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ursa of Fabricius 118 butterfly rash
Frank Macfarlane Burnet.
Fenner’s suggested explanation of immunologic tolerance
was tested by Medawar et al., who confirmed the hypothesis
in 1953 using inbred strains of mice. (Refer to Production
of Antibodies [with Fenner], 1949; Natural History of
Infectious Diseases, 1953; Clonal Selection Theory of
Antibody Formation, 1959; Autoimmune Diseases [with
Mackay], 1962; Cellular Immunology, 1969; Changing
Patterns [autobiography], 1969.)
Bursa fabricius
Bursa of Fabricius.
bursa of Fabricius
An outpouching of the hindgut located near the cloaca in
avian species that governs B cell ontogeny. This specific
lymphoid organ is the site of migration and maturation
of B lymphocytes. The bursa is located near the terminal
portion of the cloaca and, like the thymus, is a lymphoepithelial
organ. The bursa begins to develop after the 5th
day of incubation and becomes functional around the
10th to 12th day. It has an asymmetric sac-like shape and
a star-like lumen, which is continuous with the cloacal
cavity. The epithelium of the intestine covers the bursal
lumen but lacks mucous cells. The bursa contains abundant
lymphoid tissue, forming nodules beneath the epithelium.
The nodules show a central medullary region containing
epithelial cells and project into the epithelial coating. The
center of the medullary region is less structured and also
contains macrophages, large lymphocytes, plasma cells,
and granulocytes. A basement membrane separates the
medulla from the cortex; the latter is composed mostly
of small lymphocytes and plasma cells. The bursa is well
developed at birth but begins to involute around the fourth
month; it is vestigial at the end of the first year. There is
a direct relationship between the hormonal status of the
bird and involution of the bursa. Injections of testosterone
may lead to premature regression or even lack of development,
depending on the time of hormone administration.
The lymphocytes in the bursa originate from the yolk sac
and migrate there via the bloodstream. They are composed
of B cells that undergo maturation to immunocompetent
cells capable of antibody synthesis. Bursectomy at the 17th
day of incubation induces agammaglobulinemia, with the
absence of germinal centers and plasma cells in peripheral
lymphoid organs.
bursacyte
A lymphocyte that undergoes maturation and differentiation
under the influence of the bursa of Fabricius in avian
species. This cell synthesizes the antibody that provides
humoral immunity in this species. A bursacyte is a
B lymphocyte.
bursal equivalent
The anatomical site in mammals and other nonavian species
that resembles the bursa of Fabricius in controlling B
cell ontogeny. Mammals do not have a specialized lymphoid
organ for maturation of B lymphocytes. Although
lymphoid nodules are present along the gut, forming
distinct structures called Peyer’s patches, their role in B cell
maturation is no different from that of lymphoid structures
in other organs. After commitment to B cell lineage, the
B cells of mammals leave the bone marrow in a relatively
immature stage; likewise, after education in the thymus, T
cells migrate from the thymus, also in a relatively immature
stage. Both populations continue their maturation process
away from the site of origin and are subject to influences
originating in the environment in which they reside.
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Structure of busulfan.
bursectomy
The surgical removal or ablation of the bursa of Fabricius,
an outpouching of the hindgut near the cloaca in birds.
Surgical removal of the bursa prior to hatching or shortly
thereafter followed by treatment with testosterone in vivo
leads to failure of the B cell limb of the immune response
responsible for antibody production.
busulfan (1,4-butanediol dimethanesulfonate)
An alkylating drug that is toxic to bone marrow cells and is
used to condition bone marrow transplant recipients.
butterfly rash
A facial rash in the form of a butterfly across the bridge
of the nose seen especially in patients with lupus erythematosus.
These areas are photosensitive and consist of
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