Basophils are the least common of the
granulocyteGranulocytes are a category of white blood cells characterised by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...
s, representing about 0.01% to 0.3% of circulating white blood cells.
The name comes from the fact that these leucocytes are basophilic, i.e., they are susceptible to staining by
baseIn chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. Bases are also the oxides or hydroxides of metals. A soluble base is also often referred to as an alkali if hydroxide ions are involved. This refers to the Brønsted-Lowry theory of acids and bases...
dyeA dye can generally be described as a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber....
s, as shown in the picture.
Basophils contain large
cytoplasmThe cytoplasm is the part of a cell that is enclosed within the cell membrane. In eukaryotic cells, the cytoplasm contains organelles, such as mitochondria, which are filled with liquid that is kept separate from the rest of the cytoplasm by biological membranes. The contents of the cell nucleus...
ic granules which obscure the
cell nucleusIn cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as...
under the
microscopeA microscope is an instrument to see objects too tiny for the naked eye. The science of investigating small objects using such an instrument is called microscopy. Microscopic means invisible to the eye unless aided by a microscope.-History:An early microscope was made in 1590 in Middelburg, The...
. However, when unstained, the nucleus is visible and it usually has 2 lobes. The
mast cellA mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against...
, a
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
in
tissuesTissue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function...
, has many similar characteristics. For example, both cell types store
histamineHistamine is a biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by basophils and by...
, a chemical that is secreted by the cells when stimulated in certain ways (histamine causes some of the symptoms of an
allergicAllergy is a disorder of the immune system often also referred to as atopy. Allergic reactions occur to normally harmless environmental substances known as allergens; these reactions are acquired, predictable, and rapid. Strictly, allergy is one of four forms of hypersensitivity and is called type...
reaction). Like all circulating granulocytes, basophils can be recruited out of the
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
into a tissue when needed.
Function
Basophils appear in many specific kinds of
inflammatoryInflammation is the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue. Inflammation is not a...
reactions,
particularly those that cause allergic symptoms. Basophils contain anticoagulant heparin, which prevents blood from clotting too quickly. They also contain the vasodilator histamine, which promotes blood flow to tissues. They can be found in unusually high numbers at sites of exoparasite infection, e.g.,
tickTick is the common name for the small arachnids in superfamily Ixodoidea that, along with other mites, constitute the Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and occasionally reptiles and amphibians...
s. They also appear in tissues where allergic reactions are occurring and probably contribute to the severity of these reactions. Basophils have protein receptors on their cell surface that bind IgE
antibodyAntibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses...
very tightly. It is the bound IgE antibody that confers a selective response of these cells to environmental substances, for example,
pollenPollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement between the stamens to the pistil of flowering plants or from the male cone to the...
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s. Recent studies in mice suggest that basophils may also regulate the behavior of
T cell'T cells' belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocyte types, such as B cells and natural killer cells by the presence of a special receptor on their cell surface called T cell receptors...
s and mediate the magnitude of the secondary immune response.
Secretions
When activated, basophils
degranulateDegranulation is a cellular process that releases antimicrobial cytotoxic molecules from secretory vesicles called granules found inside some cells...
to release
histamineHistamine is a biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by basophils and by...
,
proteoglycanProteoglycans are glycoproteins that are heavily glycosylated. They have a core protein with one or more covalently attached glycosaminoglycan chain. The chains are long, linear carbohydrate polymers that are negatively charged under physiological conditions, due to the occurrence of sulfate and...
s (e.g.
heparinHeparin, a highly-sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule. It can also be used to form an inner anticoagulant surface on various experimental and medical devices such as test tubes and...
and
chondroitinChondroitin is a chondrin derivative.Types include:* Chondroitin sulfate* Dermatan sulfate...
), and proteolytic enzymes (e.g.
elastaseIn molecular biology, elastase is an enzyme from the class of proteases , that break down proteins.- Forms and classification:There exist two human genes for elastase:* Pancreatic elastase * Neutrophil elastase...
and
lysophospholipaseIn enzymology, a lysophospholipase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are 2-lysophosphatidylcholine and H2O, whereas its two products are glycerophosphocholine and carboxylate....
). They also secrete
lipidLipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others...
mediators like
leukotrieneLeukotrienes are fatty molecules of the immune system that contribute to inflammation in asthma and bronchitis. Leukotriene antagonists are used to treat asthma and bronchitis....
s, and several
cytokineCytokines are any of a number of substances that are secreted by specific cells of the immune system which carry signals locally between cells, and thus have an effect on other cells. They are a category of signaling molecules that are used extensively in cellular communication. They are proteins,...
s. Histamine and proteoglycans are pre-stored in the cell's granules while the other secreted substances are newly generated. Each of these substances contributes to inflammation. Recent evidence suggests that basophils are an important source of the cytokine, interleukin-4, perhaps more important than T cells. Interleukin-4 is considered one of the critical cytokines in the development of allergies and the production of
IgEIGE is one of the largest MMORPG services companies, with offices in Los Angeles, Miami, and China. IGE is one of the main players in virtual economy services, also known in the MMORPG industry as secondary market...
antibody by the immune system. There are other substances that can activate basophils to secrete which suggests that these cells have other roles in inflammation.
BasopeniaBasopenia is a form of agranulocytosis associated with a deficiency of basophils.One cause is urticaria.It has been proposed as an indicator of ovulation....
(a low basophil count) is difficult to demonstrate as the normal basophil count is so low; it has been reported in association with autoimmune
urticariaUrticaria are a kind of skin rash notable for dark red, raised, itchy bumps. Hives are frequently caused by allergic reactions; however, there are many non-allergic causes...
(a chronic itching condition).
BasophiliaBasophilia is a condition where the basophil quantity is abnormally elevated .-Causes:...
is also uncommon but may be seen in some forms of leukaemia or
lymphomaLymphoma is a cancer that begins in the lymphocytes of the immune system and presents as a solid tumor of lymphoid cells. They often originate like balls in lymph nodes, presenting as an enlargement of the node...
.