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Types of antibody testing

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

HIV immunoassay technology

IV immunoassays based on different design principles are generally grouped into "generations":

  • 1st generation & 2 generation (indirect) enzyme linked immuno sorbent assay (ELISA)/enzyme immunoassays (EIAs)
    • plasma or serum is added to antigen coated wells containing viral lysate (first-generation assays) or recombinant HIV proteins or synthetic peptides (second-generation assays)
      • if anti HIV IgG is present in the sample it will bind to the antigens. An enzyme linked to anti-human IgG antibody is then added to the well (which binds to the anti-HIV IG). Finally a colour reagent is added.
        • a change in colour indicates the presence of anti-HIV IgG in the sample

  • 3rd generation "sandwich " ELISA
    • antigen coated well contains recombinant proteins or synthetic peptides. If the sample contains anti HIV IgG and IgM antibodies, it will bind with the antigen
      • an enzyme linked to HIV antigen is introduced (rather than to anti-IgG antibody) to the well which binds to anti HIV IgG and IgM
      • a colour reagent is added and if there is a change in colour it indicates the presence of anti-HIV IgG and IgM in the sample
    • useful in early detection of antibody response when compared to 1st and 2nd generation tests since they detect IgM as well as IgG

  • 4th generation "combination " ELISA
    • wells are coated with HIV antigen and p24 antibody
      • HIV antibodies in the sample binds to the antigen while anti p24 antibodies bind to the free p24
      • in the enzyme detection step, both enzyme-linked HIV antigen and enzyme-linked p24 antibody is added
      • a color change after addition of the color reagent indicates the presence of either anti-HIV antibody or p24 antigen
        • 2 different fluorescent labels can be used for independent detection of p24 antibody or HIV antigen.
    • when compared to previously available assays, 4th generation EIAs detect p24 antigens which enables even earlier detection of HIV infection (1)

Reference:

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