Brian T Foley,
Los Alamos National Lab, Los Alamos NM 87545
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Bruno Spagnoli wrote:
I'd like to ask a question to Dr Nicholas Bennett, regarding the ELISA test and the experiments of Dr Giraldo.
Dr Bennett does not seem to challenge Dr Giraldo's findings, so I will assume he agrees that undiluted serum from any person would test positive on the ELISA.
reaction occurs, it means that in the blood of every person, there
exists a substance or set of substances, which, either separately or
together, cause a reaction with the antigens from the test, although
this reaction is confined to a low level. These substances can be
anything except HIV antibodies (it would be inconsistent with the
assumption that "negative" blood is non-infected). Let's call this set
of substances, "agent A".
The “substance” is human antibodies that bind to HIV-1 antigens which are present in the test. Any basic immunology textbook explains that vertebrates do not make new antibodies de novo when challenged with an antigen, they only increase the production of currently existing antibodies. Over time, challenged vertebrates also fine-tune the reactive antibodies to produce slightly modified antibodies with even higher affinities to the antigens, but that is another matter.
This is why it is not the absolute “yes” or “no” do antibodies exist in the blood that is used in ANY serological test, but the TITRE or level of those antibodies, that is important to measure. In addition, in many serological tests, it is equally important to observe the trend in titer over time. An increasing titre indicates an active or recent infection, while a high but decreasing titre can indicate that the infection has been cleared.
Bruno Spagnoli wrote:
My question is the following one : how can Dr Bennett (or anyone else) be absolutely certain that in the presence of a strong reaction, the reaction is *ALWAYS* caused by HIV antibodies and not by "agent A" present in higher concentration than usual ? (WB "confirmation" would not convince me more, since the antigens in both tests are the same)
Could Dr Bennett provide clear-cut experimental data which would rule out such a possibility ?
”Agent A” IS human antibodies reactive to HIV-1 antigens present in the ELISA test kit. Enzyme-Linked Immunosorbant Assays (ELISAs) usually use goat anti-human antibodies to detect human antibodies that are bound to the antigen, which is bound to the ELISA plate. The goat antibody is in turn linked to an enzyme that causes a color change. When the antigen is bound to the plate as in the HIV-1 ELISA, the ELISA is called an “antibody capture ELISA”.
If you don’t understand how ELISAs and other serological tests work, it is easy to become confused by the AIDS denialist propaganda. The antigens in a western blot are almost always different from those used in any given ELISA test. Yes, both use antigens from the same general class of viruses (typically HIV-1 M group and sometimes HIV-1 M group plus HIV-1 O group) but most often different antigens from those viruses. For example, and ELISA may contain synthetic peptides identical to peptides found in the envelope proteins (gp120 and/or gp41) of several different isolates from different subtypes of the HIV-1 M group. The Western Blot contains whole proteins, rather than peptides, and always contains many HIV-1 M group proteins such as Gag p17, Gag p24, Gag p7, Protease p15, Pol-RT p66, Pol-RT p51 as well as Env gp120 and Env gp41.
In an ELISA, any human antibodies that binds to any of the antigens bound to the plate gives a positive result if there are enough of them (if the specific antibody tire is high enough). Thus, a very high titre of antibody that is weakly cross-reactive with the antigen on the plate may give a false positive result. In a western blot, the exact size of the protein to which the antibodies are binding, is determined. Thus, and antibody that binds strongly to HTLV-II Gag protein might bind weakly to HIV-1 Gag protein, but the envelope proteins of these viruses are so dissimilar that no cross-reaction would occur. If this is true, then a person infected with HTLV-II might have a false positive ELISA but only one or a couple of the Gag bands would react on a western blot, and not any of the Env or other bands.
Although the AIDS denialists like to claim that only the number of reactive bands on a western blot has any meaning, in reality the exact pattern of the bands, and the change in reactivity of various bands over time, can be very useful in determining true HIV infections versus false positive ELISA and/or indeterminate western blot reactions. Sadly, many doctors know less about the interpretation of western blots than the medical technologists who routinely perform them.
Competing interests: None declared