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Possible pathogenic nature of the recently discovered TT virus: Does it play a role in autoimmune rheumatic diseases?
Autoimmunity Reviews 6 (2006) 5 – 9 www.elsevier.com/locate/autrev
Possible pathogenic nature of the recently discovered TT virus: Does it play a role in autoimmune rheumatic diseases? Peter Gergely Jr. a,b , Andras Perl c , Gyula Poór a,b,⁎ a National Institute of Rheumatology and Physiotherapy, Frankel Leó u. 38-40, H-1023 Budapest, Hungary Musculoskeletal Molecular Biology Research Group, Hungarian Academy of Sciences, Frankel Leó u. 38-40, H-1023 Budapest, Hungary Departments of Medicine, Microbiology and Immunology, State University of New York, Upstate Medical University, College of Medicine, 750 East Adams Street, Syracuse, NY 13210, USA b
c
Available online 19 April 2006
Abstract Pathogenesis of viral origin has long been suggested in autoimmune rheumatic diseases. Beside the well-defined virus induced transient or chronic rheumatic diseases often resembling systemic autoimmune disorders such as rheumatoid arthritis, viruses can contribute to disease pathogenesis by several different pathomechanisms. TT virus is a recently discovered virus of extremely high genetic diversity which commonly infects humans. Despite accumulated evidence on the biological characteristics of TTV, its pathogenicity is still in question; many consider TTV as a harmless endosymbiont. The recent paper overviews the biology of TT virus and investigates the hypothesis that TTV might have a causative role in human diseases with special attention to the possibility that TTV might trigger autoimmunity in rheumatic disorders. © 2006 Elsevier B.V. All rights reserved. Keywords: TT virus; Pathogenesis; Autoimmunity; Rheumatic disorders
Contents 1. Introduction . . . . . . . . . . . . . . . . . 2. Biological characteristics of TTV . . . . . . 3. Possible pathogenicity of TTV . . . . . . . . 4. TT virus in autoimmune rheumatic disorders: 5. Conclusion . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . Take-home messages . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . .
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⁎ Corresponding author. 1st Department of Rheumatology and Metabolic Osteology, National Institute of Rheumatology and Physiotherapy, Frankel Leó u. 38-40, H-1023 Budapest, Hungary. Tel.: +36 1 438 8300; fax: +361 355 2779. E-mail address: [email protected] (G. Poór). 1568-9972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.autrev.2006.03.002
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1. Introduction Autoimmune rheumatic diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), idiopathic
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P. Gergely Jr. et al. / Autoimmunity Reviews 6 (2006) 5–9
inflammatory myopathies (IIM) or systemic sclerosis (SSc) are of unknown etiology. They constitute a heterogeneous group of chronic multisystem inflammatory disorders characterised by involvement of musculoskeletal structures and variably associated with extraarticular manifestations. Several lines of independent evidence indicate that a trigger, possibly a virus operating on the background of strong genetic and hormonal predisposing factors may be involved in their etiopathogenesis. Beside direct pathogenicity in virus-induced arthralgy/arthritis syndromes, a number of different pathomechanisms have been suggested in autoimmune rheumatic diseases. These include molecular mimicry between viral proteins and autoantigens, T or B cell dysfunctions as a result of an inadequate response to the pathogen in the genetically susceptible host or other immunregulatory abnormalities caused by viral proteins [1]. TT virus is a newly identified DNA virus of unknown pathogenicity which commonly infects humans [2]. Although a vast amount of data has been accumulated on its biological characteristics since its discovery in 1997 [3], very few evidences are available regarding the prevalence or possible role of the virus in autoimmune disorders. 2. Biological characteristics of TTV Nishizawa et al. identified TTV by representational difference display analysis in the serum of a Japanese patient with acute post-transfusion hepatitis of unknown etiology in 1997 [4]. The virus was first named after the initials of the patient then was renamed transfusion–transmitted virus. The small DNA virus with a unique unenveloped single-stranded circular DNA genome of negative polarity had originally been classified into the Circoviridae family [5]. Phylogenetic analysis of TTV isolates sourced from different parts of the world demonstrates an extremely high genetic diversity [6]. Due to this fact and difficulties in expression of full-length TTV protein in prokaryotic or eukaryotic cells, and generation of pan-specific TTV antibodies, diagnosis of TTV infection has been dependent on PCR detection of viral DNA using primers specific for the conservative non-coding regions [7]. TTV has earlier been documented in various types of human samples including serum, peripheral blood mononuclear cells, stool, saliva, bile, breast milk or synovial fluid [8,9]. Infection with TTV appears ubiquitous across different human populations, several primate species and in farm animals [10]. Various genotypes of the virus have been detected with frequencies ranging from 2% to 90% in serum of healthy blood donors [11,12]. To date, a culture system capable of supporting adequate replication of TTV has not been available, nor has
