Posts Tagged ‘insects’

TMV in mouse lungs: more thoughts and refutations

13 February, 2013

tmv sedimhave been thinking about this paper (see last post), and it and other people’s posts (eg: Tommy Leung’s) have prompted more response.

I note the authors  say the following:

“There is other published literature that challenges the dogma of the strict boundaries between plants and vertebrates for viruses. In non-vertebrate animals, it was shown that plant pathogenic viruses displayed complex interactions with insects, and the transcription and replication of some plant viruses within insects was described [29][32]. In addition, in some cases, insects were found to be affected by plant viruses [33]. Furthermore, it was recently shown that Tomato spotted wilt virus (TSWV) could infect two human cell lines, HeLa and diploid fibroblasts, depending on the expression of a viral polymerase-bound host factor[34]. Additionally, despite plant virus replication was not observed in animals, Cowpea mosaic virus (CPMV), a plant comovirus in the picornavirus superfamily, was able to bind and enter mammalian cells, including endothelial cells, and the binding protein for the virus was identified as a cell-surface form of the intermediate filament vimentin [35]. Furthermore, CPMV was found to persist for several days post oral or intravenous inoculation in a wide panel of body tissues in mice, including in the lung and the liver [36]. Additionally, it was demonstrated that TSWV induced a strong immune response in its insect vector Frankliniella occidentalis [37] and that oral administration of Cowpea severe mosaic virus, Alfalfa mosaic virus and chimeric plant virus particles induced a durable and systemic immune response in mice [38][39]

Yes.  Um. Well.  The “dogma of the strict boundaries between plants and vertebrates for viruses”?  I have been teaching virology for 32 years, and I am not aware of actual DOGMA – as in, “that which has to be believed”.  Rather, there has been the cumulative set of OBSERVATIONS that nothing that anyone has ever isolated out of a plant – and that replicates in it – has infected a vertebrate.  I make that distinction, because there is always the possibility that, as we and others have found with insect viruses, plants can act as a “circulative, non-propagative vector” for insect viruses (for Rhopalosiphum padi aphid virus in barley, from my lab, and Leafhopper A virus in maize) – and if one realises that male mosquitoes, and often also females, feed on plants…you see where I’m going here?  As in, it might well be possible for a virus that multiplies in an insect and also in a vertebrate, to POTENTIALLY be found in a  plant?

In ay case, this is largely beside the point, because the authors get sidetracked into discussing Tomato spotted wilt – which happens to be a plant-adapted bunyavirus, most closely related to insect and vertebrate phleboviruses – “depending on the expression of a viral polymerase-bound host factor”.  Really??  And if it isn’t there?  Does the virus in fact spread?  For that matter, my lab has cell-free translated two aphid picorna-like virus genomes in rabbit reticulocyte lysates, but we made no claim that it could happen in rabbit cells.  Moreover, they make much of the fact that “a plant comovirus in the picornavirus superfamily, was able to bind and enter mammalian cells…[and] was found to persist for several days post oral or intravenous inoculation in a wide panel of body tissues in mice, including in the lung and the liver”.

Yes?  And?  A REALLY stable plant virus was able to bind and enter animal cells, and persist?  The problem with that is…?

We in the virus-like particle vaccine field RELY on the fact that VLPs will be taken up by cells of the immune system in vertebrates, and that they will elicit immune responses – so why is this regarded as a problem?  In fact, TMV has itself been tested as an RNA vaccine delivery system, due to its ability to protect a RNA payload, and get itself delivered into reticulocytes and macrophages – meaning this property has been known for some time, and has not hitherto been seen as a problem!

I think these authors have hyped something that is quite interesting into what THEY regard as a potential problem, for the purposes of getting their article accepted – and I think this needs to be recognised, and that the perceived risks need to be minimised by the knowledgeable.

