Bursa of Fabricius
In bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, the bursa of Fabricius (Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

: Bursa cloacalis or Bursa fabricii) is the site of hematopoiesis, a specialized organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...

 that, as first demonstrated by Bruce Glick and later by Max Cooper and Robert Good, is necessary for B cell
B cell
B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...

 (part of the immune system) development in birds. Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s generally do not have an equivalent organ; the bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

 is often both the site of hematopoiesis and B cell development.
it is present in cloaca of birds
It is named after Hieronymus Fabricius
Hieronymus Fabricius
Hieronymus Fabricius or Girolamo Fabrizio or by his Latin name Fabricus ab Aquapendende also Girolamo Fabrizi d'Acquapendente was a pioneering anatomist and surgeon known in medical science as "The Father of Embryology."...

 who described it in 1621.


The bursa is an epithelial
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...

 and lymphoid organ that is found only in birds. The bursa develops as a Dorsal diverticulum of the proctadael region of the cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...

. The luminal
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...

 (interior) surface of the bursa is plicated with as many as 15 primary and 7 secondary plicae or folds. These plicae have hundreds of bursal follicles containing follicle-associated epithelial cells, lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

s, macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

s, and plasma cells. Lymphoid stem cells migrate from the fetal liver to the bursa during ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...

. In the bursa, these stem cells acquire the characteristics of mature, immunocompetent B cells.

The bursa is active in young birds. It atrophies after about six months.

Origin of the Name 'B Cells'

The ‘B’ in ‘B cell’ refers to bursa-derived. This is simply because during the 1960s B cells were first defined (and distinguished from thymus-derived T cells) in birds, which have a bursa. A decade later, after examining almost every other organ including the appendix, researchers finally discovered that mammalian B cells develop in the bone marrow and spleen. The fact that ‘bone marrow’, like bursa, starts with a ‘B’ is sheer coincidence.

Research history

In 1956, Bruce Glick showed that removal of the bursa in newly hatched chicks severely impaired the ability of the adult birds to produce antibodies. In contrast, removal of the bursa in adult chickens has not much effect on the immune system. This was a serendipitous discovery that came about when a fellow graduate, Timothy S. Chang, who was teaching a course on antibody production obtained chickens from Glick that had been bursectomised (removal of the bursa). When these chickens failed to produce antibody in response to an immunization with Staphylococcus
Staphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....

 bacteria, the two students realized that the bursa is necessary for antibody production. Their initial attempts to publish their findings were thwarted by an editor who commented that "further elucidation of the mechanism ... should be attempted before publication.”

The role of the thymus
The thymus is a specialized organ of the immune system. The thymus produces and "educates" T-lymphocytes , which are critical cells of the adaptive immune system....

 in the immune response was also identified shortly after the discovery of bursa’s role in antibody responses. In thymectomized animals, the ability to reject allografts, and to mount delayed hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...

 responses, was drastically reduced. By the mid-1960s, immunologists were convinced that there were indeed two separate arms of the immune system: one dealing exclusively with the production of circulating antibodies (humoral immunity
Humoral immunity
The Humoral Immune Response is the aspect of immunity that is mediated by secreted antibodies produced in the cells of the B lymphocyte lineage . B Cells transform into plasma cells which secrete antibodies...

), and another that is involved in the delayed hypersensitivity-type reactions and graft rejections (cell-mediated immunity
Cell-mediated immunity
Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells , antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen...



Infectious Bursal Disease
Infectious Bursal Disease
Infectious bursal disease is a highly contagious disease of young chickens caused by infectious bursal disease virus , characterized by immunosuppression and mortality generally at 3 to 6 weeks of age. The disease was first discovered in Gumboro, Delaware in 1962...

(IBD) is a viral disease in poultry. Typically, the virus attacks the Bursa of young birds, preventing development of the immune system.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.