the virus been visualized with certainty by electron microscopy. However, TTV has been transmitted to chimpanzees and rhesus monkeys by intravenous inoculation of virus-positive human sera or fecal extracts [13]. Transfection of competent TTV DNA induces mRNA transcription, but not DNA replication, in cultured cells [14]. Despite the increasing amount of data, many aspects of the biology of TTV, i.e. method of replication, antibody production against TTV-derived proteins, significance of its global presence and high genomic variability, cell tropism, replicational and transcriptional regulation have not yet been elucidated. 3. Possible pathogenicity of TTV Since the first isolation of TTV, most studies have focused on its possible role in liver disorders and reported a possible association in fulminant hepatitis, cryptogenic liver disease, non A–G or post transfusion hepatitis, liver cirrhosis and hepatocellular carcinoma [2–4,7]. Higher mortality has also been reported among acute hepatitis patients co-infected with TTV and hepatitis B [3]. The association between liver diseases and TTV, however, seems conflicting. There is a bulk of evidence reporting the absence of such associations. Furthermore, morphological changes within TTV-infected hepatocytes could not be detected [15]. Clinical course and laboratory parameters of patients with hepatitis co-infected with TTV were not different from those without TTV co-infection [16]. Epidemiological associations of TTV with B cell lymphoma and Hodgkin's disease [17], aplastic anemia [18], idiopathic pulmonary fibrosis [19], acute respiratory disease [20] have also been described. TTV infection was also associated with poor clinical outcome in laryngeal cancer in a recent Hungarian study [21] and high TTV viremia was reported to result in decreased survival in HIV positive patients [22]. Although some studies found differences in the biological or possibly pathogenic properties of different genogroups of TTV [21], the significance of the genetic variants is unknown at present. Almost all evidences supporting a role for TTV in human diseases consist of epidemiological surveys; and it has still not been determined whether TTV is capable of causing any human disease. 4. TT virus in autoimmune rheumatic disorders: casual coincidence or causative agent? A few independent studies have provided no compelling evidence that TTV has a pathogenic role in autoimmune hepatitis. In the first study to assess TTV infection rate in rheumatic diseases, a diminished TTV prevalence
P. Gergely Jr. et al. / Autoimmunity Reviews 6 (2006) 5–9
was found in patients with RA in comparison to controls of unselected pathology and in patients with SLE [23]. Seemayer et al. found similar percentage of TTV DNA positivity in serum samples of patients with RA and SSc which was comparable to that of patients with osteoarthritis (OA) and normal blood donors [24]. We were able to identify TT virus DNA in the synovial fluid of patients with RA and OA using a sensitive real-time PCR and melting curve analysis but found the detection rate similar [9]. Recently, a TTV-derived putative protein was shown to induce apoptosis in various human hepatocellular carcinoma cell lines [25]. Although dysregulated apoptosis has been known to play a crucial role in several autoimmune diseases such as SLE, the significance of this finding is to be further confirmed and clarified. We identified novel immunodominant epitopes of the 28 kDa HTLV I-related retroviral element (HRES-1/ p28) autoantigen and investigated their cross-reactivity with antigens of infectious viruses [26]. HRES-1 is an endogenous retroviral element encoding a 28-kDa nuclear autoantigen, HRES-1/p28, which is expressed in a tissue-specific manner [27]. Antibodies to HRES-1/ p28 were detected in 21–50% of patients with SLE and overlap syndromes in various laboratories in contrast to normal donors or HIV-infected patients [28]. Two of the identified immunodominant epitopes showed significant sequence homology to different open reading frames of TTV. In our experiment, all HRES-1/p28-reactive sera recognized at least one TTV-specific peptide. Further, a putative TTV capsid peptide having no homology to HRES-1/p28, was also recognized by the majority of lupus sera. Most prominent reactivity with TTV-derived peptides was associated with the presence of TTV DNA in patients with SLE. We found prevalence of TTV DNA significantly elevated in SLE patients (120/211) with respect to healthy control donors (66/199) or patients with RA (23/91). Interestingly, first-degree healthy relatives of lupus patients (51.3%) had a significantly lower TTV infection rate than lupus patients (66.1%) but a higher infection rate than healthy donors from families without lupus (33.9%). Thus, genetic factors underlying susceptibility to SLE may also influence infection by TTV. In addition to HRES-1/p28 epitopes showing similarity to TTV proteins, lupus sera had strong binding affinity to a peptide showing similarity to the retroviral gag-like region of 70 k U1 snRNP lupus autoantigen suggesting that cross-reactivity of HRES-1/p28 with TTV and 70 k U1 snRNP may lead to epitope spreading and contribute to generation of anti-nuclear antibodies. In a separate study we detected TTV DNA in 61/94 (64.9%) patients with IIM which did not differ
