White Blood Cells (WBC)

White blood cells, also known as leukocytes, are colorless immune system cells that lack pigment. They are produced in the bone marrow. Unlike red blood cells and platelets, white blood cells contain a nucleus.

Leukocytes protect against pathogens such as bacteria and aid in tissue repair as part of the immune system. The different types of white blood cells include neutrophils, eosinophils, basophils, lymphocytes, and monocytes. White blood cells (leukocytes) are found in the blood, lymphatic fluid, and tissues throughout the body.

The number of white blood cells is an important indicator, particularly in infectious diseases. Therefore, the WBC count is a significant parameter in a complete blood count. The normal range for the white blood cell count is between 4,000 and 10,000/mm3. Leukocytes constitute approximately 1% of the total blood volume of a healthy adult (the red blood cell ratio is 40-45%).

An increase in the white blood cell count above the upper limit is termed leukocytosis, whereas a decrease below the lower limit is termed leukopenia.

Classification of White Blood Cells

• Myeloid Series (granulocytes or polymorphonuclear cells ( PMNs))
  • Neutrophil (62%)
  • Eosinophil (2.3%)
  • Basophil (0.4%)
• Lymphoid Series (agranulocytes)
  • Lymphocyte (30%)
    • B lymphocyte
    • T lymphocyte
    • NK cells
  • Monocyte (5.3%)
  • Macrophage

Neutrophils, monocytes, and macrophages are phagocytic cells.

Monocytes are the largest type of white blood cells, and they are capable of differentiating into macrophages.

Neutrophils are the most abundant type of white blood cell (40-75%) and the most abundant granulocyte. They are short-lived and highly mobile. Neutrophils are phagocytes that are typically found in the bloodstream. Neutrophils are the first cells to arrive at the inflammatory site during the onset of inflammation (particularly bacterial infection, environmental factors, and certain cancers); their presence in the tissue is one of the characteristics of acute inflammation.

Eosinophils (also known as acidophils) combat multicellular parasites and other infections, as well as play a role in allergic reactions and asthma.

Basophils are the largest type of granulocyte. They are responsible for the development of acute and chronic allergic diseases, including anaphylaxis, asthma, atopic dermatitis, and hay fever, as well as inflammatory immune responses. They can produce histamine and serotonin, which trigger inflammation, and heparin, which prevents blood clotting.

Lymphocytes include NK cells (cell-mediated, cytotoxic, innate immunity), T cells (cell-mediated cytotoxic, adaptive immunity), and B cells (humoral, antibody-mediated adaptive immunity). The lymphocytes are found in lymphoid tissue.

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