Why viruses, immunoevasins and mixed Infections may make ME CFS too complex and variable to be easily understood.
I have always believed viruses are important contributors to ME CFS because of my own experiences but to be honest research has not been going smoothly, there have been a couple of high profile disappointments lately but also some good news on the horizon.
In the UK affymetrix studies seeking patterns of gene activation in ME CFS ran into a problem. While discovering real differences between ME CFS patients and normals they also showed that no consistent pattern could be found. The variability between patients seems to have been too great for the small sample size of about 50 patients. But in science a negative result is still a result and people have learned from this. Professor Stephen Holgate since suggested there may be as many as 15 different subtypes of ME CFS. Personally, for reasons set out below, I think that may be a conservative estimate.
The attempt to find a single causal virus was on the face of it set back with the discovery that XMRV was not reliably detected in association with ME CFS, carefully disproved by Professor Ian Lipkin using a double blind experimental protocol. Fortunately Professor Lipkin and colleague Mady Hornig have taken over the reins and are undertaking some very ambitious studies in the USA which have learned from the difficulties with small sample sizes and look very promising with expanded studies in planning. FYI They need and deserve our financial support.
Other fields of virology have also been progressing. Over the last two decades an intriguing picture of how viruses evade human immunity has begun to emerge. As a humble zoology grad I have tried to keep up with aspects of this research which may be relevant to my own condition and I relate discoveries here which are of particular interest to me in the attempt to understand my own illness in the hope that they may be of interest to others.
One of the commonest of the viruses studied is Epstein Barr Virus, EBV for short, which can cause glandular fever aka mononucleosis when contracted in adolescence or later in life and is present in 95% of the population. EBV is a herpes virus which effects different people differently and has frequently been implicated in cases of ME CFS and is known for its ability to persist in and disrupt the immune system causing severe illness in a small number of people (see Dr Lerner on herpes virus induced CFS). It used to be thought that ME CFS was often caused by chronic EBV, but the discovery of ME CFS cases where EBV was apparently not present cast doubt on that interpretation.
There may be more to EBV than meets the eye however since recent evidence (discussed a bit here and in more detail at Simmaron Research) suggests that some ME CFS patients have a compromised immune response to EBV. Somehow their immune cells forget how to mount an immune response to EBV leading to higher rates of latent EBV replication and lowered ability to deal with EBV reactivation. So by some measures (i.e. assessing the immune response to EBV as a way to decide if EBV is present,) it can appear that EBV is not present, when really it is!
In any case, logic suggests that even if some cases of ME CFS are not caused by EBV this does not mean that no cases are caused by it, as one cannot rule out the possibility that EBV causes a proportion of ME CFS and other viruses cause a proportion of other cases. Since XMRV has been disproved, it is easier to say that assuming one singular pathogen is responsible for ME may be a mistake. This may seem a bit vague so one reason for discussing immunoevasins here is to look at why this is a very real possibility.
In the intervening period since ME CFS research turned away from chronic EBV, research of EBV which is also implicated in cancer and autoimmune disease has uncovered how EBV can evade the human immune system by making products which jam our defences. These products are called immunoevasins and we are still learning how they work. We have also learned that other viruses can likewise make comparable immunoevasins which attack the same weaknesses in the human immune system. Below are discussions of two examples, EBV's viral version of interleukin-10 and EBV's BNLF2a gene, an antigen processing blocker.
I must stress at this point, proof conclusively linking or debunking the action of immunoevasins in relation to ME CFS symptoms has not been acquired, this blog is speculation. However the known effects of some of these immunoevasins bear comparison with ME CFS symptoms. Thus far, the more we learn the more credible the scenario is becoming not only that a virus like EBV could cause the primary immunological symptoms of ME CFS but that other viruses and possibly biotic bugs can too, by attacking the same weaknesses in human immunity.
One of EBV's immunoevasins, a secret weapon which has been known about for over two decades now, is a molecule which mimics a human immune messenger molecule called interleukin-10 or IL-10 for short. Viral versions are known as viral interleukin-10 or vIL-10.