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Table 1 Arguments for and against the hypothesized pathogenic role of TTV in autoimmune rheumatic disorders For
Against
▪ Increased prevalence in SLE vs healthy controls or RA patients ▪ Epidemiological association with severe IIM ▪ Humoral response to TTV specific peptides in SLE ▪ Sequence homology and possible molecular mimicry between immunodominant epitopes of HRES-1 and TTV specific peptides in SLE ▪ Possibility of epitope spreading and generation of anti-nuclear antibodies due to crossreactivity of HRES-1/p28 with TTV and 70 k U1 snRNP ▪ Capability of a TTV-derived putative protein of inducing apoptosis
▪ Global presence in normal population ▪ Inconclusive and conflicting data of epidemiological associations in several diseases ▪ Paucity of data on humoral response against TTV derived proteins ▪ Unknown cause and significance of the extremely high genomic variability ▪ Undetermined differences in biological properties of certain TTV genogroups ▪ Lack of morphological or molecular abnormalities of TTV infected cells ▪ Paucity of data on autoimmune rheumatic diseases ▪ Lack of conclusive data supporting the pathogenic nature of TTV in general
significantly from patients with RA and from healthy individuals [29]. However, patients with more severe IIM had a significantly higher rate of TTV infection indicating that TTV infection might be a prognostic factor in IIM. 5. Conclusion Despite intensive efforts to clarify the pathogenic nature of TTV, the virus could not be causally associated with any disease and many researchers consider TTV an orphan or harmless virus, or even a symbiont. Its causal role in autoimmune rheumatic diseases can be hypothesized based on only a few studies including two of our own. Our data support the notion that molecular mimicry of immunodominant ERV epitopes may confer cross-reactivity with TTV antigens, mediate epitope spreading to self antigens such as the 70 kDa U1 snRNP, and thus contribute to formation of antinuclear autoantibodies in SLE. TTV infection may also be associated with a more severe clinical outcome in patients with IIM. Although arguments against its causative role in human diseases, especially in rheumatic disorders far outweigh the proofs for it (Table 1), pathogenicity of TTV cannot be ruled out. It will be interesting to
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discover whether TTV infected individuals are, indeed, innocent bystanders or there will be ultimate consequences of carrying the virus. This issue is certainly worth further research. Acknowledgement This work was supported by the Hungarian Scientific Research Fund OTKA T042637 and by grants RO1 AI 48079 and FO5 TW05421 from the National Institutes of Health, USA. Take-home messages • Viral etiology has long been suggested in autoimmune rheumatic disorders. • TT virus, a recently discovered virus with extremely high genetic diversity commonly infects humans. • Despite accumulated evidence on the biology of TTV its pathogenicity is unknown. • There are very few evidences supporting its role in autoimmune rheumatic disorders; these include an increased prevalence in SLE and in severe IIM and a possible molecular mimicry between TTV and HRES-1/p28, an endogenous retroviral protein. • At present, TTV is mostly considered as a harmless virus. References [1] Perl A. Mechanisms of viral pathogenesis in rheumatic disease. Ann Rheum Dis 1999;58:454–61. [2] Okamoto H, Nishizawa T, Ukita M. A novel unenveloped DNA virus (TT virus) associated with acute and chronic non-A to G hepatitis. Intervirology 1999;42:196–204. [3] Abraham P. TT viruses: how much do we know? Indian J Med Res 2005;122:7–10. [4] Nishizawa T, Okamoto H, Konishi K, Yoshizawa H, Miyakawa Y, Mayumi M. A novel DNA virus (TTV) associated with elevated transaminase levels in posttransfusion hepatitis of unknown etiology. Biochem Biophys Res Commun 1997;241:92–7. [5] Mushahwar IK, Erker JC, Muerhoff AS, Leary TP, Simons JN, Birkenmeyer LG, et al. Molecular and biophysical characterization of TT virus: evidence for a new virus family infecting humans. Proc Natl Acad Sci U S A 1999;96:3177–82. [6] Bendinelli M, Pistello M, Maggi F, Fornai C, Freer G, Vatteroni ML. Molecular properties, biology, and clinical implications of TT virus, a recently identified widespread infectious agent of humans. Clin Microbiol Rev 2001;14:98–113. [7] Biagini P, Gallian P, Attoui H, Cantaloube JF, Touinssi M, de Micco P, et al. Comparison of systems performance for TT virus detection using PCR primer sets located in non-coding and coding regions of the viral genome. J Clin Virol 2001;22:91–9. [8] Ross RS, Viazov S, Runde V, Schaefer UW, Roggendorf M. Detection of TT virus DNA in specimens other than blood. J Clin Virol 1999;13:181–4.
