1. YBRBI 1806 No. of Pages 8, Model 5G
9 July 2011
Brain, Behavior, and Immunity xxx (2011) xxx–xxx
1
Contents lists available at ScienceDirect
Brain, Behavior, and Immunity
journal homepage: www.elsevier.com/locate/ybrbi
2 Review
3 Chronic fatigue syndrome, the immune system and viral infection
4 A.S. Bansal a,⇑, A.S. Bradley a, K.N. Bishop b, S. Kiani c, B. Ford a
5 a
Dept. of Immunology, Epsom and St. Helier University Hospitals NHS Trust, Carshalton, Surrey, SM5 1AA and Chronic Illness Research Team, Stratford
6 Campus, University of East London, London E15 4LZ, UK
7 b
Division of Virology, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, UK
8 c
Dept. of Immunology, Kings College Hospital, Denmark Hill London, UK
9
10
a r t i c l e i n f o a b s t r a c t
1 2
2 6
13 Article history: The chronic fatigue syndrome (CFS), as defined by recent criteria, is a heterogeneous disorder with a com- 27
14 Received 8 April 2011 mon set of symptoms that often either follows a viral infection or a period of stress. Despite many years of 28
15 Received in revised form 14 June 2011 intense investigation there is little consensus on the presence, nature and degree of immune dysfunction 29
16 Accepted 28 June 2011
in this condition. However, slightly increased parameters of inflammation and pro-inflammatory cyto- 30
17 Available online xxxx
kines such as interleukin (IL) 1, IL6 and tumour necrosis factor (TNF) a are likely present. Additionally, 31
impaired natural killer cell function appears evident. Alterations in T cell numbers have been described 32
18 Keywords:
by some and not others. While the prevalence of positive serology for the common herpes viruses appears 33
19 Chronic fatigue syndrome
20 Cytokines
no different from healthy controls, there is some evidence of viral persistence and inadequate contain- 34
21 T cells ment of viral replication. The ability of certain herpes viruses to impair the development of T cell memory 35
22 NK cells may explain this viral persistence and the continuation of symptoms. New therapies based on this under- 36
23 Immune memory standing are more likely to produce benefit than current methods. 37
24 Viruses Ó 2011 Published by Elsevier Inc. 38
25
39
40
41 1. Introduction The diagnosis of CFS presently rests on the exclusion of any 63
medical or psychiatric causes of fatigue in someone with new on- 64
42 The chronic fatigue syndrome (CFS) is characterised by severe set persistent tiredness for over six months. In 1988 Holmes et al. 65
43 and disabling fatigue (Afari and Buchwald, 2003) but without a from the US Centre for Disease Control (CDC) drafted the working 66
44 patho-physiologic explanation. In addition to fatigue, individuals case definition for CFS to help standardise the patient population 67
45 with CFS also report a variety of other symptoms including muscu- for research purposes and to avoid the connection with viral infec- 68
46 loskeletal pain, sleep disturbance, impairment in short term mem- tion after investigations failed to confirm past or current infections. 69
47 ory and concentration, sore throat, and headaches of new type, A 1994 revision of the CDC case definition constitutes the current 70
48 pattern and severity (Reid et al., 2000; Afari and Buchwald, criteria for chronic fatigue syndrome and is the most widely used 71
49 2003). In nearly all cases there is an exacerbation of these symp- definition internationally (Fukuda et al., 1994). Amendments have 72
50 toms, but particularly the fatigue by any form of physical, mental been proposed since and the Canadian criteria that highlight the 73
51 and sometimes emotional exertion. Symptom severity may also importance of a post-exertional malaise have gained some favour 74
52 fluctuate on a daily or weekly basis without obvious cause. (Carruthers et al., 2003). Nevertheless, problems remain in case 75
53 Studies of the general population suggest a prevalence rate for definition and the clear influence that differing criteria may have 76
54 CFS of between 0.2% and 2.6% depending on the criteria used (Reid on research results (Christley et al., 2010). 77
55 et al., 2000; Afari and Buchwald, 2003). Most of the research on CFS has long been thought as having a significant immunologi- 78
56 prognosis and treatment outcome has focussed on people attend- cal component. This is because of the nature of the symptoms and 79
57 ing specialist centres, who may be assumed to have more severe the finding of abnormalities in the immune system. However, it is 80
58 and complex difficulties. Nevertheless, studies suggest that a sig- still not clear whether these defects are the cause or the result of 81
59 nificant proportion of people with CFS will continue to experience CFS. What is clear though is that therapies that modulate the im- 82
60 symptoms for some time (Afari and Buchwald, 2003). Indeed, as mune system can result in a clinical improvement. This review will 83
61 few as 6% of people with CFS return to pre-morbid levels of func- focus on the role of impaired immunological memory in CFS, with 84
62 tioning in the medium to long term (Reid et al., 2000). particular reference to viral infections and possible therapeutic 85
interventions. It should, however, be noted that the immune sys- 86
tem is significantly influenced by stress, mood and by disturbance 87
⇑ Corresponding author. Fax: +44 208 641 9193. of sleep. Varying degrees dysfunction in these areas may initiate or 88
E-mail address: Amolak.Bansal@ESTH.nhs.uk (A.S. Bansal). perpetuate immune changes that contribute to a susceptibility to 89
0889-1591/$ - see front matter Ó 2011 Published by Elsevier Inc.