After much careful research we now know EBV's version of vIL-10 can effect the human immune system and release cytokines which encourage allergic and autoimmune reactions as well as reduce antiviral activity (as linked above). This matches the TH2 shift observed by Dr Paul Cheney in his ME CFS / CFIDS patients, which people commonly report as part of their ME and which has experimental corroboration. Dr Cheney has specifically discussed the way in which pathogens mimic IL-10 as a possible cause of TH2 shift in ME CFS patients.
The main effect of EBV's vIL-10 is to change the activity of defensive white blood cells making it easier for EBV to survive. EBV predominantly survives as a persistant infection inside white B cells which by means of other immunoevasins it activates and transforms prematurely into long lived memory B cells inside which it can persist, though it does infect other cell types. This is interesting because these are the very same B cells which are wiped out by rituximab treatment which we know helped some ME patients in Norway.
On the other hand vIL-10 makes NK (natural killer) cells less active. NK cells are an important immune defence against many pathogens and they have been shown to be less active than normal in some CFS studies (eg Brenu). vIL-10 also decreases the activity of CD4+ T helper cells which normally produce cytokines which activate NK cells.
If EBV reactivates and infects new cells it produces more immunoevasins including vIL-10, which must pass into the intercellular medium to have its effect and in so doing can spread around the whole body causing system wide changes. EBV is using vIL-10 to prevent NK cells from destroying the cells it has infected. By doing this it also makes its human host more vulnerable to other bugs which NK cells would otherwise kill.
This is a wide range of bugs including yeasts and biotic infections because NK cells are thought to be essentially innate killers, not specifically attacking a particular type of antigen like B cells or T cells, they simply eat anything which is not showing "self" antigens. So NK activity is stopped by a self antigen not started by a bug antigen. Not surprisingly the immune system has a failsafe to regulate NK cell activity to stop it accidentally eating its owner's body and that failsafe is IL-10. vIL-10 can do many of the same things as IL-10 and as a result NK cell suppression occurs with every reactivation episode of EBV. Each cycle the host immune system would be laid low for a while as is often reported in cases of ME and yet different aspects of the immune system like B cell transformation can be stimulated by the very same virus. I can only speculate at this stage that where EBV reactivation was continual, NK deactivation probably would be too. Alternatively both could vary in intensity over time through periodic bouts, which matches the experiences of some patients.
Speculatively speaking this fits some aspects of the altered immune response in ME CFS I have experienced which has been corroborrated anecdotally by many other people; i.e. a poor response to some biotic infections at certain times, vulnerability to virus infections and an altered inflammatory response to them, also raised allergies and tendency to rheumatic joint pain, which could all be explained by the effects of vIL-10.
TAP inhibitors: how EBV's gene "BNLF2a" silences infected cells.
Another more recently understood secret weapon of EBV is made by a gene called BNLF2a. Once inside the cell, one of the first things EBV does, as well as making vIL-10, is making the product of the BNLF2a gene which stops the cell being disposed of by white cells. These particular white cells for the record are CD8+ killer T cells which, unlike NK cells, can target specific bug antigens presented on the outside of cells and select infected cells for demolition.
To do this EBV exploits an Achilles heel of the immune system which is that an infected cell must alert white T cells waiting outside to consume infected cells. It may seem a bit burocratic, but unless the infected cell reports properly the white T cells cannot sense what is going on inside the infected cell because the cell membrane gets in the way. The infected cell makes its report by moving virus antigens inside the cell through the membrane to the outside, to act as flags, using a special "transporter associated with antigen processing" or "TAP" for short. EBV's secret weapon, the BNLF2a gene, "turns off" TAP and prevents flags from being raised, so the CD8+ killer T cells outside cannot tell anything is wrong.
Its like a baddie in a movie kidnapping someone and tying a gag over their mouth so they cannot cry out, in this way the EBV can hold a cell hostage and live inside it for a long time, occasionally reactivating to provoke another "bad patch" and infect more cells and other people. This allows these viruses to maintain an infection in a host for longer and thereby spread themselves to others. This is probably why NK cells evolved in the first place, as a failsafe, since a cell which does not have functioning TAP will also not present the self flags which appease NK cells, so NK cells should eat them once their existing self flags are recycled. But this failsafe relies on active NK cells and as already mentioned EBV does its best to deactivate NK cells with vIL-10.
