A direct fluorescent antibody (DFA or dFA), also known as "direct immunofluorescence",
is an antibody that has been tagged in a direct fluorescent antibody test. Its name derives from the fact that it directly tests the presence of an
antigen
In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...
with the
tagged antibody, unlike
western blotting
The western blot (sometimes called the protein immunoblot), or western blotting, is a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detecti ...
, which uses an
indirect method of detection, where the primary antibody binds the target antigen, with a secondary antibody directed against the primary, and a tag attached to the secondary antibody.
Commercial DFA testing kits are available, which contain
fluorescently labelled antibodies, designed to specifically target unique antigens present in the bacteria or virus, but not present in mammals (
Eukaryotes
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
). This technique can be used to quickly determine if a subject has a specific viral or bacterial infection.
In the case of respiratory viruses, many of which have similar broad symptoms, detection can be carried out using nasal wash samples from the subject with the suspected infection. Although shedding cells in the respiratory tract can be obtained, it is often in low numbers, and so an alternative method can be adopted where compatible cell culture can be exposed to infected nasal wash samples, so if the virus is present it can be grown up to a larger quantity, which can then give a clearer positive or negative reading.
As with all types of
fluorescence microscopy
A fluorescence microscope is an optical microscope that uses fluorescence instead of, or in addition to, scattering, reflection, and attenuation or absorption, to study the properties of organic or inorganic substances. "Fluorescence microsc ...
, the correct
absorption wavelength needs to be determined in order to excite the
fluorophore
A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with se ...
tag attached to the antibody, and detect the fluorescence given off, which indicates which cells are positive for the presence of the virus or bacteria being detected.
Direct immunofluorescence can be used to detect deposits of
immunoglobulins
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
and
complement
A complement is something that completes something else.
Complement may refer specifically to:
The arts
* Complement (music), an interval that, when added to another, spans an octave
** Aggregate complementation, the separation of pitch-class ...
proteins in biopsies of skin, kidney and other organs. Their presence is indicative of an
autoimmune disease
An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...
. When skin not exposed to the sun is tested, a positive direct IF (the so-called
Lupus band test
Lupus band test is done upon skin biopsy, with direct immunofluorescence staining, in which, if positive, IgG and complement depositions are found at the dermoepidermal junction.Marks, James G; Miller, Jeffery (2006). ''Lookingbill and Marks' Pr ...
) is an evidence of
systemic lupus erythematosus
Lupus, technically known as systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Comm ...
.
[Ther Clin Risk Manag. 2011; 7: 27–32. The lupus band test in systemic lupus erythematosus patients. Adam Reich, Katarzyna Marcinow, and Rafal Bialynicki-Birula] Direct fluorescent antibody can also be used to detect parasitic infections, as was pioneered by
Sadun, et al. (1960).
See also
*
Immunofluorescence
Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on microbiological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specif ...
References
External links
*
{{DEFAULTSORT:Direct Fluorescent Antibody
Laboratory techniques
Clinical pathology
Immunologic tests
Reagents for biochemistry