doi:10.1016/j.bbi.2011.06.016
Please cite this article in press as: Bansal, A.S., et al. Chronic fatigue syndrome, the immune system and viral infection. Brain Behav. Immun. (2011),
doi:10.1016/j.bbi.2011.06.016

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90 severe or prolonged viral infection and the development of CFS jects with major depression, lupus and multiple sclerosis 150
91 (Fig. 1). (Bennett et al., 1997). 151
In women with CFS, abnormalities of interleukin (IL) 1b and 152
IL1Ra release by peripheral blood mononuclear cells (PBMC) were 153
92 2. Heterogeneity of CFS in relationship to immune dysfunction demonstrated particularly in the premenstrual phase (Cannon 154
et al., 1997). However, no difference in IL1b was evident in the 155
93 Persistent fatigue lasting more than 6 months may be observed peripheral blood of CFS patients undergoing sub-maximal and self 156
94 in several viral and bacterial infections and in numerous rheuma- paced exercise (Nijs et al., 2010). While IL1b and IL6 assessed by 157
95 tological conditions. Previous investigations of the biochemical, multiplex technology were raised in the CFS patients reported by 158
96 microbiological and immunological abnormalities in subjects with (Fletcher et al., 2009), the level of TNFa was no different from 159
97 CFS have often considered CFS to be a single disorder. The problem the healthy controls. Confusingly, there was a mixed elevation of 160
98 is compounded by difficulties in diagnosing this condition which is Th1 and Th2 cytokines and no alteration in the Th17 and T regula- 161
99 primarily one of exclusion. This may explain the absence of any tory cell associated cytokines. 162
100 consistent set of abnormalities in this group of people. Even com- In a large study of well characterised patients with CFS, (Raison 163
101 paring subjects with acute onset CFS with those whose symptoms et al., 2009) found highly sensitive CRP to be no different from con- 164
102 had a gradual onset confirms significant differences in premorbid trols when adjusted for age, sex, race, location of residence, body 165
103 personality, prognosis and response to treatment (Masuda et al., mass index (BMI), depressive status and immune-modulating 166
104 2002a,b). There also appears to be differences in the levels of cer- medications. Interestingly, depressive symptoms were associated 167
105 tain immune parameters depending on the mode of onset of the with increased log hs-CRP. IL6 was also found to be similar in 168
106 CFS symptoms (Masuda et al., 2002a,b). Thus dividing patients on CFS versus controls when BMI was taken into account by (Nater 169
107 the basis of their Natural Killer (NK) cell function appears to select et al., 2008). In our own unpublished work we have observed no 170
108 a subgroup of individuals who may respond favourably to immune significant or consistent change in the level of plasma IL1b, IL6 171
109 based therapy using interferon alpha (See and Tilles, 1996). There- and TNFa when measured at 3 month intervals in patients with 172
110 fore it is important that subjects with CFS are not grouped into a CFS and when correlated with degree of fatigue. A similar lack of 173
111 single entity based simply on a common set of symptoms. At the variation within individuals in mitogen stimulated cytokine pro- 174
112 very least they should be divided into those with an acute versus duction has also been seen in girls with severe fatigue, amongst 175
113 gradual onset symptoms and those with and without abnormality whom those with CFS had an increased profile of anti-inflamma- 176
114 of immune function. In the absence of such a division inconsistent tory cytokines and reduced inflammatory cytokines (ter Wolbeek 177
115 results may be evident in regard to precipitating factors, prognosis et al., 2007). 178
116 and response to specific therapies. (Natelson et al., 2002) drew Regarding the immune stimulatory and regulatory cytokines, 179
117 attention to this problem several years ago in relationship to the lipopolysaccharide (LPS)-induced IL10 secretion in whole blood 180
118 immune system and summarised the inconsistency in the results cultures was significantly increased in patients with CFS compared 181
119 obtained by several groups. with controls and with a trend to decreased IL-12. Importantly, this 182
IL10 secretion appeared to be resistant to suppression by dexa- 183
methasone in the CFS patients only (Visser et al., 2001) although 184
120 3. Cytokine dysregulation in a later study this group found IL10 secretion to be no different 185
from the control group. A slightly increased level of IL10 has also 186
121 Despite the heterogeneity in CFS, there is growing evidence sug- been observed in CFS patients with and without fibromyalgia com- 187
122 gesting immune dysfunction plays an important role in CFS (Patar- pared to healthy controls during sleep by (Nakamura et al., 2010). 188
123 ca-Montero et al., 2001; Stewart et al., 2003). However, the past However, there was no difference in the pro-inflammatory cyto- 189
124 two decades has seen a confusing array of reports on the levels kines in the serum, peripheral blood lymphocytes (PBL) mRNA or 190
125 of different cytokines with sometimes conflicting results. In equal resting and stimulated PBL between these groups. There was also 191
126 measure this is likely due to patient related variables and those no difference in serum levels of IL4, IFNc and soluble CD23 mea- 192
127 arising from methodological differences. The former include the sured by ELISA in 79 monozygotic (MZ) and 45 dizygotic (DZ) 193
128 precise patient selection criteria used, the different stages of the re- twins discordant for prolonged fatigue (Hickie et al., 1995). How- 194