[9] Gergely P, Blazsek A, Weiszhar Z, Poor G. Relationship between TT virus infection and autoimmune rheumatic diseases. Ann Rheum Dis 2004;63(S1):65–65 (abstract). [10] Leary TP, Erker JC, Chalmers ML, Desai SM, Mushahwar IK. Improved detection systems for TT virus reveal high prevalence in humans, non-human primates and farm animals. J Gen Virol 1999;80:2115–20. [11] Biagini P. Human circoviruses. Vet Microbiol 2004;98:95–101. [12] Huang LY, Oystein Jonassen T, Grinde B, et al. High prevalence of TT virus-related DNA (90%) and diverse viral genotypes in Norwegian blood donors. J Med Virol 2001;64:381–6. [13] Okamoto H, Fukuda M, Tawara A, Nishizawa T, Itoh Y, Hayasaka I, et al. Species-specific TT viruses and cross-species infection in nonhuman primates. J Virol 2000;74:1132–9. [14] Desai MM, Pal RB, Banker DD. Molecular epidemiology and clinical implications of TT virus (TTV) infection in Indian subjects. J Clin Gastroenterol 2005;39:422–9. [15] Rodriguez-Inigo E, Casqueiro M, Bartolome J, Ortiz-Movilla N, Lopez-Alcorocho JM, Herrero M, et al. Detection of TT virus DNA in liver biopsies by in situ hybridization. Am J Pathol 2000;156:1227–34. [16] Watanabe H, Shinzawa H, Shao L, Saito T, Takahashi T. Relationship of TT virus infection with prevalence of hepatitis C virus infection and elevated alanine aminotransferase levels. J Med Virol 1999;58:235–8. [17] Garbuglia AR, Iezzi T, Capobianchi MR, Pignoloni P, Pulsoni A, Sourdis J, et al. Detection of TT virus in lymph node biopsies of B-cell lymphoma and Hodgkin's disease, and its association with EBV infection. Int J Immunopathol Pharmacol 2003;16:109–18. [18] Miyamoto M, Takahashi H, Sakata I, Adachi Y. Hepatitisassociated aplastic anemia and transfusion-transmitted virus infection. Intern Med 2000;39:1068–70. [19] Bando M, Ohno S, Oshikawa K, Takahashi M, Okamoto H, Sugiyama Y. Infection of TT virus in patients with idiopathic pulmonary fibrosis. Respir Med 2001;95:935–42. [20] Maggi F, Pifferi M, Fornai C, Andreoli E, Tempestini E, Vatteroni M, et al. TT virus in the nasal secretions of children with acute respiratory diseases: relations to viremia and disease severity. J Virol 2003;77:2418–25. [21] Szladek G, Juhasz A, Kardos G, Szoke K, Major T, Sziklai I, et al. High co-prevalence of genogroup 1 TT virus and human papillomavirus is associated with poor clinical outcome of laryngeal carcinoma. J Clin Pathol 2005;58:402–5. [22] Christensen JK, Eugen-Olsen J, SLrensen M, Ullum H, Gjedde SB, Pedersen BK, et al. Prevalence and prognostic significance of infection with TT virus in patients infected with human immunodeficiency virus. J Infect Dis 2000;181:1796–9. [23] Maggi F, Fornai C, Morrica A, Casula F, Vatteroni ML, Marchi S, et al. High prevalence of TT virus viremia in italian patients, regardless of age, clinical diagnosis, and previous interferon treatment. J Infect Dis 1999;180:838–42. [24] Seemayer CA, Viazov S, Gay S, et al. Prevalence of TTV DNA and GBV-C RNA in patients with systemic sclerosis, rheumatoid arthritis, and osteoarthritis does not differ from that in healthy blood donors. Ann Rheum Dis 2001;60:806–9. [25] Kooistra K, Zhang YH, Henriquez NV, Weiss B, Mumberg D, Noteborn MH. TT virus-derived apoptosis-inducing protein induces apoptosis preferentially in hepatocellular carcinomaderived cells. J Gen Virol 2004;85:1445–50. [26] Gergely Jr P, Pullmann R, Stancato C, Otvos Jr L, Koncz A, Blazsek A, et al. Increased prevalence of transfusion–transmitted virus and cross-reactivity with immunodominant epitopes of the
P. Gergely Jr. et al. / Autoimmunity Reviews 6 (2006) 5–9 HRES-1/p28 endogenous retroviral autoantigen in patients with systemic lupus erythematosus. Clin Immunol 2005;116:124–34. [27] Banki K, Maceda J, Hurley E, Ablonczy E, Mattson DH, Szegedy L, et al. Human T-cell lymphotropic virus (HTLV)-related endogenous sequence, HRES-1, encodes a 28-kDa protein: a possible autoantigen for HTLV-I gag-reactive autoantibodies. Proc Natl Acad Sci U S A 1992;89:1939–43. [28] Perl A, Colombo E, Dai H, Agarwal R, Mark KA, Banki K, et al. Antibody reactivity to the HRES-1 endogenous retroviral element
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identifies a subset of patients with systemic lupus erythematosus and overlap syndromes. Correlation with antinuclear antibodies and HLA class II alleles. Arthritis Rheum 1995;38:1660–71. [29] Gergely Jr P, Blazsek A, Danko K, Ponyi A, Poor G. Detection of TT virus in patients with idiopathic inflammatory myopathies. Ann NY Acad Sci 2005;1050:304–13.