So EBV inflicts a double whammy on the immune system, disabling key defences both inside and outside cells, which is probably why it is such a common virus. Luckily for us a virus as successful as that evolves over time by natural selection to become less fatal, simply because if it kills its host it dies too and cannot spread. That doesn't stop it making the host very unwell, but it might explain why a host with ME CFS could be so unwell for so long and yet not die. Viruses would evolve to do exactly that.
Again EBV is not the only virus which can turn off TAP. For example the common herpes simplex viruses HSV I & II make ICP47 (1 & 2) both block TAP inside the cell. Cowpox virus CPXV12 blocks TAP, so does US6 from human cytomegalovirus, so does UL49.5 from varicellovirus. All of these viruses can disable TAP, yet the less closely related species of virus evolved convergently to do it in different ways suggesting that disabling TAP is highly advantageous to viruses and implying that TAP is both a central mechanism in anti-viral defence and because of this also an Achilles heel, a key weakness in our immune defence like IL-10, only inside cells instead of outside them.
It takes little imagination to conceive that the combination of vIL-10 and TAP inhibitors could be very disruptive to the effective clearance of infections by the human immune system resulting in the kind of ongoing low level infection which could cause chronic immune activation which is typical in ME CFS cases.
Personally I think this really is relevant because of my own experience with ME CFS, which began some time after a severe adolescent EBV infection and yet involved other recurrent viruses which were not EBV itself.
Are Immunoevasins the answer?
Its too early to say. If we learned anything from XMRV surely it was to be cautious about this kind of complex biochemistry and raising hopes without quadruple checking the evidence. Experiments are needed to prove or disprove any hypothesis. Yet the discovery of these immunoevasins has the potential to explain many perplexing yet common ME CFS (CFIDS type) symptoms in one go, so they need to be looked at and understood better.
However its worth pointing out that if we hypothesise immunoevasins may play a part and accept the apparent absence of EBV in some cases of ME CFS might be misleading, looking for one single virus to blame for all ME CFS would still be a mistake. The reality emerging from immunoevasin research is that EBV is not alone in using viral Interleukin-10 or TAP inhibitors to trick the immune system.
Cytomegalovirus for example also produces a viral version of Interleukin-10 (as does Orf Poxvirus which humans can catch from sheep and so does equine herpes virus type 2 "EHV-2" for short, see paragraph 3 of the introduction). They are probably not alone because IL-10 represents a weak point in human immune defences as it deactivates key immune responses. CMV also produces a TAP inhibitor and is not alone, (as linked above see fig5 p578).
It makes sense that any viruses which acquired a copy of the IL-10 gene or of a viral forgery would tend to survive and remain with us. In evolutionary terms the selection pressure favouring the use of vIL-10 is very great. This might also apply to some biotic infections which could also benefit from making counterfeit IL-10 because of the way it reduces NK cell activity. Likewise any virus which can disable TAP has an advantage and will persist better than one which cannot. This implies there may be more viruses using these tricks and that a range of different infections could impact our immune systems in similar ways ie deactivating NK cells, activating allergies, promoting autoimmune disease with persistent relapsing remitting intracellular infection causing periodic or chronic immune activation. In a nutshell, ME CFS.
Experts like Dr Jonathan Kerr and Prof Stephen Holgate have stated that there are probably many subtypes of ME based in part on empirical evidence from affymetrix studies as well as clinical experience. Certainly there is a lot of variation between different cases which I discuss in more detail in a section below but this makes it all the more plausible that vIL-10 producing pathogens may account for some ME CFS subtypes.
Speculation on Mixed Infections.
Immunoevasins are significant for mixed infections because they explain how two or more viruses might interact with each other inside their host, raising the possibility that more than one kind of virus is involved in individual cases of ME CFS through unfortunate combinations. (Something I have tried hard to understand because of my own case history involving mixed infection with recurrent viruses.)
One study on both EBV and CMV provides an example of how viruses can interact with each other, showing that where elderly people have both EBV and CMV they are more likely to experience inflammatory disease from their EBV infection if CMV is present. This suggests EBV and CMV interact within the patients' bodies making the combination more harmful than either one on its own. The same may be true of interactions between other viruses.