129 lapse/remission cycle when patients were assessed, their precise ever, this work did suggest the importance of genetic factors in 195
130 levels of stress, physical activity and sleep disturbance and the encouraging fatigue. Thus persistent fatigue was more frequently 196
131 time of day that blood sampling occurred. Methodological issues concordant in the MZ versus the DZ twins. Additionally, this work 197
132 are particularly important in the reports on cytokine measure- also confirmed the major influence of a shared early environment 198
133 ments in those with CFS. Thus these can be studied by direct in affecting current immune function and unique environmental 199
134 immunoassay of serum/plasma, by immunoassay of in vitro cul- influences in encouraging fatigue. 200
135 ture supernatants of stimulated or unstimulated cultures of whole More recent work has looked at cytokine groups mediating dif- 201
136 blood or separated mononuclear cells, by gene expression in fering patterns of immune activity as quite often individual cyto- 202
137 mononuclear cells or by quantitative flow cytometry of intracellu- kine levels may not have differed significantly between patients 203
138 lar protein. Unfortunately the results obtained by one method are with CFS and age and sex matched healthy controls. Using a net- 204
139 difficult to compare to those obtained by another. work analysis Broderick et al. (2010) using the same data set used 205
140 Early reports looking particularly at the inflammatory cytokines earlier by Fletcher et al. (2009) assessed the co-expression of IL-1a, 206
141 showed a possible increase in several of these proteins. Indeed 1b, 2, 4, 5, 6, 8, 10, 12, 13, 15, 17 and 23, interferon (IFN) c, lympho- 207
142 (Moss et al., 1999) reported significantly elevated levels of tumour toxin-a (LT-a) and TNF-a in the plasma of 40 female CFS and 59 208
143 necrosis factor (TNF) a in patients with CFS compared to healthy case-matched controls. Cytokine co-expression networks were 209
144 controls. It is possible that such elevations may have accounted constructed from the pair-wise mutual information (MI) patterns 210
145 for the elevated levels of the inflammatory markers C-reactive pro- found within each subject group and showed diminution of T help- 211
146 tein (CRP), beta 2-microglobulin, and neopterin in the patients er (Th) 1 and Th17 function with an increase in Th2 type immunity. 212
147 with CFS reported by (Buchwald et al., 1997). However, patients There was also evidence of an attenuation of those networks that 213
148 with CFS also have significantly higher levels of bioactive trans- contribute to NK cell activation and IL12 and LT-a in particular. 214
149 forming growth factor (TGF) b compared to healthy controls, sub- While the evidence for significant alterations in the levels of the 215
Please cite this article in press as: Bansal, A.S., et al. Chronic fatigue syndrome, the immune system and viral infection. Brain Behav. Immun. (2011),
doi:10.1016/j.bbi.2011.06.016

3. YBRBI 1806 No. of Pages 8, Model 5G
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216 proinflammatory cytokines remains unclear the possibility that protein is induced by IFNa and IFNc and is an important defence 277
217 unchecked Th17 function with reduced suppression of the wild against viral proliferation leading to proposals that chronic viral 278
218 type IL17F allele by the His161Arg variant (C allele) has recently infection could be a possible cause of CFS. However, the detection 279
219 been presented by (Metzger et al., 2008). Thus the frequency of of several herpes viruses, enteroviruses and Borna viruses in 280
220 the C allele was significantly reduced in patients with CFS. patients with CFS by serology and PCR has provided conflicting re- 281
sults. Thus (Ablashi et al., 2000) found evidence of HHV-6 reactiva- 282
tion in their patients with CFS by detecting a raised frequency of 283
221 4. Cellular dysfunction
anti-HHV-6 IgM and the HHV-6 antigen in short term PBMC cul- 284
tures. In contrast, (Koelle et al., 2002) in a study of a cohort of 22 285
222 Although different patterns of raised circulating and stimulated
monozygotic twins in which one sibling from each twin was diag- 286
223 cytokines have been reported by different investigators, the only
nosed with CFS, suggested no serological evidence for a significant 287
224 abnormality consistently demonstrated by the majority of reports
difference in past or current infections with HHV-8, cytomegalovi- 288
225 on CFS is the reduction in the number (Masuda et al., 1994) or
rus, herpes simplex virus 1 and 2 or hepatitis C virus. Importantly 289
226 function (Barker et al., 1994) of NK cells. (Tirelli et al., 1994) also
the raw serological data such as antibody class or specificity were 290
227 found the reduced NK cell population to express an increased num-
not reported in this study. Additionally, the frequency of DNA 291
228 ber of adhesion (CD11b, CD11c and CD54) and activation (CD38)
detection by PCR for HHV-6, HHV-7, HHV-8, cytomegalovirus, Ep- 292
229 markers. (Klimas et al., 1990), however, found NK cells numbers
stein-Barr virus, herpes simplex virus, varicella zoster virus, JC 293
230 to be increased in subjects with CFS but for the NK cell cytotoxicity
virus, BK virus, and parvovirus B19 was not different between 294
231 to be reduced compared to healthy controls. (Levine et al., 1998)
the patients who fulfilled the criteria for CFS diagnosis and their 295
232 found NK cell function assessed in a 51Cr release assay to be lower
siblings who did not. However, the overall frequency of EBV detec- 296
233 in a family with CFS compared to family members without CFS.
