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Summary and Explanation:
Human Immunodeficiency Virus Type (HIV-1) has been isolated from patients with AIDS and AIDS-related complex (ARC). HIV-1 was thought to be the sole causive agent of these syndromes until 1986, when a second type of Human Immunodeficiency Virus (HIV-2) was isolated and also reported to cause AIDS. Since the initial discovery, more than 600 cases of HIV-2 infection have been documented worldwide, with over 40 cases of AIDS related to HIV-2.
Both viruses have the same morphology and lymphotropism, and the modes of transmission appear to be identical. In addition, HIV-1 and HIV-2 genomes exhibit about 60% homology in conserved genes such as gag and pol. Serologic studies have also shown that the core proteins of HIV-1 and HIV-2 display frequent cross-reactivity whereas the envelope proteins are more type-specific.
Despite this immunologic cross-reactivity, detection of antibodies to HIV-2 with any of the licensed HIV-1 enzyme immunoassays is highly variable. This HIV-1/HIV-2 EIA was developed to detect antibodies to HIV-1 and /or HIV-2, for blood screening and diagnostic purposes.
Any specimen that reacts in an initial test with the HIV-1/HIV-2 EIA must be retested in duplicate with the Diagnostic Automation, Inc. Biotech Corporation's HIV-1/HIV-2 EIA. Repeatably reactive specimens may contain antibodies to either HIV-1 or HIV-2. Therefore, additional, more specific or supplemental tests for antibodies to both HIV-1 and HIV-2 such as immunoblot, immunofluorescence, radioimmuno-precipitation must be performed to verify presence of antibodies to HIV.
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Biological Principles of the Assay:
The DAI HIV-1/HIV-2 EIA utilizes a detection system where microplate wells are coated with synthetic peptides and recombinant antigen corresponding to a highly antigenic segment of HIV-1/HIV-2 envelope and core proteins. Serum or plasma specimens, controls are added to the wells. During incubation, antibodies specific for HIV-1 and HIV-2 present in the specimen will bind to the peptides and recombinant antigen fixed onto the microplate wells. The wells are washed to remove unbound materials, and recombinant antigen conjugated with horseradish peroxidase are added to the wells. The enzyme conjugate will bind to the antigen-antibody complex and excess unbound enzyme conjugates are again removed by washing. The enzyme substrate, tetramethylbenzidine (TMB), is added upon incubation the substrate will be hydrolyzed by the bound enzyme and a blue or blue-green colour develops in wells containing HIV-1 and/or HIV-2 specific antibodies. The enzyme reaction is stopped by the addition of sulphuric acid. The intensity of colour developed is read spectrophotometrically at 450nm and is proportional to the amount of antibodies present in the specimen.
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