Anti-beta2-glycoprotein I antibodies are associated with pregnancy loss in women with the lupus anticoagulant The presence of lupus anticoagulant (LA) predisposes to fetal loss and to venous and arterial thrombosis; however, a subgroup of women is unaffected by pregnancy loss. Currently, no predictive markers are available for the identification of women positive for LA at increased risk for pregnancy loss. The aim of this study by Sailer T. et. al. (Thrombosis 95: 796-801) was to investigate whether increased anti-beta2-GPI-antibodies predict pregnancy loss in women positive for LA. Cross-sectional study was performed in a cohort of 39 women with persistent LA, who had in total 111 pregnancies. Fifteen women had exclusively normal pregnancies (30 pregnancies) and 24 women had pregnancy losses (81 pregnancies). Increased levels of anti-beta2-GPI antibodies were significantly associated with pregnancy loss [odds ratio (OR) 9.6, 95% confidence interval (CI) 1.6-56.4]. This risk was even higher in the subgroup of women (n=16) with more than two miscarriages or fetal loss after the first trimester [OR 13.1, 95% CI 1.4-12.3]. There was no significant association between anticardiolipin antibodies and pregnancy loss [OR 3.5, 95% CI 0.7-17.6]. The co-existence of anti-beta2-GPI and anticardiolipin antibodies was also predictive for pregnancy loss [OR 6.1, 95% CI 1.3-29.7]. It was concluded that increased levels of anti-beta2-GPI antibodies are predictive for pregnancy loss among women positive for LA, and that prophylactic treatment should be considered in these women even without a history of previous pregnancy loss.
Muscarinic receptors autoantibodies purified from mammary adenocarcinoma-bearing mice sera stimulate tumor progression The ability of tumor cells to stimulate adaptive immunity, particularly by inducing anti-tumor antibodies (Abs), has been extensively reviewed. LM3 is a tumorigenic cell line derived from a murine mammary metastatic adenocarcinoma that spontaneously overexpressed mAchR. Here, Fiszman G. et. al. ( Int Immunopharmacol 2006; 8: 1323-30) investigated the ability of Abs purified from the sera of LM3 tumor-bearing mice, directed against muscarinic acetylcholine receptors (mAchR) to modulate tumor cells' proliferation and angiogenesis. The authors observed that IgG from early tumor bearers (ETB), 14-day LM3 tumor, and from late tumor bearers (LTB), 28-day LM3 tumor, displaced tritiated quinuclidinyl benzilatebinding to LM3 tumor cells, confirming Abs interaction with cholinoceptors, while IgG from normal mice did not modify the agonist binding to AchR at any concentration tested. In addition, Abs from ETB and LTB immunoblotted a protein of 70 kDa on murine tumor cells and on heart homogenates that was also recognized by a specific anti-M(2) receptor monoclonal antibody. IgG from LTB-potentiated LM3 cells induced angiogenesis by increasing the number of blood vessels and VEGFA production in peritumoral skin "via" mAchR, in an agonist similar manner. In conclusion, autoAbs purified from LM3 tumor-bearing mice sera exert different pro-tumor actions depending on the stage of tumor development: in ETB, they stimulate tumor cells' proliferation, while in LTB they potentiate tumor neovacularization.
Possible pathogenic nature of the recently discovered TT virus: Does it play a role in autoimmune rheumatic diseases? Peter Gergely Jr. a,b , Andras Perl c , Gyula Poór a,b,⁎ a National Institute of Rheumatology and Physiotherapy, Frankel Leó u. 38-40, H-1023 Budapest, Hungary Musculoskeletal Molecular Biology Research Group, Hungarian Academy of Sciences, Frankel Leó u. 38-40, H-1023 Budapest, Hungary Departments of Medicine, Microbiology and Immunology, State University of New York, Upstate Medical University, College of Medicine, 750 East Adams Street, Syracuse, NY 13210, USA b
c
Available online 19 April 2006
Abstract Pathogenesis of viral origin has long been suggested in autoimmune rheumatic diseases. Beside the well-defined virus induced transient or chronic rheumatic diseases often resembling systemic autoimmune disorders such as rheumatoid arthritis, viruses can contribute to disease pathogenesis by several different pathomechanisms. TT virus is a recently discovered virus of extremely high genetic diversity which commonly infects humans. Despite accumulated evidence on the biological characteristics of TTV, its pathogenicity is still in question; many consider TTV as a harmless endosymbiont. The recent paper overviews the biology of TT virus and investigates the hypothesis that TTV might have a causative role in human diseases with special attention to the possibility that TTV might trigger autoimmunity in rheumatic disorders. © 2006 Elsevier B.V. All rights reserved. Keywords: TT virus; Pathogenesis; Autoimmunity; Rheumatic disorders
Contents 1. Introduction . . . . . . . . . . . . . . . . . 2. Biological characteristics of TTV . . . . . . 3. Possible pathogenicity of TTV . . . . . . . . 4. TT virus in autoimmune rheumatic disorders: 5. Conclusion . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . Take-home messages . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . .
