Brian T Foley,
Los Alamos National Lab, Los Alamos NM 87545
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I repeat "If the Perth Group would like to claim that density gradient
ultracentrfugation is the ONLY acceptable method of isolating a virus,
they should provide some evidence that any virus has ever been isolated
by that method to their satisfaction, preferably another retrovirus. "
The Perth group is using a simple "straw man" argument, in claiming that their method is the only acceptable method of analyzing a virus, when in fact their method has requirements included which make it IMPOSSIBLE to follow. It is well known that lentiviruses have mature and immature forms, with the electron dense core gradually forming as the viral particles mature. Thus any photograph of HIV or SIV or EIAV shows viral particles that are not all 100% identical.
Density gradient ultracentifugation is also rather harmful to viruses so that the viral particles loose much or all of their ability to infect cells after this treatment. In addition to osmotic stress from the solutes used to generate the density gradient, there is also physical stress of ultracentrifugation which tends to remove viral envelope glycoprotein spikes.
If the Perth group believes that their method is valid for studying viruses, they should be able to name at least one virus which has been studied using their criteria. Where is the evidence that ANY virus has EVER been "purified" to their satisfaction??????
Competing interests: None declared