tion in this study was considerably lower than the general popula- 297
234 Interestingly the latter in turn had 51Cr release results that were
tion (20% versus 80–90%) casting a doubt over the methodology. In 298
235 intermediate between those with CFS and healthy controls. (Stew-
an earlier study, (Buchwald et al., 1996) were also unable to find 299
236 art et al., 2003) have stressed the importance of ensuring compara-
serological evidence to support a role for viruses in 548 chronically 300
237 ble geographic controls in the comparison of subjects with and
fatigued patients. In their analysis they included herpes simplex 301
238 without CFS. (Ogawa et al., 1998) have shown the L-Arg-induced
virus 1 and 2, rubella, adenovirus, human herpesvirus 6, Epstein- 302
239 activation of NK activity by Nitrous Oxide to be impaired in CFS pa-
Barr virus, cytomegalovirus, and Cox-sackie B virus, types 1–6. In 303
240 tients. More recently (Brenu et al., 2010) have reported a decrease
contrast, (Manian, 1994) found serological evidence of an in- 304
241 in the CD56 (bright) CD16(À) population of NK cells with a signif-
creased frequency of previous EBV and Cox-sackie viruses B1 and 305
242 icantly reduced neutrophil oxidative burst both assessed flow cyto-
B4 in their investigation of 20 patients with CFS using standard 306
243 metrically in 10 patients with CFS. Thus several aspects of immune
well tested methodology. IgM antibodies to non structural genes 307
244 function appear to be affected in patients with CFS.
in human CMV have also been detected in a subset 16 out of 34 308
245 NK cell proliferation, maturation and activation are increased by
CFS patients with positive IgG against CMV envelope glycoproteins 309
246 several cytokines but particularly interleukin (IL) 21 and IFNc and
and in none of the 59 controls, 44 of whom were CMV IgG positive 310
247 especially in the presence of IL2, IL12, IL15 and IL18 (Strengell
(Lerner et al., 2002). This group also found IgM antibodies to EBV in 311
248 et al., 2002, 2003). NK cells recognize their targets by the absence
a subset of CFS patients suggesting that a defect in the immune 312
249 of classical HLA class I proteins and NK cell receptors of the KIR
system could be permitting reactivation of the virus (Lerner 313
250 superfamily. NK cell inhibitory receptors are also recognized and
et al., 2004). 314
251 important in regulating cytolytic activity.
The current literature is therefore mixed in relation to the sero- 315
252 CD69 is one of the earliest specific markers of NK cell activation
prevalence of the common viruses in CFS patients and this, at least 316
253 (Craston et al., 1997; Marzio et al., 1999; Llera et al., 2001). Acti-
to some degree, may be attributed to the different viral antigens 317
254 vated NK cells release cytokines that activate other NK cells and
used in different serological studies. Furthermore, the criteria used 318
255 the cellular immune system generally (Marzio et al., 1999). Ele-
in diagnosing CFS have been different in the early pre-2000 period 319
256 vated NK cell CD69 expression is associated with increased cyto-
compared to subsequent studies. In a study by (Kerr et al., 2000), 320
257 toxicity and target cell lysis (Lanier et al., 1988; De Maria et al.,
although no difference in seroprevalence for parvovirus B19 was 321
258 1994). The latter is achieved by NK cell release of perforin and
found, in contrast to healthy blood donor controls those fulfilling 322
259 granzymes that induce target cell apoptosis and cell membrane
the Fukada criteria for CFS had significantly raised frequency of 323
260 destruction. As NK cells are important in the elimination of virally
IgG antibodies to the parvovirus B19 NS1 protein (41.5% versus 324
261 infected/altered host cells it is possible that impaired NK cell func-
7%). Additionally, viral DNA detected by real time PCR was evident 325
262 tion may allow the persistence of chronic viral infection in subjects
in 11 out of the 200 CFS patients and in none of the 200 healthy 326
263 with CFS. Interestingly, (Maes et al., 2005) found reduced levels of
controls. The results were suggested to indicate deficient control 327
264 CD69 T cells and (Mihaylova et al., 2007) reduced levels of CD69 T
of parvovirus B19 perhaps in relation to impaired cellular immu- 328
265 and NK cells in patients with CFS. It is therefore possible that CFS
nity. On the other hand detection of antibodies with unusual spec- 329
266 may be associated with the impaired T and NK cell activation as re-
ificities may suggest an altered immune response to viruses or 330
267 duced secretion of those cytokine important in regulating NK cell
altered viral replication in patients diagnosed with CFS. Further 331
268 function. This in turn may be caused by specific polymorphisms
dysregulation of viral immunity is also suggested by the finding 332
269 in the promoter regions of IL21, IFNc, IL2, IL12, IL15 and IL18. How-
of antibodies to mitochondrial components and also to serotonin, 333
270 ever, NK cell activity has been shown to be adversely affected by
microtubule-associated protein 2 and muscarinic cholinergic 334
271 depression and sleep (Irwin et al., 1992).
