can be approximately 12 to 15 micrometer.
Monocytes are agranulocytes, and they are concerned with phagocytosis, just like neutrophils. However, they live longer than neutrophils. Monocytes can leave the bloodstream and enter the body tissues, where they can undergo some changes and turn into macrophages. As tissue macrophages, monocytes destroy and remove dead, old, and damaged cells from the body.
An interesting finding about monocytes is that they can replace their lysosomal content. Monocytes possess kidney-shaped nuclei, and their diameter is usually 14 to 17 micrometer. Monocytes present the fragments of a pathogen to T-lymphocytes, so that the T-lymphocytes can recognize the pathogen in future. Monocytes remain in the bloodstream for 10 to 20 hours, after which they enter the tissues and live there for several days.
Lymphocytes differ from the other types of white blood cells by the fact that they can recognize the invading pathogens. There are several types of lymphocytes, such as B lymphocytes, helper T cells, cytotoxic T cells, memory T cells, and suppressor or regulatory T cells. B lymphocytes are concerned with the production of antibodies, while helper T cells activate and direct the immune system. Cytotoxic T cells are responsible for releasing chemicals that can destroy the invading pathogens. Memory T cells on the other hand, help the immune system recognize the particular pathogen, if it again enters the body. Regulatory T cells are responsible for suppressing the immune response when it is no longer required, and thus they help protect the normal cells of the body.
The normal white blood cell count is 4,000 to 10,000 cells per microliter of blood. If the number of leukocytes increases in the body over the upper limit, the condition is referred to as leukocytosis, which usually indicates the presence of an infection in the body. The elevated count of WBCs in the body can also be associated with diseases of the bone marrow, drug reactions, and immune system disorders.
Leukopenia is the term used for a low leukocyte count. Leukopenia can be caused by several factors, of which viral infections are worth mentioning. Viral infections can disturb the functions of the bone marrow temporarily to cause leukopenia. Apart from Infections, this condition can be associated with the intake of certain drugs, diseases of the liver or spleen, and the destruction of the bone marrow cells, which can be caused by certain types of cancer. However, it is possible to increase the count of leukocytes with a proper diet and a healthy lifestyle, if it is not caused by a serious health problem.
Sometimes, leukocytes can be found in urine and stool as well, which can be an indicator of certain illnesses. The presence of a high level of leukocytes in the urine can be a sign of infections, especially infections of the urinary tract, bladder, or the kidneys. On the other hand, the presence of leukocytes in stool can be caused by conditions like diarrhea and infections of the intestinal tract.