Leukocytes, or white blood cells, are vital to the body’s ability to fight off infection and promote healing. There are five types of leukocytes, each with distinct morphologies and functions. According to Gary Thibodeau, PhD, and Kevin Patton, PhD, authors of “The Human Body in Health and Disease,” abnormal leukocyte levels can indicate serious health problems.
Granular vs. Nongranular Cytoplasm
The five types of leukocytes are divided into two categories: granulocytes and nongranulocytes. Neutrophils, eosinophils and basophils are granulocytes. These contain visible granules in their cytoplasm when stained and observed under a microscope. Nongranulocytes include lymphocytes and monocytes. These leukocytes display no granules in their cytoplasm.
Single vs. Multilobed Nuclei
Thibodeau and Patton explain that granulocytes have multilobed nuclei. The configuration of these lobes varies with the type of granulocyte. Neutrophils are described as having up to three or more lobes. Eosinophils and basophils typically have two lobes to each nucleus. Agranulocytes are single-lobed. Lymphocytes typically have a single large, round nucleus. Monocyte nuclei are single lobed and shaped like a kidney.
Phagocytosis vs. Antibody Production
Phagocytosis and antibody production are two methods by which leukocytes aid the immune system in fighting off infectious agents and other foreign bodies. Phagocytosis is a process wherein a leukocyte engulfs and digests microorganisms, irritants, or cancer cells that threaten the body. Neutrophils are particularly adept in the phagocytosis of small microorganisms. Thibodeau and Patton explain that eosinophils attack and digest larger invaders, such as parasitic worms and protozoa. Monocytes use phagocytosis to ingest cellular debris and cancer cells.
Antibody production is another function of leukocytes. This process is vital in addressing the threat of repeat infections. Antibodies are produced by lymphocytes in response to the presence of a foreign invader, known as an antigen. Subsequent exposure to the antigen will prompt the release of antibodies that bind to the antigen, killing it, or rendering it vulnerable to phagocytosis.
Lymphoid vs. Myeloid Differentiation
All blood cells originate as stem cells known as hemocytoblasts. Beyond this initial stage, the hemocytoblast may differentiate into a granulocyte or a nongranulocyte depending on whether it originates in lymphoid or myeloid tissue, explains Cheryl Davis, PhD, of the Biology and Biotechnology Center at Western Kentucky University. White blood cells that form in the lymph glands differentiate from stem cells into either lymphocytes or monocytes. Those that form in the bone marrow, or myeloid tissue, become neutrophils, eosinophils or basophils.
- The Human Body in Health and Disease; Gary Thibodeau, PhD, and Kevin Patton, PhD; 2002
- RnCeus.com: White Blood Cell Count (WBC) and Differential