receptor 1 (Bassi et al., 2008). 335
Fatigue is a known consequence of several viral infections and 336
272 5. CFS and viral infection in the case of EBV this has been reported to last a median of eight 337
weeks and with an interquartile range of four to sixteen weeks 338
273 Several investigators have reported increased 20 50 oligoadeny- (White et al., 1998). Stress has also been reported to reactivate 339
274 late synthetase (OAS) activity by mononuclear cells of patients EBV (Glaser et al., 2005) and it is possible that the increased stress 340
275 with CFS and the levels correlating with disease severity (Vojdani suffered by patients with CFS may contribute to recurrent relapses 341
276 and Lapp, 1999; Ikuta et al., 2003; Nijs and Fremont, 2008). This in CFS. With this is in mind it is interesting that valacyclovir has 342
Please cite this article in press as: Bansal, A.S., et al. Chronic fatigue syndrome, the immune system and viral infection. Brain Behav. Immun. (2011),
doi:10.1016/j.bbi.2011.06.016

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343 been shown beneficial in subset of patients with CFS with previous was thus called xenotropic MLV-related virus (XMRV). Although 387
344 EBV infection and particularly in regard to cardiac function (Lerner there is no evidence to suggest an increase in prostate cancer 388
345 et al., 2007). Mechanistically purified EBV deoxyuridine triphos- among CFS patients, the link with RNase L function led a team from 389
346 phate nucleotidohydrolase (dUTPase) has been shown to inhibit the Whittemore Peterson Institute to look for the virus in their CFS 390
347 the replication of human PBMCs in vitro and to increase the pro- cohort. In late 2009, they reported that they had found XMRV nu- 391
348 duction of several cytokines (Glaser et al., 2005). These included cleic acid in white blood cells from 68/101 CFS patients compared 392
349 TNFa, IL1b, IL6, IL8, and the immune regulatory IL10. Additionally, to only 8/218 controls (Lombardi et al., 2009), although they did 393
350 it increased NK cell lysis of target cells. In mice this group also not find a link to RNase L deficiency. The extremely high preva- 394
351 found EBV dUTPase to significantly inhibit the replication of mito- lence of the virus in CFS patients caused great excitement, espe- 395
352 gen-stimulated lymphocytes and the synthesis of IFNc by lymph cially as the authors claimed to have cultured virus from these 396
353 node and splenic cells (Glaser et al., 2005). Inoculation was associ- patient samples. However, the story was soon mired in confusion 397
354 ated with an increase in body temperature, decrease in body mass as three groups quickly published contrary reports that they could 398
355 and physical activity known to be induced by pro-inflammatory find little evidence of the virus in their patient cohorts (Erlwein 399
356 cytokine secretion. Subsequently this same group has shown that et al., 2010; Groom et al., 2010; van Kuppeveld et al., 2010). Two 400
357 depletion of CD14+ monocytes attenuated cytokine secretion (Gla- of the reports were criticised for only using PCR based assays, how- 401
358 ser et al., 2006). Furthermore, the pathway of proinflammatory ever the third also used serological tests (Groom et al., 2010). Addi- 402
359 cytokine secretion by EBV dUTPase involved the initial binding of tional negative reports soon followed, and, to date, no other group 403
360 Toll like receptor 2 and subsequent activation of NF-kappaB has published similar findings of XMRV in CFS patients. The story 404
361 through the recruitment of the MyD88 adaptor molecule (Ariza has been complicated further by reports of other MLV-like viruses 405
362 et al., 2009). Of relevance to patients with CFS, glucocorticoids that in CFS patients (Lo et al., 2010) and sample contamination (Smith, 406
363 are secreted as part of the stress response have been shown to in- 2010). Despite a high profile, the association between XMRV and 407
364 duce lytic replication of latent EBV through the induction of the CFS is still very uncertain and requires further investigation. How- 408
365 immediate early gene BZLF1 (Yang et al., 2010). Importantly, how- ever, there is increasing evidence that this has little to do with CFS 409
366 ever, dexamethasone also induced the early BLLF3 gene that en- and current evidence is far more in favour of one or more herpes 410
367 codes EBV dUTPase as well as BALF5 that encodes the EBV DNA viruses and/or possibly an enterovirus being involved. 411
368 polymerase. Thus stress induced EBV reactivation may represent
369 the initial problem that leads to a disturbance of immune memory
370 which in turn leads to a prolongation and accentuation of viral 6. CFS, immunodeficiency and disturbed immunological 412
371 symptoms. memory 413
372 Regarding other viruses, (Lane et al., 2003) have reported
373 enterovirus sequences in the quadriceps of their patients with con- We have recently observed the frequency of fatigue and other 414