At this point, what we know raises more questions than it answers. A finger of suspicion points at EBV because of the way that it can make itself at home in B cells and turn their activity to suit itself using immunoevasins.
But 95% of the population has EBV and they dont all get ME CFS. We know that if you get it young it barely causes a snuffle, but in your teens it can put you in bed for months because you are better able to fight EBV the younger you are. It also varies for individuals, some people are not badly affected by it, others are. Broadly speaking the fact that EBV does affect people so differently makes it more plausible that it could be behind some cases of ME CFS.
We also know CMV's immunoevasins grant it some abilities similar to EBV's, enabling it to disable the immune system and become a persistant infection. Again it is a common virus and not everyone with it has ME CFS but these are two viruses we know more about than many others so are good examples to discuss, even though we are left wondering what else is going on and how many more can do likewise.
The possibility worth exploring is that where one virus like EBV or CMV can disable the NK response, other viruses which can't do this themselves can take advantage of that to infect cells elsewhere in the body in different tissues, to which they are specifically adapted.
This alone could make mixed infection more severe than you would expect judging by the sum of the affects of individual viruses. One reason for this is that viruses adapt to their host and a successful virus does not kill its host as this reduces the time they have to spread themselves. Viruses tend to evolve to balance their "aggression" to be sufficient to survive and spread and no more. It is only when viruses switch hosts that they tend to become lethal plagues until the virus evolves and its lethal affects attenuate.
However where a virus is disabling an aspect of a host's immune system not targeted by a second virus which is sufficiently aggressive to survive in a healthy person, the second virus may prove overly aggressive for an immune system already compromised by the activity of another virus. So a combination of viruses may cause greater debility than one virus on its own.
Evolutionarily speaking this could happen and keep on happening where mixed infections of a particular combination which is unfortunate for the host are relatively rare events compared to the total number of infections by those viruses in the whole population. This is because a virus will primarily evolve to suit the most common infection scenario, since that is the way it will normally spread.
What we may be seeing with the rising incidence of ME CFS like illness is a reflection of the increased chance of getting an unfortunate mixed infection in the modern world. This could be due to increase in travel, especially air travel as well as the total size of the human population of the world.
A further discussion, which is speculation at this point, is that where secondary viruses can disable TAP, the compromised cells may become a refuge for any viruses which can infect them including vIL-10 producing viruses. This might allow this kind of illness to become not only persistant but progressive, acting like a ratchet of infection, claiming more and more host cells for the viruses to live in as the infection continues. This deserves consideration with respect to more severe ME CFS cases.
I believe this line of thought could be significant for understanding ME CFS because of my own experience with at least two viral infections which I believe interacted with each other resulting in ME CFS with recurrent viruses.
There are other alternative hypotheses. For now they are all just hypotheses. There could still be one virus like the one we hoped XMRV would be, but then you have to explain the wide variation in gene activity seen in the London affymetrix studies. The cause of ME CFS might even be a new kind of disease, like prion disease, which we simply haven't encountered before. We still can't rule these out but for now the interaction of viruses using immunoevasins is a sufficient hypothesis, employing facts we do know and the best I can currently find, to explain what happened to me, though it remains to be seen if this is the real cause for the millions of people who are afflicted around the world.
Speculation on Variability in ME CFS.
The variation among ME CFS patients presents a puzzle which mixed infections and their immunoevasins might explain, but for now we don't know for sure what proportion of variation this would account for.
vIL-10 suppresses NK cells, stimulates B cells and has the potential to encourage autoimmune illness which could cause even more clinical variation in symptoms between different patients, even when caused by the same infection, because antigen specific immune reactions are by their very nature a dice throw and so if they happen to cause autoimmune disease can affect any part of the living body due to the way the immune system creates random antibodies in its search for a way to destroy invaders.
