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USMLE Western blot for HIV - Looking for antibodies? (FA 2014)

Discussion in 'Step I' started by Freddie Mercury, May 19, 2014.

  1. Freddie Mercury

    Freddie Mercury Bismillah! No, we will not let you go! 5+ Year Member

    Apr 27, 2012
    Bohemian Rhapsody
    Question about HIV screening. First aid says "ELISA/Western blot tests look for antibodies to viral proteins".

    I understand the screening test is ELISA, where you would look for antibodies against HIV. But from various practice questions and Google research I've done, in Western Blot I don't think you'd be looking for antibodies, but rather the viral proteins themselves (p24, GP120 etc).
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  3. dyspareunia


    Mar 6, 2014
    In WB for HIV you pour the patient's serum onto a prepared sample containing HIV proteins. You are testing to see if the patient has antibodies to what you know are HIV proteins.

    The only difference between ELISA and WB is that in WB the proteins are electrophoresed first so you know which specific protein(s) the patient has antibody to. Hence, WB is more specific than ELISA.
  4. Enzymes

    Enzymes 2+ Year Member

    Mar 13, 2012
    I think I see what you are saying. In western blot, you are dealing with the HIV proteins first. You separate them out via gel electrophoresis. But then to actually visualize the proteins, you use antibodies (after blotting to a membrane). The same thing applies to ELISA, where the viral antigens are coating the plate, and you use visualize the antibodies that actually bind to the antigens. So ultimately, you are visualizing antibodies that are binding to the viral antigens. (both are present).

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