374 firmed CFS and evidence of muscle weakness. (Chia et al., 2010) de- symptoms compatible with CFS, diagnosed on the basis of the 415
375 tected enteroviral RNA in peripheral blood of two and gastric antral Canadian and Fukada criteria, to be increased at least twenty fold 416
376 biopsy of one patient after an acute illness that had progressed to in patients with primary antibody deficiency (unpublished). Addi- 417
377 chronic fatigue. These findings support previous work suggesting a tionally, we have also observed impaired specific antibody produc- 418
378 persistence of enteroviral infection in patients with CFS (Galbraith tion in a number of patients with CFS whose serum antibody levels 419
379 et al., 1997). In addition to viruses several other organisms have are otherwise within normal levels. These patients had recurrent 420
380 also been considered to be associated with chronic fatigue. These sore throats accompanied by bronchitis but not pneumonia or 421
381 include several types of bacteria including mycoplasma species invasive disease. Together these findings suggest that immune dys- 422
382 in particular (Vojdani et al., 1998) but also borrelia. function predisposes to CFS type symptoms and that at least some 423
383 In 2006, researchers investigating a link between the OAS path- patients with CFS have a defect of immune memory. Indeed our 424
384 way and familial prostate cancer identified a novel retrovirus in early work confirms a defect of both B and T cell memory in pa- 425
385 samples from patients with a deficiency in RNase L function. This tients fulfilling the Fukada and Canadian criteria for CFS. Fig. 1 in 426
386 virus was similar to known murine leukaemia viruses (MLV) and a simplified way summarises the interaction between viral 427
Cellular Immune Reactivation of pre-
dysfunction/exhaustion, existing chronic
Severe/prolonge impaired T and B cell viral infection or
d viral and/or memory and altered NK new viral infections
cell activity
other infections
FATIGUE
Viral proteins induced
Stress associated with pro-inflammatory
anxiety, depression, cytokine release with
insomnia, inactivity elevated parameters of
inflammation
Fig. 1. The inter-relationship between psychosocial, immune and viral factors in the initiation and perpetuation of chronic fatigue.
Please cite this article in press as: Bansal, A.S., et al. Chronic fatigue syndrome, the immune system and viral infection. Brain Behav. Immun. (2011),
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428 infections, stress/sleep disturbance and impaired immune memory costimulatory function. Interestingly recent work shows reduced 494
429 function. CD8 T cell and NK cell cytotoxicity in 95 patients with CFS com- 495
430 Normally, B cell memory appears to be maintained by a combi- pared to 50 healthy controls (Brenu et al., 2011). Our own work 496
431 nation of long lived memory cells and constant antigen stimulation has also shown significantly reduced activated CD8+ CD27+ 497
432 of B cells within lymph nodes by antigen retained by follicular den- CD28+ cytotoxic T memory cells in 14 patients with CFS as well 498
433 dritic cells. In patients with established immunodeficiency recent as a trend to reduced IL15Ra expression after mitogen activation 499
434 work has confirmed reductions in the various memory B cell pop- (unpublished). 500
435 ulations in those with common variable immunodeficiency (CVID). There is now good evidence that EBV can cause major altera- 501
436 Interestingly, reduced numbers of switched memory B cells (CD19, tions in T cell memory function. Thus in acute EBV induced mono- 502
437 CD27+ IgDÀ) have been found in CVID patients with splenomegaly nucleosis, the expression of IL-7Ra was lost by all CD8+ T cells, 503
438 and a tendency to granulomatous organ infiltration (Mouillot et al., including EBV epitope-specific populations (Sauce et al., 2006). 504
439 2010). In those patients with autoimmune manifestations the While expression was rapidly regained on total CD8+ cells it was 505
440 number of unswitched memory B cells is increased. In patients only slowly and incompletely regained on EBV-specific memory 506
441 with CFS a reduction in the numbers of CD19/IgM+ B cells has been cells. In contrast, although the expression of IL-15a was also lost 507
442 observed (Lundell et al., 2006) although the exact significance of in acute EBV mononucleosis it remained undetectable not just on 508
443 this is unclear as CFS has never been linked to a deficiency of anti- EBV-specific CD8+ populations but on the whole peripheral T- 509
444 body immunity or recurrent bacterial infections. However, in a re- and natural killer (NK)-cell pool. Of importance this defect in 510
445 cent paper, a monoclonal antibody that depletes B cells was found IL15Ra expression and defective IL-15 responsiveness in vitro, 511
446 to markedly improve the clinical symptoms in three patients with was consistently observed in patients up to 14 years after infec- 512
