Immunology question HIV ELISA vs. Western Blot

[Doc Ivy]

Does anyone know when they do a Western Blot for HIV are they testing for gp 24, 120, 17, 41 antibody etc, or is the western blot against the viral proteins themselves?

I understand why a newborn would have a positive ELISA but I'm confused how a baby can be born with a positive Western blot and not be infected.

Thanks

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[Wrigleyville]

My understanding is that both ELISA and western blot are looking for antibodies against viral proteins. Looking at the appropriate bands on a western blot, two out of three of: p24, gp41, gp120/160 is a positive, one is indeterminate, zero is negative.


The infant should be positive for both, but negative on PCR if not infected.

 

[Doc Ivy]

Thanks a bunch

 

[HiddenTruth]

Wrigleyville is right. ELISA is positive because the infant has mother's antibodies (that's all you know). While, WB will also be postitive, but these are mom's antibodies against SPECIFIC HIV ag's. So, only test to make sure that baby does not have HIV is to check for cDNA (which has been injected into cell) with PCR.

 

[omarsaleh66]

Goljan says that ELISA works via targeting gp120. I always thought ELISA did it for p24. Can anyone make sense of this?

Thanks

 

[HiddenTruth]

Goljan says that ELISA works via targeting gp120. I always thought ELISA did it for p24. Can anyone make sense of this?

Thanks

I think ELISA will detect any maternal antibodies that the child may have against HIV ag's. I don't think it's specific; THe WB is specific however. But, I despise this stuff, so someone else may want to actually explain this a little better.

 

[apara]

ELISA can detect- antibodies,antigens,haptens
western blot is for proteins only..........

 

[alhkim]

typically, the ELISA is against the p24 antigen, and at least a few years ago, it was against the antigen itself, not the antibodies. Since it has a relatively high false positive rate, the Western blot to check for p24 antigen is then performed.

There may be new ELISA/WB protocols to check for other antigens or antibodies against these antigens now though.

Goljan says that ELISA works via targeting gp120. I always thought ELISA did it for p24. Can anyone make sense of this?

Thanks

 

[alhkim]

the ELISA can also detect proteins (as you say antigens) as long as you have the capture and detection antibodies against that protein/antigen. As for WB, you only need one antibody against the protein/antigen/antibody as long as it works on the nitrocellulose paper that the proteins are bound on.

ELISA can detect- antibodies,antigens,haptens
western blot is for proteins only..........

 

[Doc Ivy]

the ELISA can also detect proteins (as you say antigens) as long as you have the capture and detection antibodies against that protein/antigen. As for WB, you only need one antibody against the protein/antigen/antibody as long as it works on the nitrocellulose paper that the proteins are bound on.

Yeah, this rings a bell. ELISA can be used for antigens if you use the "sandwhich" technique-- I think. But it's a little more complicated because you have to raise antibodies against the antigen in question-- so I think for HIV screening they just do the regular/cheaper ELISA for antibody.

 

[ucbdancn00]

Does anyone know when they do a Western Blot for HIV are they testing for gp 24, 120, 17, 41 antibody etc, or is the western blot against the viral proteins themselves?

I understand why a newborn would have a positive ELISA but I'm confused how a baby can be born with a positive Western blot and not be infected.

Thanks

to actually say someone is infected you need 2 out of 3 positive ab bands on western blot (confirmatory) following a positive ELISA; gp120, gp41, p24 (core protein). Gp120/gp41 are structural proteins.

if a baby is positive for an "infection" via ElISA and Western, you're only being told that the mom's IgG ab have made their way across the placenta and into the child. This would tell you that the mom is infected. This doesn't tell you that there is a circulating viral load in the baby; you would probably need to do a PCR test on the child and also look for an increased IgM as sign of in utero infection.

hope this helps.

ucb

 

[alhkim]

the sandwich technique is more complicated because you have to raise TWO antibodies, not just one, to the antigen (one that is on the plate that will attach to the antigen, and another antibody that will bind the antigen at another site away from the first antibody).

Yeah, this rings a bell. ELISA can be used for antigens if you use the "sandwhich" technique-- I think. But it's a little more complicated because you have to raise antibodies against the antigen in question-- so I think for HIV screening they just do the regular/cheaper ELISA for antibody.