| Basophil | |
|---|---|
.png) 3D rendering of a basophil | |
 Dyed basophil among red blood cells | |
| Details | |
| System | Immune system |
| Identifiers | |
| MeSH | D001491 |
| TH | H2.00.04.1.02022 |
| FMA | 62862 |
| Anatomical terms of microanatomy | |
Basophils are a type ofwhite blood cell. Basophils are the least common type ofgranulocyte, representing about 0.5% to 1% of circulatingwhite blood cells.[1] They are the largest type of granulocyte. They are responsible for inflammatory reactions during immune response, as well as in the formation of acute and chronic allergic diseases, includinganaphylaxis,asthma,atopic dermatitis andhay fever.[2] They also produce compounds that coordinate immune responses, includinghistamine andserotonin that induce inflammation, andheparin that preventsblood clotting,[3] although there are less than that found inmast cell granules.[4] Mast cells were once thought to be basophils that migrated from the blood into their resident tissues (connective tissue), but they are now known to be different types of cells.[5]
Basophils were discovered in 1879 by German physicianPaul Ehrlich, who one year earlier had found a cell type present in tissues that he termedmastzellen (now mast cells).[6] Ehrlich received the 1908 Nobel Prize in Physiology or Medicine for his discoveries.
The name comes from the fact that these leukocytes are basophilic, i.e., they are susceptible tostaining bybasicdyes, as shown in the picture.
Basophils contain largecytoplasmic granules which obscure thecell nucleus under themicroscope when stained. However, when unstained, the nucleus is visible and it usually has twolobes.[7] Themast cell, another granulocyte, is similar in appearance and function. Both cell types storehistamine, a chemical that is secreted by the cells when stimulated. However, they arise from different branches ofhematopoiesis, 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 theblood into a tissue when needed.
Basophils appear in many specific kinds ofinflammatory reactions, particularly those that causeallergic symptoms. Basophils contain anticoagulantheparin,[8] which prevents blood from clotting too quickly. They also contain the vasodilatorhistamine, which promotes blood flow to tissues. They can be found in unusually high numbers at sites ofectoparasite infection (e.g.,ticks).
Likeeosinophils, basophils play a role in both parasitic infections and allergies.[9] They are found 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 bindIgE, animmunoglobulin involved in macroparasite defense andallergy. It is the bound IgE antibody that confers a selective response of these cells to environmental substances (e.g.,pollen proteins orhelminth antigens).
Recent studies in mice suggest that basophils may also regulate the behavior ofT cells and mediate the magnitude of the secondary immune response.[10]
Basophil function is inhibited byCD200.Herpesvirus-6, herpesvirus-7, and herpesvirus-8 produce a CD200homolog which also inhibits basophil function. This suggests that basophils may play a role in the immune response to these viruses.[11] 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.[12]
Basophils arise and mature inbone marrow. When activated, basophilsdegranulate to releasehistamine,proteoglycans (e.g.heparin andchondroitin), andproteolytic enzymes (e.g.elastase andlysophospholipase). They also secretelipid mediators likeleukotrienes (LTD-4), and severalcytokines. 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 thecytokine,interleukin-4, perhaps more important thanT cells. Interleukin-4 is considered one of the critical cytokines in the development of allergies and the production ofIgE 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.[13]
The degranulation of basophils can be investigatedin vitro by usingflow cytometry and the so-called basophil-activation-test (BAT). Especially, in the diagnosis of allergies including of drug reactions (e.g. induced bycontrast medium), the BAT is of great impact.[14]
Basopenia (a low basophil count) is difficult to demonstrate as the normal basophil count is so low; it has been reported in association with autoimmuneurticaria[15] (a chronic itching condition).Basophilia is also uncommon but may be seen in some forms ofleukemia orlymphoma.
Basophils of mice and humans have consistent immunophenotypes, includingFcεRI+,CD123,CD49b(DX-5)+,CD69+,Thy-1.2+,2B4+,CD11bdull,CD117(c-kit)−,CD24−,CD19−,CD80−,CD14−,CD23−,Ly49c−,CD122−,CD11c−, Gr-1−, NK1.1−,B220−,CD3−, γδTCR−, αβTCR−, α4 and β4-integrin negative.[16]
Recently, Heneberg[17] proposed that basophils may be defined as the cellular population positive forCD13,CD44,CD54,CD63,CD69,CD107a,CD123,CD164,CD193/CCR3,CD203c,TLR-4, andFcεRI. When activated, some additional surface markers are known to be upregulated (CD13, CD107a, CD164), or surface-exposed (CD63, and theectoenzyme CD203c).[17]
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.[18] 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 successfulallergen immunotherapy (desensitization) to differentiate short-term desensitization versus sustained unresponsiveness to the allergen.[19]
The wordbasophil usescombining forms ofbaso- +-phil, yielding "base-loving".