447 CFS (Fluge and Mella, 2009) suggesting that B cells have a role in tious mononucleosis (IM). However, it was absent in patients after 513
448 the pathogenesis of CFS. Whether B cells harbouring EBV were re- cytomegalovirus (CMV)-associated mononucleosis, in healthy EBV 514
449 moved by this process was not formally assessed but clearly likely. carriers with no history of IM and in EBV-naive individuals. It is 515
450 T cell memory appears to be more complex and is based partly possible that a similar situation is likely evident in at least a pro- 516
451 on the strength of the initial Tcell receptor – antigen MHC interac- portion of patients with CFS of acute onset and following a viral ill- 517
452 tion (Kim and Williams, 2010). While acute viral infections often ness. Thus EBV may be responsible for not only causing a defect in 518
453 stimulate marked expansion of the naïve T cell pool, chronic viral its own control but may be also a reduction in immune activity to 519
454 infections with continued immune stimulation may lead to im- other infectious agents. Interestingly, EBV infection can be associ- 520
455 mune exhaustion particularly of the CD8 T cells (Angelosanto ated with the production of a variety of auto-antibodies of varying 521
456 and Wherry, 2010). The extent of clonal expansion is important avidity and clinical significance. It is presently unclear whether 522
457 and CD8 T cell memory requires a combination of IL15 and to a les- anti-cytokine antibodies are present in patients with CFS as has 523
458 ser degree IL7 while CD4 memory requires both T cell receptor been uncovered in several seemingly unrelated conditions. These 524
459 stimulation and IL7. Downstream to this, the balance of pro-apop- include chronic mucocutaneous candidiasis (IL17), pulmonary 525
460 totic factors such as TNFR-6 (Fas) and Bcl2-like protein 11 (BIM) alveolar proteinosis (GM-CSF), certain types of disseminated non- 526
461 and anti-apoptotic factors Bcl2 determine the fate of T cells (Bever- tuberculous mycobacterosis (IFNc) and some people with severe 527
462 ley, 2008). Survival genes such as Tbet and eomesodermin gain staphylococcal skin infection (IL6) (Browne and Holland, 2010). 528
463 importance because of their ability to maintain expression of the
464 IL15a receptor (CD122). This appears to be particularly important
465 in CD8 T cell memory while the HIV type I enhancer protein 2 (HI- 7. Treatment options for CFS by immune modulation and anti- 529
466 VEP2 or Schnurri-2) appears more important for CD4 T cells. For all viral therapy 530
467 T cells long lived memory is maintained most significantly by con-
468 tinued antigen stimulation or cross reactive antigen stimulation. It is clear that current treatment strategies have only a limited 531
469 This is certainly evident in persistent viral infections such as those ability to ‘cure’ CFS and restore premorbid physical and mental sta- 532
470 caused by EBV and HIV. mina. Routine anti-inflammatory agents while helpful in a small 533
471 During an initial immune response CD8 T cells appear to show proportion of individuals do little to arrest continued viral prolifer- 534
472 massive expansion and then contraction with subsequent long ation and restore immune memory function that prevents further 535
473 lived stable memory populations. These phases are much less in- viral infections. This is also true of glucocorticoid steroids that 536
474 tense in CD4 T cells which also show very slow loss of memory can reduce the synthesis of pro-inflammatory cytokines but are 537
475 cells (Beverley, 2008). unable to stimulate anti-viral cellular immunity and immune 538
476 Recent work has also confirmed the importance of IL15 in the memory. Indeed they often worsen anti-viral immunity. Intrave- 539
477 generation and maintenance of CD8/CD44hi memory T cells. Thus, nous immunoglobulin therapy likewise does not address the areas 540
478 transfer experiments have shown IL15 dependent dendritic cells of immune dysfunction and like steroids reduce further NK cell 541
479 (DC) in optimising the survival and proliferation of NK cells and activity (Thum et al., 2008). Unsurprisingly it provided no benefit 542
480 CD8/CD44hi memory T cells (Koka et al., 2004; Burkett et al., in 99 patients with CFS treated with three different doses of IVIg 543
481 2004). IL15 and its receptor were induced by IFNc and NFjB relA at monthly intervals for 3 months in a double blind placebo con- 544
482 inducers and conferred an autocrine loop resistance to apoptosis trolled trial (Vollmer-Conan et al., 1997). Regarding interferon 545
483 that accompanied DC maturation (Dubois et al., 2005). More recent therapy this is able to stimulate cellular immune function. In seven 546
484 work has shown stable complexes of IL15 with its receptor on cell CFS patients with initially impaired NK cell function treated with 547
485 surfaces. The IL15a receptor here presented IL15 in trans configu- 12 weeks interferon a 2a therapy a significantly improved quality 548
