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B cell mitogen 95 B lymphocyte
infectious mononucleosis or a proliferating and relentless
lymphoma that produces high mortality. Monoclonal antibodies
to the B cell antigens, CD21 and CD24, have proven
effective in controlling the B cell proliferation, but further
studies are needed.
B cell mitogen
Substance that induces B cell division and proliferation.
B cell receptor (BCR) complex
The antigen receptors of B cells, each of which makes a
single type of immunoglobulin. The form of this immunoglobulin
on the cell surface is the B cell receptor for
the antigen of interest in addition to the membranebound
immunoglobulin monomers of the intracellular
signaling molecules that comprise the accessory Igα/Igβ
complex.
B cell-specific activator protein (BSAP)
A transcription factor that has an essential role in early
and later stages of B cell development. It is encoded by the
gene Pax-5.
B cell-stimulating factor 1 (BSF-1)
An earlier term for interleukin-4.
B cell-stimulating factor 2 (BSF-2)
An earlier term for interleukin-6.
B cell tolerance
B cell tolerance is manifested as a decreased number of
antibody-secreting cells following antigenic stimulation,
compared to a normal response. Hapten-specific tolerance
can be induced by inoculation of deaggregated haptenated
γ-globulins (Ig). Induction of tolerance requires membrane
Ig cross-linking. Tolerance may have a duration of 2 months
in B cells of the bone marrow and 6 to 8 months in T cells.
Whereas prostaglandin E (PGE) enhances tolerance induction,
interleukin-1 (IL-1), lipopolysaccharide (LPS), and
8-bromoguanosine block tolerance instead of an immunogenic
signal. Tolerant mice carry a normal complement
of hapten-specific B cells. Tolerance is not attributable to
a diminished number or isotype of antigen receptors. It
has also been shown that the six normal activation events
related to membrane Ig turnover and expression do not
occur in tolerant B cells. Although tolerant B cells possess a
limited capacity to proliferate, they fail to do so in response
to antigen. Antigenic challenge of tolerant B cells induces
them to enlarge and increase expression, yet they are apparently
deficient in a physiologic signal requisite for progression
into a proliferative stage.
B cell tyrosine kinase (Btk)
Src family tyrosine kinase that plays a critical role in the
maturation of B lymphocytes. Btk gene mutations lead to
X-linked agammaglobulinemia in which B cell maturation
is halted at the pre-B stage.
B cells
The B lymphocytes that derive from the fetal liver in the
early embryonal stages of development and from the bone
marrow thereafter. In birds, maturation takes place in the
bursa of Fabricius, a lymphoid structure derived from an
outpouching of the hindgut near the cloaca. In mammals,
maturation is in the bone marrow. Plasma cells that synthesize
antibody develop from precursor B cells.
B complex
The major histocompatibility complex (MHC) in chickens.
Genes at these loci determine MHC class I and II antigens
and erythrocyte antigens.
9–12µm
B cell.
B genes
Situated within the major histocompatibility complex
(MHC) locus on the short arm of chromosome 6, they are
called MHC class III genes. TNF-α and TNF-β genes are
situated between the C2 and HLA-B genes. Another gene
designated FD lies between the Bf and C4a genes. C2 and
B complete primary structures have been deduced from
cDNA and protein sequences. C2 is comprised of 732
residues and is an 81-kDa molecule, whereas B contains 739
residues and is a 83-kDa molecule. Both proteins have three
domains. Certain HLA alleles occur at a higher frequency
in individuals with particular diseases than in the general
population. This type of data permits estimation of the relative
risk (RR) of developing a disease for every known HLA
allele. For example, there is a strong association between
ankylosing spondylitis, an autoimmune disorder involving
the vertebral joints, and the major histocompatibility
complex (MHC) class I allele, HLA-B27. There is a strong
association between products of the polymorphic class II
alleles HLA-DR and DQ and certain autoimmune diseases,
as MHC class II molecules are of great importance
in the selection and activation of CD4 + T lymphocytes that
regulate immune responses against protein antigens. For
example, 95% of Caucasians with insulin-dependent (type
I) diabetes mellitus have HLA-DR3, HLA-DR4, or both.
There is also a strong association of HLA-DR4 with rheumatoid
arthritis. Numerous other examples exist and are
the targets of current investigations, especially in extended
studies employing DNA probes. Methods of calculating the
RR and absolute risk (AR) can be found under definitions
for those terms.
B locus
The major histocompatibility locus in the chicken.
B lymphocyte
Lymphocytes of the B cell lineage that mature under the
influence of the bursa of Fabricius in birds and in the bursa
equivalent (bone marrow) in mammals. B cells occupy follicular
areas in lymphoid tissues and account for 5 to 25% of
all human blood lymphocytes that number 1000 to 2000 cells
per mm 3 . They comprise most of the bone marrow lymphocytes,
one third to one half of the lymph node and spleen
lymphocytes sites, but less than 1% of those in the thymus.
Nonactivated B cells circulate through the lymph nodes and
the spleen. They are concentrated in follicles and marginal
zones around the follicles. Circulating B cells may interact
B