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There are typically hundreds of retroviruses found in healthy human beings.

Are retroviruses then cytotoxic? (In other words, are they able to kill or damage other cells).

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Can you please expand your question? Actually I am not sure what you are asking. –  Chris Sep 1 at 13:45
    
Hundreds of retroviruses are normally found in healthy human beings. So the question is, if retroviruses are cytotoxic or it depends on the classification? Should the question 'Does all retroviruses are cytotoxic?' would be more clear? Or 'which'? –  kenorb Sep 1 at 13:49
    
Re-phrased the question to opposite, so I think it's more clear. –  kenorb Sep 1 at 13:52
    
The word cytotoxic in your question probably came from 'cytotoxic t cell'. Programmed cell death induced by a cytotoxic t cell is responsible for cytotoxicity, not the retrovirus itself. –  mattkaeo Sep 3 at 19:36
    
Wiki says that cytotoxicity is the quality of being toxic to cells, so it's not only refered to T cells as far as I understand, but to all other natural killer cells. Please correct me if I'm wrong. –  kenorb Sep 4 at 10:49

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up vote 7 down vote accepted

As you point out human beings (and other organisms) have hundreds of retroviruses and many can be seen in the human genome, some of which appear to be the remains of deactivated viruses, others which may be active. Most retroviruses are not pathogenic - they don't cause disease.

This is because many retroviruses replicate slowly, budding and secreting from the cell surface in small numbers without killing their host cell.

There are several disease-causing retroviruses. Human T-cell Leukemia Virus (HTLV) can cause T-cells to replicate in an uncontrolled fashion, resulting in leukemia. This is not a necessary result for HTLV to replicate, but it is a result of viral infection as viral replication tweaks the cell machinery to replicate.

While it's not clear exactly how, Human Immunodeficiency Virus (HIV) kills its hosts cells. Unfortunately HIV's hosts are CD4 immune cells. The fact that sporadic replication of HIV can cause all host immune cells to die entirely makes HIV a pathogen.

Disease is usually thought of as a lack of adaptation of a pathogen and host: viruses do better if they do not kill their host. Both these cases are possibly not the future for either virus: either could adapt to reproduce without causing a disease. Or they might have already , having spun off some strains into the pool of quiet retroviruses medical science does not concern itself with.

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I'm going to down vote your answer you shouldn't hav +5 with 0 on the question –  caseyr547 Sep 2 at 10:40
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This answer gives a good background for how retro viruses may differentially damage biological function. The word cytotoxic in the question wasn't appropriate for the relationship between a cell and a virus. –  mattkaeo Sep 3 at 19:21
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@caseyr547 The upvote for the answer only says something about the quality of the answer. So even if the question doesn't make much sense it can still be possible that the answer is good. What is the case here. –  Chris Sep 17 at 14:53

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