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asophil 102 Bcl-2 family
A peripheral blood basophil showing a bilobed nucleus and cytoplasmic
granules that represent storage sites of pharmacological mediators of
immediate type I hypersensitivity.
Neutrophil and basophil in peripheral blood.
basophil
A polymorphonuclear leukocyte of myeloid lineage with
distinctive basophilic secondary granules in the cytoplasm
that frequently overlie the nucleus. These granules are
storage depots for heparin, histamine, platelet-activating
factor, and other pharmacological mediators of immediate
hypersensitivity. Degranulation of the cells with release
of these pharmacological mediators takes place following
crosslinking by allergens or antigens of Fab regions
of IgE receptor molecules bound through Fc receptors to
cell surfaces. They comprise less than 0.5% of peripheral
blood leukocytes. Following crosslinking of surface-bound
IgE molecules by specific allergen or antigen, granules
are released by exocytosis. Substances liberated from the
granules are pharmacological mediators of immediate (type
I) anaphylactic hypersensitivity.
basophil-derived kallikrein (BK-A)
BK-A represents the only known instance in which an activator
of the kinin system is generated directly from a primary
immune reaction. The molecule is a high molecular
weight enzyme with arginine esterase activity. It is stored in
the producing cells in a preformed state. Its release depends
on basophil–IgE interactions with antigen and parallels the
release of histamine.
basophilic
An affinity of cells or tissues for basic stains leading to a
bluish tint.
BCDF
Abbreviation for B cell differentiation factor.
BCG (bacille Calmette–Guérin)
A Mycobacterium bovis strain maintained for more than
75 years on potato, bile, glycerine agar that preserves
the immunogenicity but dissipates the virulence of the
microorganism. It has long been used in Europe as a
vaccine against tuberculosis, although it never gained
popularity in the United States. It has also been used in
tumor immunotherapy to nonspecifically activate immune
responses in selected tumor-bearing patients, such as those
with melanoma or bladder cancer. It has been suggested as
a possible vector for genes that determine human immunodeficiency
virus (HIV) proteins such as gag, pol, env,
gp20, gp40, reverse transcriptase, and tetanus toxin. In
certain countries with high incidences of tuberculosis,
BCG provides effective immunity against the disease,
diminishing the risk of infection by approximately 75%.
The vaccine has the disadvantage of rendering skin testing
for tuberculosis inaccurate, especially in the first 5 years
after inoculation, because it induces hypersensitivity to
tuberculin. Intended for protection against tuberculosis in
individuals not previously infected with Mycobacterium
tuberculosis who are at high risk for exposure. Designed
for percutaneous use as an attenuated live culture preparation
of the Bacillus of Calmette and Guerin (BCG)
strain of M. bovis. The TICE strain was developed at
the University of Illinois from a strain originated at the
Institut Pasteur in Paris.
BCGF (B cell growth factor)
See interleukins 4, 5, and 6.
BCG vaccine
Refer to BCG (bacille Calmette-Guérin).
Bcl-2
A 25-kDa human oncoprotein that is believed to play a
regulatory role in tissue development and maintenance in
higher organisms by preventing the apoptosis of specific
cell types. The inhibitory effect of Bcl-2 is influenced by
the expression of other gene products such as bax, bcl-xs,
bak, and bad that promote apoptosis. Bcl-2 is situated at the
outer membranes of mitochondria, the endoplasmic reticulum,
and the nuclear membrane and may prevent apoptosis
either by acting at these locations or as an antioxidant
that neutralizes the effects of reactive oxygen species that
promote apoptosis or by obstructing mitochondrial channel
openings, thereby preventing the release of factors that promote
apoptosis. Bcl-2 is involved in the development of the
adult immune system as demonstrated by studies with Bcl-2
knockout mice. Failure to induce normal levels of apoptosis
due to overexpression of Bcl-2 may contribute to the development
of lymphoproliferative disorders and acceleration
of autoimmunity under the appropriate genetic background.
The role of Bcl-2 in human systemic lupus erythematosus
(SLE) and PSS has not yet been fully defined.
Bcl-2 family
The Bcl-2 family consists of proteins that share homology
to Bcl-2 in one or more of the Bcl-2 homology regions
designated BH1, BH2, BH3, and BH4. Many of the family
members have carboxyl-terminal mitochondrial membrane
targeting sequences. All have two central membrane-spanning
helices surrounded by additional amphipathic helices.
X-ray crystallographic studies have shown that Bcl-x L
has structural similarity to diphtheria toxin and colicins.
Diphtheria toxin is endocytosed by cells. Acidification of