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⁎ Corresponding author. 1st Department of Rheumatology and Metabolic Osteology, National Institute of Rheumatology and Physiotherapy, Frankel Leó u. 38-40, H-1023 Budapest, Hungary. Tel.: +36 1 438 8300; fax: +361 355 2779. E-mail address: [email protected] (G. Poór). 1568-9972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.autrev.2006.03.002
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1. Introduction Autoimmune rheumatic diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), idiopathic
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P. Gergely Jr. et al. / Autoimmunity Reviews 6 (2006) 5–9
inflammatory myopathies (IIM) or systemic sclerosis (SSc) are of unknown etiology. They constitute a heterogeneous group of chronic multisystem inflammatory disorders characterised by involvement of musculoskeletal structures and variably associated with extraarticular manifestations. Several lines of independent evidence indicate that a trigger, possibly a virus operating on the background of strong genetic and hormonal predisposing factors may be involved in their etiopathogenesis. Beside direct pathogenicity in virus-induced arthralgy/arthritis syndromes, a number of different pathomechanisms have been suggested in autoimmune rheumatic diseases. These include molecular mimicry between viral proteins and autoantigens, T or B cell dysfunctions as a result of an inadequate response to the pathogen in the genetically susceptible host or other immunregulatory abnormalities caused by viral proteins [1]. TT virus is a newly identified DNA virus of unknown pathogenicity which commonly infects humans [2]. Although a vast amount of data has been accumulated on its biological characteristics since its discovery in 1997 [3], very few evidences are available regarding the prevalence or possible role of the virus in autoimmune disorders. 2. Biological characteristics of TTV Nishizawa et al. identified TTV by representational difference display analysis in the serum of a Japanese patient with acute post-transfusion hepatitis of unknown etiology in 1997 [4]. The virus was first named after the initials of the patient then was renamed transfusion–transmitted virus. The small DNA virus with a unique unenveloped single-stranded circular DNA genome of negative polarity had originally been classified into the Circoviridae family [5]. Phylogenetic analysis of TTV isolates sourced from different parts of the world demonstrates an extremely high genetic diversity [6]. Due to this fact and difficulties in expression of full-length TTV protein in prokaryotic or eukaryotic cells, and generation of pan-specific TTV antibodies, diagnosis of TTV infection has been dependent on PCR detection of viral DNA using primers specific for the conservative non-coding regions [7]. TTV has earlier been documented in various types of human samples including serum, peripheral blood mononuclear cells, stool, saliva, bile, breast milk or synovial fluid [8,9]. Infection with TTV appears ubiquitous across different human populations, several primate species and in farm animals [10]. Various genotypes of the virus have been detected with frequencies ranging from 2% to 90% in serum of healthy blood donors [11,12]. To date, a culture system capable of supporting adequate replication of TTV has not been available, nor has
the virus been visualized with certainty by electron microscopy. However, TTV has been transmitted to chimpanzees and rhesus monkeys by intravenous inoculation of virus-positive human sera or fecal extracts [13]. Transfection of competent TTV DNA induces mRNA transcription, but not DNA replication, in cultured cells [14]. Despite the increasing amount of data, many aspects of the biology of TTV, i.e. method of replication, antibody production against TTV-derived proteins, significance of its global presence and high genomic variability, cell tropism, replicational and transcriptional regulation have not yet been elucidated. 3. Possible pathogenicity of TTV Since the first isolation of TTV, most studies have focused on its possible role in liver disorders and reported a possible association in fulminant hepatitis, cryptogenic liver disease, non A–G or post transfusion hepatitis, liver cirrhosis and hepatocellular carcinoma [2–4,7]. Higher mortality has also been reported among acute hepatitis patients co-infected with TTV and hepatitis B [3]. The association between liver diseases and TTV, however, seems conflicting. There is a bulk of evidence reporting the absence of such associations. Furthermore, morphological changes within TTV-infected hepatocytes could not be detected [15]. Clinical course and laboratory parameters of patients with hepatitis co-infected with TTV were not different from those without TTV co-infection [16]. Epidemiological associations of TTV with B cell lymphoma and Hodgkin's disease [17], aplastic anemia [18], idiopathic pulmonary fibrosis [19], acute respiratory disease [20] have also been described. TTV infection was also associated with poor clinical outcome in laryngeal cancer in a recent Hungarian study [21] and high TTV viremia was reported to result in decreased survival in HIV positive patients [22]. Although some studies found differences in the biological or possibly pathogenic properties of different genogroups of TTV [21], the significance of the genetic variants is unknown at present. Almost all evidences supporting a role for TTV in human diseases consist of epidemiological surveys; and it has still not been determined whether TTV is capable of causing any human disease. 4. TT virus in autoimmune rheumatic disorders: casual coincidence or causative agent? A few independent studies have provided no compelling evidence that TTV has a pathogenic role in autoimmune hepatitis. In the first study to assess TTV infection rate in rheumatic diseases, a diminished TTV prevalence
P. Gergely Jr. et al. / Autoimmunity Reviews 6 (2006) 5–9
