Saturday, August 13, 2011

Laboratory diagnosis of viral infections: Antigen detection

nullAntigen detection:
Immunological methods are highly effective for detection of viral antigens (Ag). They offer high degree of sensitivity and specificity, are rapid, and the costs are reasonable. Virtually all methods use antibodies that are tagged with a fluorochrome, enzyme, or radiolabel (Schutzbank and McGuire, 2000).
A) Immunofluorescence (IF):
The direct staining of clinical specimens using monoclonal or polyclonal antibodies (Abs) bound to fluorescent dye. This may be direct or indirect techniques. In direct IF, a single fluorochrome-labeled Ab is used. Indirect IF uses two Abs, one specific for the Ag and a second fluorochrome-labeled Ab to the immunoglobulin (Madeley and Peiris, 2002).
B) Enzyme Immunoassay (EIA):
Enzyme Immunoassay can perform to detect antigens in clinical specimens. This versatility has resulted in wide spread use of EIA in diagnostic virology. Most commonly these assays are performed using a solid phase format, as ELISA, with the particular target reagent bound to plastics in a microtiter well. EIA are generally high specific and sensitive, and rapid, within minutes to hours (Leland, 2000).
C) Radioimmunoassays (RIA):
Radioimmunoassays have fallen out of use for most viral assays due to exposure to radioisotope and the high cost of disposal of radioactivity. RIA rivals EIA in specificity and sensitivity (Mushahwar and Brawner, 2000).

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