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Interferon Gamma Release Assays

Interferon Gamma Release Assays are a class of assays for viral and infectious diseases that measure the cell mediated response in infected individuals through the levels of interferon gamma released. During an infection, T cells from the individual will be senstized (via MHC proteins) to the antigens presented by cells of the infecting organism. T cells will thus be able to bind to foreign infecting cells, releasing interferon-gamma.

Interferon Gamma Release Assays take advantage of this natural process in infected immunocompetent individuals. When antigens specific for a given infecting agent (often in the form of purified protein derivatives) are applied to whole-blood samples from infected individuals, T cells sensitized to the antigens will be present in the blood, and will bind to the antigen. The T cells will then release Interferon-Gamma; the presence of sensitized T-cells in infected individuals will result in far higher levels of IFN-G release than among uninfected individuals.

The presence of IFN-G can then be quantified using a single step enzyme-linked immunosorbent assay (ELISA) using anti-IFN-G antibodies.

 

Image from Cellestis Website: http://www.cellestis.com/IRM/content/compinfo/pic_4_3pic1.gif
 


 

QuantiFERON®-TB
The original IGRA-type assay (originally approved for use by the FDA in 2001) developed for use for TB diagnosis. The test measures the release of IFN-G when heparinized whole blood samples are incubated with purified protein derivative from M. tuberculosis. The test is no longer available for use. [CDC]

QuantiFERON®-TB Gold
The only new diagnostic approved by the FDA (2004), the QFT-Gold assay is slowly being implemented in the United States.

QuantiFERON®-Gold In Tube Assay
The newest development in IGRAs, the In Tube assay is available for use in other countries but has yet to be approved by the FDA.