was found in patients with RA in comparison to controls of unselected pathology and in patients with SLE [23]. Seemayer et al. found similar percentage of TTV DNA positivity in serum samples of patients with RA and SSc which was comparable to that of patients with osteoarthritis (OA) and normal blood donors [24]. We were able to identify TT virus DNA in the synovial fluid of patients with RA and OA using a sensitive real-time PCR and melting curve analysis but found the detection rate similar [9]. Recently, a TTV-derived putative protein was shown to induce apoptosis in various human hepatocellular carcinoma cell lines [25]. Although dysregulated apoptosis has been known to play a crucial role in several autoimmune diseases such as SLE, the significance of this finding is to be further confirmed and clarified. We identified novel immunodominant epitopes of the 28 kDa HTLV I-related retroviral element (HRES-1/ p28) autoantigen and investigated their cross-reactivity with antigens of infectious viruses [26]. HRES-1 is an endogenous retroviral element encoding a 28-kDa nuclear autoantigen, HRES-1/p28, which is expressed in a tissue-specific manner [27]. Antibodies to HRES-1/ p28 were detected in 21–50% of patients with SLE and overlap syndromes in various laboratories in contrast to normal donors or HIV-infected patients [28]. Two of the identified immunodominant epitopes showed significant sequence homology to different open reading frames of TTV. In our experiment, all HRES-1/p28-reactive sera recognized at least one TTV-specific peptide. Further, a putative TTV capsid peptide having no homology to HRES-1/p28, was also recognized by the majority of lupus sera. Most prominent reactivity with TTV-derived peptides was associated with the presence of TTV DNA in patients with SLE. We found prevalence of TTV DNA significantly elevated in SLE patients (120/211) with respect to healthy control donors (66/199) or patients with RA (23/91). Interestingly, first-degree healthy relatives of lupus patients (51.3%) had a significantly lower TTV infection rate than lupus patients (66.1%) but a higher infection rate than healthy donors from families without lupus (33.9%). Thus, genetic factors underlying susceptibility to SLE may also influence infection by TTV. In addition to HRES-1/p28 epitopes showing similarity to TTV proteins, lupus sera had strong binding affinity to a peptide showing similarity to the retroviral gag-like region of 70 k U1 snRNP lupus autoantigen suggesting that cross-reactivity of HRES-1/p28 with TTV and 70 k U1 snRNP may lead to epitope spreading and contribute to generation of anti-nuclear antibodies. In a separate study we detected TTV DNA in 61/94 (64.9%) patients with IIM which did not differ
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Table 1 Arguments for and against the hypothesized pathogenic role of TTV in autoimmune rheumatic disorders For
Against
▪ Increased prevalence in SLE vs healthy controls or RA patients ▪ Epidemiological association with severe IIM ▪ Humoral response to TTV specific peptides in SLE ▪ Sequence homology and possible molecular mimicry between immunodominant epitopes of HRES-1 and TTV specific peptides in SLE ▪ Possibility of epitope spreading and generation of anti-nuclear antibodies due to crossreactivity of HRES-1/p28 with TTV and 70 k U1 snRNP ▪ Capability of a TTV-derived putative protein of inducing apoptosis
▪ Global presence in normal population ▪ Inconclusive and conflicting data of epidemiological associations in several diseases ▪ Paucity of data on humoral response against TTV derived proteins ▪ Unknown cause and significance of the extremely high genomic variability ▪ Undetermined differences in biological properties of certain TTV genogroups ▪ Lack of morphological or molecular abnormalities of TTV infected cells ▪ Paucity of data on autoimmune rheumatic diseases ▪ Lack of conclusive data supporting the pathogenic nature of TTV in general
significantly from patients with RA and from healthy individuals [29]. However, patients with more severe IIM had a significantly higher rate of TTV infection indicating that TTV infection might be a prognostic factor in IIM. 5. Conclusion Despite intensive efforts to clarify the pathogenic nature of TTV, the virus could not be causally associated with any disease and many researchers consider TTV an orphan or harmless virus, or even a symbiont. Its causal role in autoimmune rheumatic diseases can be hypothesized based on only a few studies including two of our own. Our data support the notion that molecular mimicry of immunodominant ERV epitopes may confer cross-reactivity with TTV antigens, mediate epitope spreading to self antigens such as the 70 kDa U1 snRNP, and thus contribute to formation of antinuclear autoantibodies in SLE. TTV infection may also be associated with a more severe clinical outcome in patients with IIM. Although arguments against its causative role in human diseases, especially in rheumatic disorders far outweigh the proofs for it (Table 1), pathogenicity of TTV cannot be ruled out. It will be interesting to
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discover whether TTV infected individuals are, indeed, innocent bystanders or there will be ultimate consequences of carrying the virus. This issue is certainly worth further research. Acknowledgement This work was supported by the Hungarian Scientific Research Fund OTKA T042637 and by grants RO1 AI 48079 and FO5 TW05421 from the National Institutes of Health, USA. Take-home messages • Viral etiology has long been suggested in autoimmune rheumatic disorders. • TT virus, a recently discovered virus with extremely high genetic diversity commonly infects humans. • Despite accumulated evidence on the biology of TTV its pathogenicity is unknown. • There are very few evidences supporting its role in autoimmune rheumatic disorders; these include an increased prevalence in SLE and in severe IIM and a possible molecular mimicry between TTV and HRES-1/p28, an endogenous retroviral protein. • At present, TTV is mostly considered as a harmless virus. References [1] Perl A. Mechanisms of viral pathogenesis in rheumatic disease. Ann Rheum Dis 1999;58:454–61. [2] Okamoto H, Nishizawa T, Ukita M. A novel unenveloped DNA virus (TT virus) associated with acute and chronic non-A to G hepatitis. Intervirology 1999;42:196–204. [3] Abraham P. TT viruses: how much do we know? Indian J Med Res 2005;122:7–10. [4] Nishizawa T, Okamoto H, Konishi K, Yoshizawa H, Miyakawa Y, Mayumi M. A novel DNA virus (TTV) associated with elevated transaminase levels in posttransfusion hepatitis of unknown etiology. Biochem Biophys Res Commun 1997;241:92–7. [5] Mushahwar IK, Erker JC, Muerhoff AS, Leary TP, Simons JN, Birkenmeyer LG, et al. Molecular and biophysical characterization of TT virus: evidence for a new virus family infecting humans. Proc Natl Acad Sci U S A 1999;96:3177–82. [6] Bendinelli M, Pistello M, Maggi F, Fornai C, Freer G, Vatteroni ML. Molecular properties, biology, and clinical implications of TT virus, a recently identified widespread infectious agent of humans. Clin Microbiol Rev 2001;14:98–113. [7] Biagini P, Gallian P, Attoui H, Cantaloube JF, Touinssi M, de Micco P, et al. Comparison of systems performance for TT virus detection using PCR primer sets located in non-coding and coding regions of the viral genome. J Clin Virol 2001;22:91–9. [8] Ross RS, Viazov S, Runde V, Schaefer UW, Roggendorf M. Detection of TT virus DNA in specimens other than blood. J Clin Virol 1999;13:181–4.
