A basophil has large granules that stain dark blue to purple and a two-lobed nucleus. The most common of all the leukocytes, neutrophils will normally comprise 50—70 percent of total leukocyte count. They are called neutrophils because their granules show up most clearly with stains that are chemically neutral neither acidic nor basic.
The granules are numerous but quite fine and normally appear light lilac. The nucleus has a distinct lobed appearance and may have two to five lobes, the number increasing with the age of the cell. Neutrophils are rapid responders to the site of infection and are efficient phagocytes with a preference for bacteria. Their granules include lysozyme , an enzyme capable of lysing, or breaking down, bacterial cell walls; oxidants such as hydrogen peroxide; and defensins , proteins that bind to and puncture bacterial and fungal plasma membranes, so that the cell contents leak out.
A burn injury increases the proliferation of neutrophils in order to fight off infection that can result from the destruction of the barrier of the skin.
Eosinophils typically represent 2—4 percent of total leukocyte count. The granules of eosinophils stain best with an acidic stain known as eosin. The nucleus of the eosinophil will typically have two to three lobes and, if stained properly, the granules will have a distinct red to orange color.
The granules of eosinophils include antihistamine molecules, which counteract the activities of histamines, inflammatory chemicals produced by basophils and mast cells.
Some eosinophil granules contain molecules toxic to parasitic worms, which can enter the body through the integument, or when an individual consumes raw or undercooked fish or meat. Eosinophils are also capable of phagocytosis and are particularly effective when antibodies bind to the target and form an antigen-antibody complex. High counts of eosinophils are typical of patients experiencing allergies, parasitic worm infestations, and some autoimmune diseases.
Low counts may be due to drug toxicity and stress. Basophils are the least common leukocytes, typically comprising less than one percent of the total leukocyte count. The granules of basophils stain best with basic alkaline stains. Basophils contain large granules that pick up a dark blue stain and are so common they may make it difficult to see the two-lobed nucleus. In general, basophils intensify the inflammatory response.
They share this trait with mast cells. In the past, mast cells were considered to be basophils that left the circulation. However, this appears not to be the case, as the two cell types develop from different lineages. The granules of basophils release histamines, which contribute to inflammation, and heparin, which opposes blood clotting. High counts of basophils are associated with allergies, parasitic infections, and hypothyroidism.
Low counts are associated with pregnancy, stress, and hyperthyroidism. Agranular leukocytes contain smaller, less-visible granules in their cytoplasm than do granular leukocytes. The nucleus is simple in shape, sometimes with an indentation but without distinct lobes. There are two major types of agranulocytes: lymphocytes and monocytes see Figure 1 in Production of the Formed Elements.
Lymphocytes are the only formed element of blood that arises from lymphoid stem cells. Although they form initially in the bone marrow, much of their subsequent development and reproduction occurs in the lymphatic tissues. Lymphocytes are the second most common type of leukocyte, accounting for about 20—30 percent of all leukocytes, and are essential for the immune response.
The size range of lymphocytes is quite extensive, with some authorities recognizing two size classes and others three. This finding has led to the three size range classification. The three major groups of lymphocytes include natural killer cells, B cells, and T cells.
Thus, they provide generalized, nonspecific immunity. The larger lymphocytes are typically NK cells. B cells and T cells, also called B lymphocytes and T lymphocytes , play prominent roles in defending the body against specific pathogens disease-causing microorganisms and are involved in specific immunity. One form of B cells plasma cells produces the antibodies or immunoglobulins that bind to specific foreign or abnormal components of plasma membranes.
Most leukocytes spend a short time circulating in the blood, and the rest of the time, they can be found within lymphatic tissues or organs like the thymus or spleen. They are often secretory vessels. The different types of granular myeloid white blood cells —neutrophils, basophils, and eosinophils—are named based on the type of stain that makes their granules most visible. Each type of granular myeloid white blood cell has granules with different chemical contents that help these cells respond to different types of pathogens.
Neutrophils are the most numerous granulocytes, making up a large percentage of the leukocytes found in human blood. In neutrophils, the granules are small and evenly distributed, and they appear pale lilac in color when they absorb basic or acidic dyes. Like other granulocytes, the nuclei of neutrophils are segmented into several connected sections, or lobes. Because of this, granulocytes are often referred to as polymorphonuclear leukocytes PMNs.
Most neutrophils have between two and five lobes that vary in shape. Neutrophils play a significant role in the innate immune response, often being the first, and most numerous, type of white blood cell to arrive at sites of infection or inflammation. They are phagocytes , meaning they engulf and destroy pathogens via a process called phagocytosis.
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NCI Grant Policies. Types of WBCs The different types of white blood cells leukocytes include neutrophils, basophils, eosinophils, lymphocytes, monocytes, and macrophages. Learning Objectives Distinguish between the two major types of leukocytes white blood cells : granulocytes and agranulocytes. Key Takeaways Key Points The two main types of leukocytes are granulocytes and mononuclear leukocytes agranulocytes.
Leukocytes arise from hemopoietic stem cells in the bone marrow. Leukocytes are involved in pathogen recognition, phagocytosis ingestion of particles , pathogen destruction, inflammation mediation, and antigen presentation.
Granulocytes include neutrophils, basophils, eosinophils, and mast cells. Their granules contain enzymes that damage or digest pathogens and release inflammatory mediators into the bloodstream. Mononuclear leukocytes include lymphocytes, monocytes, macrophages, and dendritic cells. This group is involved in both innate and adaptive immune system function.
Key Terms endocytosed : Engulfed during the process by which the plasma membrane of a cell folds inwards to ingest material. Examples include bacteria, viruses, protozoa, or fungi. Microorganisms are not considered pathogenic until the population has grown large enough to cause disease.
Learning Objectives Describe the functions of leukocytes white blood cells. Key Takeaways Key Points Leukocyte functions often occur in the bloodstream and may represent either the innate or adaptive immune systems. Innate immune system functions are non-specific and include phagocytosis, inflammation, and degranulation. Adaptive immune system functions are antigen -specific and involve antigen presentation as well as cell -mediated and humoral -mediated activities.
Compared to innate immune system functions, adaptive immune system functions take more time to initiate, but work much faster. They have a memory component to prevent reinfection by the same pathogen. Key Terms macrophage : A white blood cell that phagocytizes necrotic cell debris and foreign material, including viruses, bacteria, and tattoo ink.
Part of the innate immune system. Inflammation : An innate immune system function in response to a pathogen or injury. Chemical mediators cause the blood vessels to dilate and become more permeable, which draws neutrophils to the area.
WBC Formation Haematopoiesis refers to the formation of blood cells components.
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