Re: Re: Re: Some Random Comments 1 November 2004
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Peter J Flegg,
Physician
Blackpool, UK

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Re: Re: Re: Re: Some Random Comments

Being a clinician rather than a virologist, I am unable to answer some of Mark Bartlett’s questions, such as which antibody assays were not developed from reference isolates of the relevant virus. I believe that for HIV assays on plasma, different tests require different dilutions ranging from undiluted, neat plasma up to 400x dilutions.

Mark’s reference to “rising titres” with some other tests is a red herring – some pathogens are indeed diagnosed using this technique, when a demonstrable rise in IgG titre is found following acute infection, and the assay plate will run both specimens (early and convalescent) in parallel at a range of different dilutions to see if antibody may still be detectable at weaker dilutions in the convalescent sample (indicating a “rising titre”, or positive result). HIV assays do not work on this principle. All we really wish to know is whether antibody is present or not. However, in recently acquired HIV infection, it is possible to use a “detuned” assay, which detects lower antibody levels and differing antibody avidities that are typically found within the first few months. These assays can be used in epidemiological surveys to detect the extent of more recent HIV infection, giving useful estimates of HIV incidence rather than prevalence, but would never be used as a clinical diagnostic aid.

The FDA website gives a list of FDA-approved assays for the detection of HIV antibodies. Many of these do not require dilution steps, but use neat plasma/whole blood, dried blood spots, saliva/mouth swabs or urine. (Some of these, such as dried blood spots, need to have the blood “dissolved” out with an elution step).

Whether the immune system can return to a normal state if HIV were completely eradicated from the host is unclear. It seems that long term infection can result in significant changes in lymph node architecture. There are many individuals who have had successfully suppressed HIV to undetectable levels for several years who have not shown a full restoration of T cell responses. I suspect that with early-treated infection, the chances of full restoration are far greater, but it may be that some damage is irreversible.

References:

FDA site: http://www.fda.gov/cber/products/testkits.htm

HIV InSite (AIDS knowledge base) on HIV tests: http://hivinsite.ucsf.edu/InSite?page=kb-02-02-01#

Competing interests: None declared