Basophils are a type of white blood cell. Basophils are the least common type of granulocyte, representing about 0.5% to 1% of circulating white blood cells.
Basophils were discovered in 1879 by German physician Paul Ehrlich, who one year earlier had found a cell type present in tissues that he termed mastzellen (now mast cells).
The name comes from the fact that these leukocytes are basophilic, i.e., they are susceptible to staining by basic , as shown in the picture.
Structure
Basophils contain large
granules which obscure the
cell nucleus under the
microscope when stained. However, when unstained, the nucleus is visible and it usually has two
Lobation.
The
mast cell, another granulocyte, is similar in appearance and function. Both cell types store
histamine, a chemical that is secreted by the cells when stimulated. However, they arise from different branches of
hematopoiesis, and mast cells usually do not circulate in the blood stream, but instead are located in connective tissue. Like all circulating granulocytes, basophils can be recruited out of the
blood into a tissue when needed.
Function
Basophils appear in many specific kinds of
inflammation reactions, particularly those that cause
allergy 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
ectoparasite infection (e.g.,
).
Like eosinophils, basophils play a role in both parasitic infections and allergies.
Recent studies in mice suggest that basophils may also regulate the behavior of and mediate the magnitude of the secondary immune response.
CD200
Basophil function is inhibited by CD200. Herpesvirus-6, herpesvirus-7, and herpesvirus-8 produce a CD200 homolog which also inhibits basophil function. This suggests that basophils may play a role in the immune response to these viruses.
The role of basophils in the immune response to these viruses is further supported by findings that the CD200 receptor is expressed more frequently in basophils than in other circulating leukocytes.
Secretions
Basophils arise and mature in
bone marrow. When activated, basophils
degranulation to release
histamine,
(e.g.
heparin and
chondroitin), and proteolytic enzymes (e.g.
elastase and lysophospholipase). They also secrete
lipid mediators like
(LTD-4), and several
. 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
IgE 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.
The degranulation of basophils can be investigated in vitro by using flow cytometry and the so-called basophil-activation-test (BAT). Especially, in the diagnosis of allergies including of drug reactions (e.g. induced by contrast medium), the BAT is of great impact.
Basopenia (a low basophil count) is difficult to demonstrate as the normal basophil count is so low; it has been reported in association with autoimmune urticaria
Clinical significance
Immunophenotyping
Basophils of mice and humans have consistent immunophenotypes, including FcεRI
+, CD123, CD49b(DX-5)
+, CD69
+, Thy-1.2
+, 2B4
+, CD11b
dull, CD117(c-kit)
−, CD24
−, CD19
−, CD80
−, CD14
−, CD23
−, Ly49c
−, CD122
−, CD11c
−, Gr-1
−, NK1.1
−, B220
−, CD3
−, γδ
T-cell receptor−, αβ
T-cell receptor−, α
4 and β
4-
integrin negative.
Recently, Heneberg
Allergy diagnosis
Basophils are easily isolated from venous blood and present good "indicator cells" of an IgE-mediated allergic response based on the upregulation of activation markers such as CD63 and/or CD203c upon suspect allergen stimulation.
Therefore, the BAT serves to confirm IgE-mediated allergy following uncertain results from classical testing based on anamnesis, skin testing or specific IgE results. More recently, BAT has also been used for the monitoring of successful allergen immunotherapy (desensitization) to differentiate short-term desensitization versus sustained unresponsiveness to the allergen.
Etymology and pronunciation
The word
basophil uses combining forms of
+ , yielding "base-loving".
==Additional images==
See also
External links
