Okay, I have written a LOT about the connection between wayward ERV activity and Multiple Sclerosis. This is something scientists have been investigating for a long time… but we still do not know exactly what is going on.
It seems the running hypothesis is that ‘something’/’somethings’ alter the epigenetic profile of individuals DNA, allowing for expression of an endogenous retroviral Envelope protein, especially in the brains of (future) MS patients. These proteins are pro-inflammatory, start causing all sorts of trouble, like MS.
Its gotten to the point where other scientists are trying anti-ERV-Env therapies to fight MS.
But, we still dont *know* this chain of events is what is leading to MS, or that targeting Env expressing cells would stop MS.
A lot of the ERV–>MS papers are looking at ERV expression in the blood cells of MS patients. That has *really* bothered me. Why would someones CD8+ T-cells tell you anything about what is going on in their brains?
But, I fully understand that brains are not as easy to study as blood.
In this paper, however, they looked at the brains of MS patients and controls.
There was no difference in ERV expression between MS patients and controls.
The data was all over. Some MS patients had some ERV expression up, and other ERVs were down. And some ERV expression was up compared to some controls, but equal to other controls. They called it “interindividual variation regarding overall and locus-specific HERV-W transcript levels”.
It still might have nothing to do with the ERV Env proteins. The presence of the proteins might be an artifact of the ERV LTR (promoter) activity. Because this paper did note that the LTRs associated with the ERVs associated with MS retain promoter activity in both directions (think of it as a book you can read forwards and backwards), even if they arent perfect LTRs (mutations).
Maybe its not the ERVs in the genome, but the stuff around the ERVs that are being expressed inappropriately that are causing trouble?
What a mess.
Though we have learned a *lot* about ERVs–>MS, we are still where we were at when I wrote about this in 2009:
Active ERV proteins could be a cause of MS, an effect of the cause of MS, or an effect of a cause that ends up perpetuating MS.
Bonus for those of you familiar with the XMRV fiasco– In 1997, a paper in PNAS reported they found a novel retrovirus in Multiple Sclerosis patients, MSRV. This current paper says those ‘novel retroviral sequences’ were really just recombination in sequencing of ERVs. Totally an artifact, not ‘real’. Yup…