HIV p24 antigen question...

[BlackNDecker]

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Why is the p24 protein the first detectable Ag in infected patients(Robbins p.246 ed.7), despite the fact that it is buried deep within the viral capsule? Why wouldn't gp120 or gp41 be detectable first?

Is the virus transmitted in its fully clothed form(i.e. gp120/gp41 associated lipid bilayer, p17 matrix, and p24 capsid)? If so, I would expect to see gp120/gp41 and p17 Ag first...

Also, what is the significance of the proviral genome? Is this the form of the virus that is transmitted during sex & IV drug usage? Is there a difference in expression of any of the cell surface Ag(i.e. gp120/gp41/p17)?

 

[pseudoknot]

p24 makes up the viral capsid. In a typical virion there are ~5000 copies of that molecule. The number of surface proteins (gp120/gp41) is hotly disputed but is likely to be in the dozens or low hundreds. It therefore would make sense that p24 could be more easily detected.

As for your second question, yes, the viral particles have all those proteins and the bilayer, until they fuse with the host cell.

The proviral genome is the DNA copy that is integrated into the host genome. I'm not clear on what you mean with your last question--a difference in expression between what two things?

p17, by the way, is not a surface protein; it's complexed with the RNA genome deep within the viral core.

 

[BlackNDecker]

p24 makes up the viral capsid. In a typical virion there are ~5000 copies of that molecule. The number of surface proteins (gp120/gp41) is hotly disputed but is likely to be in the dozens or low hundreds. It therefore would make sense that p24 could be more easily detected..

Thanks for the response. This makes sense on a #'s basis... Is p17 also expressed in low numbers, hence a virtually absent humoral response towards this Ag?

If the majority of the Ab is directed towards p24, then why does the ELISA test screen for gp120 Abs? (I got this ELISA info. from Goljan's Rapid Review...I haven't found any other sources that say what the ELISA & Western blot tests are sensitive/specific for)...any help on this matter would be appreciated.

p17, by the way, is not a surface protein; it's complexed with the RNA genome deep within the viral core.

I am aware that p17 is not a surface protein...the diagrams I've seen(Robbins mostly) show that it is expressed in the matrix between the capsid(which as I understand it contains the viral core) and the lipid bilayer.

 

[BlackNDecker]

A quick search answered the ELISA/Western blot question. For those interested:

ELISA:
http://www.biology.arizona.edu/immunology/activities/elisa/main.html

Western blot: http://www.biology.arizona.edu/immunology/activities/western_blot/west2.html

Miscellaneous:
http://health.yahoo.com/centers/hiv_aids/40004

 

[pseudoknot]

Thanks for the response. This makes sense on a #'s basis... Is p17 also expressed in low numbers, hence a virtually absent humoral response towards this Ag?

p17 (MA or matrix) and p24 (CA or capsid) are expressed as part of the Gag polyprotein, so their numbers should be equal in each virion. I do not know what accounts for the difference in immune response.

I am aware that p17 is not a surface protein...the diagrams I've seen(Robbins mostly) show that it is expressed in the matrix between the capsid(which as I understand it contains the viral core) and the lipid bilayer.

I shouldn't have been posting so late at night. The comment about being within the core referred to nucleocapsid (NC), not MA/p17. The MA or p17 protein is just below the lipid bilayer and is in fact bound to it. Your comment below implied that you did think it was a surface protein, hence my reply. Sorry for any confusion.

Is there a difference in expression of any of the cell surface Ag(i.e. gp120/gp41/p17)?