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double diffusion test 235 double-stranded DNA autoantibodies
Lines of
precipitation
Double diffusion test.
Soluble
antigen
Neutral zone
(plain agar)
Antibody
in agar
double diffusion test
A test in which soluble antigen and antibody are placed in
separate wells of a gel containing electrolyte. The antigen
and antibody diffuse toward one another until their
molecules meet at the point of equivalence and precipitate,
forming a line of precipitation in the gel. In addition to the
two-dimensional technique, double immunodiffusion may
be accomplished in a tube as a one-dimensional technique.
The Oakley–Fulthorpe test is an example of this type of
reaction. This technique may be employed to detect whether
antigens are similar or different or share epitopes. It may
also be used to investigate antigen and antibody purity.
Refer also to reaction of identity, reaction of nonidentity,
and reaction of partial identity.
double emulsion adjuvant
Water-in-oil-in-water emulsion adjuvant.
double immunodiffusion
A precipitation reaction in gel media in which both antibody
and antigen diffuse radially from wells toward each
other, thereby forming a concentration gradient. A visible
line of precipitation forms as equivalence is reached.
double layer fluorescent antibody technique
An immunofluorescence method to identify antigen in a
tissue section or cell preparation on a slide by first covering
and incubating it with antibody or serum containing
antibody that is not labeled with a fluorochrome. After an
appropriate time for interaction, the preparation is washed,
and a second application of fluorochrome-labeled antibody
such as goat or rabbit antihuman immunoglobulin is applied
to the tissue or cell preparation and it is again incubated.
This technique has greater sensitivity than does the single
layer immunofluorescent method. Examples include applying
serum from a patient with Goodpasture’s syndrome to a
normal kidney section that acts as substrate, incubating and
washing, and then covering the preparation with fluorochrome-labeled
goat antihuman immunoglobulin G (IgG) to
detect antiglomerular basement membrane antibodies in the
patient’s serum. A similar procedure is used in detecting
antibodies against intercellular substance antigens in the
serum of patients with pemphigus vulgaris.
double negative (DN) cell
A stage in the development of T lymphocytes in which differentiating
α/β T lymphocytes do not possess T cell receptors
and do not manifest either the CD4 or the CD8 coreceptor.
double negative thymocyte
Immature T cell that fails to express either CD4 or CD8
molecules. CD4 – CD8 – thymocytes that are few in number
and serve as progenitors for all other thymocytes. They
represent an intermediate step between pluripotent bone
marrow stem cells and immature cells destined to follow T
cell development. Significant heterogeneity is present in this
cell population. Peripheral extrathymic CD4 – CD8 – T cells
have been examined in both skin and spleens of mice, and,
like their corresponding cells in the thymus, they express T
cell receptor (TCR) γδ proteins. These double negative cell
populations are greatly expanded in certain autoimmune
mouse strains such as those expressing the lpr or gld genes.
Available evidence reveals two thymic populations of CD4 –
CD8 – cells. Immature double negative bone marrow graft
cells have stem cell features. However, double negative cells
of greater maturity and without stem cell functions quickly
repopulate the thymus. Most double negative thymocytes
are in an early stage of development and fail to express
antigen receptors.
double positive (DP) cell
A T lymphocyte developmental stage in which differentiating
α/β T cells manifest the pre-T cell receptor and both
CD4 and CD8 coreceptors.
double positive thymocyte
Cell at an intermediate stage of T lymphocyte development
in the thymus that expresses both the CD4 and CD8
coreceptor proteins. These thymocytes also express T cell
receptors and are exposed to selection processes that culminate
in mature single-positive T lymphocytes that express
only CD4 or CD8.
double-stranded DNA antibodies
Antibodies associated with systemic lupus erythematosus
(SLE) that may be studied serially using the Farr (ammonium
sulfate precipitation) assay to predict activity of the
disease and monitor treatment. dsDNA antibody levels are
interpreted in conjunction with serum C3 or C4 concentrations.
If the dsDNA antibody level doubles or exceeds 30
IU/mL earlier than 10 weeks, an exacerbation of SLE is
likely, especially if there is an associated decrease in the
serum C4 concentration. This reflects selective stimulation
of B cell stimulation known to occur in SLE patients. The
Farr assay is more reliable than the enzyme immunoassay
method, because the Farr assay measures high avidity
antibodies to dsDNA.
double-stranded DNA autoantibodies
Increased concentrations of high affinity, anti-dsDNA
(double-stranded DNA) autoantibodies detected by the Farr
method to serve as a reliable predictor of systemic lupus
erythematosus (SLE). When detected, these antibodies can
foretell the development of SLE within a year in approximately
two thirds of patients without clinical evidence of
SLE. Currently used tests often measure dsDNA autoantibodies
of varying affinities that give positive and confusing
results in non-SLE patients. Autoantibodies against ssDNA
have no clinical significance except as a general screen for
autoantibodies. Patients with exacerbations of SLE develop
higher concentrations of dsDNA autoantibodies. Doubling
of autoantibody levels within 10 weeks, an increase of
30 IU/mL, or an increase of 25% from the lowest value during
the preceding 4 months can predict disease exacerbations
90% of the time. In SLE patients with central nervous
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