486 ration that allowed stimulation of neighbouring T and NK cells of life was evident (See and Tilles, 1996). It was unclear why there 549
487 (Burkett, Koka et al., 2004; Sato et al., 2007). While these com- was no improvement in patients with impaired lymphocyte prolif- 550
488 plexes underwent endosomal internalisation they appeared to be eration or CFS patients generally. Also inexplicable is why NK cell 551
489 resistant to lysosomal degradation and were re-circulated to the function was impaired in these patients when other investigators 552
490 cell surface as a reservoir of IL15 that maintained memory function have reported increased levels of interferon inducible proteins in 553
491 by CD8/CD44hi memory T cells (Sato et al., 2007). Such complexes patients with viral and chemical induced CFS (Vojdani and Lapp, 554
492 would explain the absence of any significant circulating levels of 1999). Nonetheless, further work is required to see if interferon 555
493 IL15 and the need for cell to cell proximity in ensuring strong therapy may help that subset of CFS patients with demonstrably 556
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557 impaired cellular immunity. Clearly the possibility of inducing new suggests mildly raised circulating pro-inflammatory cytokines 620
558 autoimmunity particularly to thyroid tissue would need to be bal- and a skewing towards impaired cellular immunity. More work is 621
559 anced against any benefit. needed to take into account the level of stress and sleep distur- 622
560 Based on impaired immune memory function in patients with bance amongst the study population and to correlate the immune 623
561 CFS, and particularly affecting the CD8 T cell population which is function with the patient’s perception of how severe their symp- 624
562 especially important in controlling EBV infected B cells, four meth- toms were at the time of immune analysis. Most importantly of 625
563 ods of treatment may prove beneficial. The first would involve all more longitudinal studies investigating immune function with 626
564 restoring CD8 T cell memory function using complexes of IL15Ra changes in the severity of CFS symptoms are urgently needed. It 627
565 and IL15. In mice this has markedly increased IL-15 half-life and is likely that viral infection(s) and immune dysfunction in CFS 628
566 bioavailability leading to a significant proliferation of memory interact in a manner which perpetuates the conditions necessary 629
567 CD8 T cells, NK cells, and NK T cells (Stoklasek et al., 2006). As for maintaining symptoms. Fig. 1 summarises the interplay be- 630
568 yet there are no studies of IL15 on memory T cells in CFS. tween the important variables. It is likely that an initial viral infec- 631
569 The second method would involve using agents active against tion or stress acting singly or in combination leads to a state of 632
570 EBV. In this case the use of valacycolvir has been shown in a double impaired cellular immunity, immune memory dysfunction and dis- 633
571 blind placebo controlled trial lasting 36 months to improve cardiac turbed NK cell activity. This promotes reactivation of previously 634
572 dysfunction and resume normal life in patients with confirmed CFS acquired EBV or related virus infection and wide dissemination 635
573 (Lerner et al., 2007). Additionally, valgancyclovir, in an open la- of the original viral infection. EBV and other viral proteins stimu- 636
574 beled study, has also been shown to be extremely beneficial in late the release of pro-inflammatory cytokines which contribute 637
575 12 patients with symptoms highly suggestive of CFS and who to fatigue, low grade fever, aching, disturbance of sleep and inac- 638
576 had high titre antibodies to HHV6 and EBV (Kogelnik et al., tivity. The severity and prolonged nature of these symptoms 639
577 2006). The results of the randomized double blind study while encourages further stress leading to continued immune paresis 640
578 not formally published appeared not to have shown significant and production of immune dysregulating viral proteins. The latter 641
579 benefit suggesting that continued EBV/viral suppression requires then perpetuate the immune dysfunction with continuation of 642
580 at least partial restoration of global T cell memory to be effective. symptoms. In view of the significant interaction between each of 643
581 Lastly, and most recently, (Lerner et al., 2010) in a retrospective these areas, treatments targeting several areas simultaneously 644
582 analysis have reported significant benefit of unblinded valacyclovir are more likely to be successful than those used selectively in 645
583 or valgancyclovir in 142 patients with CFS treated between 2001 one area. 646
584 and 2007 who had active EBV, CMV or HHV6 infection. Improve-
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Please cite this article in press as: Bansal, A.S., et al. Chronic fatigue syndrome, the immune system and viral infection. Brain Behav. Immun. (2011),
doi:10.1016/j.bbi.2011.06.016