Given the psychologisers emphasis on triggering and maintaining aspects of CFS, even of MRVs are only an opportunistic infection, they could also be the cause of CFS.
In many way CFS seems to be an opportunistic disease. Many people came down with CFS following glandular fever. If MRVs were an opportunistic infection that took advantage of the damge done by EBV and then prevented a normal recovery, then they would have caused CFS.
I thought about this too, and i think an initial environmental factor (which include infections) first has to suppress an effective Th1 immune response in the host to enable XMRV to infect that person and start to cause immune dysfunction on its own.
I have another study, which is rather complicated and technical, but very powerful. they have studied a large range of different cytokines and their expression in relation to each other. Results show that cfs patients have attenuated Th1 and Th17 immune response. Th1 is a T-cell response that is necessary to overcome/resist viral infection. Th1 cells, when activated, secrete Th1 cytokines of which IFN (interferones: alpha, bta, gamma), IL-2 and IL-12 are important members. IFNs activate antiviral responses in neighboring cells called the IFN pathway. This pathway includes RNAseL, which normally degrades viral RNA, hostcell mRNA, and induces apoptosis of the infected cell. This apoptosis prevents the virus from further replicating in that cell and causes the cell (with the virus) to be cleared by macrophages. As we know CFS has been linked to RNAseL dysfunction and to a Th1 to Th2 shift in immune response. Th2 cytokines, expressed in increased amounts in cfs, inhibit development of Th1 cells and an Th1 immune response. Th17 is another activated T-cell subset which should clear (intracellular) infection. I'm not familiar with Th17 and it is an T-cell subset in which much research still has to be done.
XMRV is sensitive to IFN partway responses, which could both explain why not everyone gets XMRV (and cfs) and why we would be sensitive to this virus. This would however imply that immune dysfunction precedes XMRV infection. although this is not impossible, i personally think that temporary immune suppression by environmental factors during first XMRV infection would be sufficient to cause chronic infection. Once XMRV is established in immune cells it can perform immune suppression on its own and maintain immune dysfunction for as long as the infection is present.
-Silverman, R. H. et al. Nat. Rev. Urol. advance online publication 1 June 2010; doi:10.1038/nrurol.2010.77
-In Vivo. 2005 Nov-Dec;19(6):1013-21.
Impairments of the 2-5A synthetase/RNase L pathway in chronic fatigue syndrome.
Nijs J, De Meirleir K.
Department of Human Physiology, Faculty of Physical Education and Physiotherapy, Vrije Universiteit Brussel, Brussels, Belgium.
Abstract
This paper provides an overview of the evidence addressing the impairments of the 2'-5' oligoadenylate (2-5 A) synthetase/RNase L pathway in Chronic Fatigue Syndrome (CFS) patients. The 2-5A synthetase/RNase L pathway in CFS patients appears to be both up-regulated (i.e. increased levels of bioactive 2-5A synthetase and increased activity of the RNase L enzyme) and deregulated (elastase and calpain initiate 83 kDa RNase L proteolysis, generating two major fragments with molecular masses of 37 and 30 kDa, respectively). The deregulation of the 2-5A synthetase/RNase L pathway in CFS accompanies decreased NK-function and deregulation of apoptotic pathways. Since various components of the pathway appear to be related to performance during a graded exercise stress test, some evidence supportive of the clinical importance of the impaired pathway in CFS patients has been provided. Studies addressing the treatment of the deregulation of the 2-5A synthetase/RNase L pathway in CFS are warranted.
PMID: 16277015 [PubMed - indexed for MEDLINE]
-1. Brain Behav Immun. 2010 May 4. [Epub ahead of print]
A formal analysis of cytokine networks in Chronic Fatigue Syndrome.
Broderick G, Fuite J, Kreitz A, Vernon SD, Klimas N, Fletcher MA.
Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
Chronic Fatigue Syndrome (CFS) is a complex illness affecting 4 million Americans
for which no characteristic lesion has been identified. Instead of searching for
a deficiency in any single marker, we propose that CFS is associated with a
profound imbalance in the regulation of immune function forcing a departure from
standard pre-programmed responses. To identify these imbalances we apply network
analysis to the co-expression of 16 cytokines in CFS subjects and healthy
controls. Concentrations of IL-1a, 1b, 2, 4, 5, 6, 8, 10, 12, 13, 15, 17 and 23,
IFN-gamma, lymphotoxin-alpha (LT-alpha) and TNF-alpha were measured in the plasma
of 40 female CFS and 59 case-matched controls. Cytokine co-expression networks
were constructed from the pair-wise mutual information (MI) patterns found within
each subject group. These networks differed in topology significantly more than
expected by chance with the CFS network being more hub-like in design. Analysis
of local modularity isolated statistically distinct cytokine communities
recognizable as pre-programmed immune functional components. These showed highly
attenuated Th1 and Th17 immune responses in CFS. High Th2 marker expression but
weak interaction patterns pointed to an established Th2 inflammatory milieu.
Similarly, altered associations in CFS provided indirect evidence of diminished
NK cell responsiveness to IL-12 and LT-alpha stimulus. These observations are
consistent with several processes active in latent viral infection and would not
have been uncovered by assessing marker expression alone. Furthermore this
analysis identifies key sub-networks such as IL-2:IFN-gamma:TNF-alpha that might
be targeted in restoring normal immune function.
PMID: 20447453 [PubMed - as supplied by publisher]
I think either the original PNAS paper or the FDA Q&A session for the press (on the FDA website) shows either Lo or Alter specifically using the word 'infected'. Sorry too knackered to go and check the original articles/press interviews just now!
The original Science paper too included several lines of evidence that they where not only detecting a virus that had infected CFS patients, but also that viral proteins where expressed in blood cells (which only occurs when the virus is actively replicating in the cells) and that infetious viral particles where present in the blood (they where able to infect a human cell line).