PLOS ONE: Tobacco Mosaic Virus in the Lungs of Mice following Intra-Tracheal Inoculation

13 February, 2013

See on Scoop.itVirology News

“Plant viruses are generally considered incapable of infecting vertebrates. Accordingly, they are not considered harmful for humans. However, a few studies questioned the certainty of this paradigm. Tobacco mosaic virus (TMV) RNA has been detected in human samples and TMV RNA translation has been described in animal cells. We sought to determine if TMV is detectable, persists, and remains viable in the lung tissues of mice following intratracheal inoculation, and we attempted to inoculate mouse macrophages with TMV. In the animal model, mice were intratracheally inoculated with 1011 viral particles and were sacrificed at different time points. The virus was detected in the mouse lungs using immunohistochemistry, electron microscopy, real-time RT-PCR and sequencing, and its viability was studied with an infectivity assay on plants. In the cellular model, the culture medium of murine bone marrow derived macrophages (BMDM) was inoculated with different concentrations of TMV, and the virus was detected with real-time RT-PCR and immunofluorescence. In addition, anti-TMV antibodies were detected in mouse sera with ELISA. We showed that infectious TMV could enter and persist in mouse lungs via the intratracheal route. Over 14 days, the TMV RNA level decreased by 5 log10 copies/ml in the mouse lungs and by 3.5 log10 in macrophages recovered from bronchoalveolar lavage. TMV was localized to lung tissue, and its infectivity was observed on plants until 3 days after inoculation. In addition, anti-TMV antibody seroconversions were observed in the sera from mice 7 days after inoculation. In the cellular model, we observed that TMV persisted over 15 days after inoculation and it was visualized in the cytoplasm of the BMDM. This work shows that a plant virus, Tobacco mosaic virus, could persist and enter in cells in mammals, which raises questions about the potential interactions between TMV and human hosts.”

Ed Rybicki‘s insight:

Interesting paper!  Which proves…which proves…which proves TMV is seriously resistant to degradation in animals and in mammalian cells; that it can enter macrophages; and that it…what?  What, exactly, are the “…questions about the possible interactions…”?  What would TMV do in mammalian cells?  Yes, it might be uncoated and be translated; it is far less likely that it MIGHT be able to replicate its RNA – and then?  While it can apparently be taken up quite efficiently by macrophages – a property which, incidentally, has led to its being trialled as an RNA vaccine delivery system – this is a dead end, and one that is quite normal for particles of any kind being introduced into mammals.

Which is something that happens every day, as we and our cousin mammals eat: it has been shown elsewhere that animals are actually quite good spreaders of plant viruses, some of which – like TMV and the even tougher Cauliflower mosaic virus – pass right through at high survival rates, and remain infectious.  We will all probably have eaten many grams of various viruses in our lives, and derived nothing more than nutrition from them.

I also remember, even though it was very late at night, 31 years ago, and in a bar in Banff in Canada, a conversation with one Richard Zeyen.  He told me they had used ELISA to test everyone in their lab for antibodies for TMV, seeing as they worked with it, and had newly developed a test.  And everyone was immune – presumably, to aerosolised TMV that had been breathed in or otherwise ingested.  Proving…that oral vaccines based on TMV could work, and that most of us are probably immune to all sorts of viruses that don’t replicate in us – and nothing more!

Including, in the case of many people in the Eastern Cape Province of South Africa, sampled by one Don Hendry via the local blood bank, to a virus of Pine Emperor moths – because it multiples to such high levels in its host that anyone walking in the pine forests was bound to be exposed via the environment.

So this is an interesting paper – and no more.  It will, of course, lead to alarmist articles and blog posts, and people calling out for urgent surveillance of food, in which people will find many viruses.  And so what?  They have been with us for as long as we have been eating plant-derived food, and have NEVER been associated with any disease, transmissible or otherwise – so my best advice is that we ignore them.

See on www.plosone.org


Follow

Get every new post delivered to your Inbox.

Join 533 other followers