There is a theory that EBV in particular contributes to autoimmune disease by making autoimmune cell lines of B cells, which should die off, into long lived memory B cells. These normally act as parent cells to clones of cells intended to fight specific pathogens. Where the B cell is accidentally attacking the body it is normally disposed of, but if infected by EBV they can be incorrectly confirmed as a bonafide defender leading to the production of a clone army of B cells causing autoimmune disease in whatever tissue they happen to be specific to, which is completely random. This might contribute to autoimmune reactions in some ME CFS patients, as the Norwegian rituximab trials suggest it does.
This implies there may be at least two sources of variability involved in ME. Firstly a large number of different virus combinations, secondly the random chance of autoimmune reactions. This is without considering the genetic variability of individuals, which constitutes a third kind of variability which could alter the course of the disease.
Timing is also known to make a difference to the course of viral infections. As previously mentioned, EBV for example is often much more severe when contracted by a teenager than by a baby. When an individual contracts viruses, relative to life history and events like contracting other viruses, may make all the difference in how mixed infections play out for different individuals.
Besides this the disease itself is known to change over time both in the long term and for some people in the short term creating cycles of fluctuating illness. So the assessment of patients and their biochemistry can show variability for that reason as well, making it all the more difficult for clinicians and experimenters to spot patterns and join the dots.
Solving the Riddle.
The implication of viruses evolving strategies which converge on weak points in the human immune system and the possibility of mixed infection in ME CFS is that epidemiologists studying outbreaks may be looking at intricate complexity, not necessarily a simple disease caused by a single infection. For example when looking at an ME outbreak they may be looking at the intersection between epidemics of two or more different viruses, each seeming relatively innocuous on its own, in the context of individual differences in susceptibility caused by genetics and timing.
It is possible to conceive that we are in a situation where variability means that two patients with exactly the same condition might provide different biochemical results at any given moment in time despite having comparable clinical histories. This would imply that in order to understand ME CFS, which we don't, we need to discern relevant patterns of biomarkers for the disease over time as well as between different subtypes. It may be one of those situations where small efficient studies really won't get the relevant information and bigger really is going to be better.
Noone does bigger better than the USA and Prof Lipkin and colleague Mady Hornig are already embarked on this process (as linked above).
This will hopefully lay the groundwork for identifying and characterising immunoevasins and the way they affect our human immune systems and in my opinion this will eventually lead to an understanding of ME CFS.
If there is anyone who can make headway in this field of study it is Ian Lipkin (wiki) the professor who proved that XMRV was not the answer to ME CFS. He and his expert team have a good reputation for using effective biochemical analytical tools, using careful experimental protocols, to identify viruses involved in epidemics.
He is already working on identifying viruses in white blood cells in ME CFS, which is good news to say the least and has suggested a worthwhile next step on the journey to understanding ME CFS, along with many other human diseases, would be to map the molecular fingerprints of the human microbiome, all the microscopic symbionts and pathogens which live within us, which we know very little about.
He has made a heartfelt plea for ME CFS patients to support this ambitious project to sequence the entire microbiome in order to lay the foundation for future research.
Its a big project and needs at least a million dollars to get it started. By crowdfunding standards this is very achievable, if 100,000 people gave $10 each that would do it! Once completed it would put him and the rest of the scientific community in a better position to detect immunoevasins and other patterns of activity in pathogens linked to disease of all kinds.
Considering the realpolitik of ME research, supporting this project would also make a visible statement, that the ME CFS community are self-empowered, are serious about finding out the truth and want to help those who want to help us. By funding this work we can not only advertise our cause but we can ensure that this knowledge is applied as quickly as possible to understanding ME CFS. Besides enlightened self interest this work will benefit all humanity and noble as that is, it also lays down a marker in an important conversation about enlightened mutual interest and why the disabled and impoverished ME CFS patient community has been left to fend for itself when a percentage of all healthy people in the developed world will be joining our number every year until the cures are found.
It is an historic opportunity for the ME CFS community to contribute to their own future and the future of humanity. Like the sequencing of the human genome, it is a great undertaking which will help spur advances in technical know how and understanding benefiting medical research across the board and far into the future.
If we are remembered for nothing else, completing this project would be something to be proud of.
To quote Eleanor Roosevelt, "it is better to light a candle than to curse the dark." Lets beat this thing together, it has got to be worth $10.