[9] Gergely P, Blazsek A, Weiszhar Z, Poor G. Relationship between TT virus infection and autoimmune rheumatic diseases. Ann Rheum Dis 2004;63(S1):65–65 (abstract). [10] Leary TP, Erker JC, Chalmers ML, Desai SM, Mushahwar IK. Improved detection systems for TT virus reveal high prevalence in humans, non-human primates and farm animals. J Gen Virol 1999;80:2115–20. [11] Biagini P. Human circoviruses. Vet Microbiol 2004;98:95–101. [12] Huang LY, Oystein Jonassen T, Grinde B, et al. High prevalence of TT virus-related DNA (90%) and diverse viral genotypes in Norwegian blood donors. J Med Virol 2001;64:381–6. [13] Okamoto H, Fukuda M, Tawara A, Nishizawa T, Itoh Y, Hayasaka I, et al. Species-specific TT viruses and cross-species infection in nonhuman primates. J Virol 2000;74:1132–9. [14] Desai MM, Pal RB, Banker DD. Molecular epidemiology and clinical implications of TT virus (TTV) infection in Indian subjects. J Clin Gastroenterol 2005;39:422–9. [15] Rodriguez-Inigo E, Casqueiro M, Bartolome J, Ortiz-Movilla N, Lopez-Alcorocho JM, Herrero M, et al. Detection of TT virus DNA in liver biopsies by in situ hybridization. Am J Pathol 2000;156:1227–34. [16] Watanabe H, Shinzawa H, Shao L, Saito T, Takahashi T. Relationship of TT virus infection with prevalence of hepatitis C virus infection and elevated alanine aminotransferase levels. J Med Virol 1999;58:235–8. [17] Garbuglia AR, Iezzi T, Capobianchi MR, Pignoloni P, Pulsoni A, Sourdis J, et al. Detection of TT virus in lymph node biopsies of B-cell lymphoma and Hodgkin's disease, and its association with EBV infection. Int J Immunopathol Pharmacol 2003;16:109–18. [18] Miyamoto M, Takahashi H, Sakata I, Adachi Y. Hepatitisassociated aplastic anemia and transfusion-transmitted virus infection. Intern Med 2000;39:1068–70. [19] Bando M, Ohno S, Oshikawa K, Takahashi M, Okamoto H, Sugiyama Y. Infection of TT virus in patients with idiopathic pulmonary fibrosis. Respir Med 2001;95:935–42. [20] Maggi F, Pifferi M, Fornai C, Andreoli E, Tempestini E, Vatteroni M, et al. TT virus in the nasal secretions of children with acute respiratory diseases: relations to viremia and disease severity. J Virol 2003;77:2418–25. [21] Szladek G, Juhasz A, Kardos G, Szoke K, Major T, Sziklai I, et al. High co-prevalence of genogroup 1 TT virus and human papillomavirus is associated with poor clinical outcome of laryngeal carcinoma. J Clin Pathol 2005;58:402–5. [22] Christensen JK, Eugen-Olsen J, SLrensen M, Ullum H, Gjedde SB, Pedersen BK, et al. Prevalence and prognostic significance of infection with TT virus in patients infected with human immunodeficiency virus. J Infect Dis 2000;181:1796–9. [23] Maggi F, Fornai C, Morrica A, Casula F, Vatteroni ML, Marchi S, et al. High prevalence of TT virus viremia in italian patients, regardless of age, clinical diagnosis, and previous interferon treatment. J Infect Dis 1999;180:838–42. [24] Seemayer CA, Viazov S, Gay S, et al. Prevalence of TTV DNA and GBV-C RNA in patients with systemic sclerosis, rheumatoid arthritis, and osteoarthritis does not differ from that in healthy blood donors. Ann Rheum Dis 2001;60:806–9. [25] Kooistra K, Zhang YH, Henriquez NV, Weiss B, Mumberg D, Noteborn MH. TT virus-derived apoptosis-inducing protein induces apoptosis preferentially in hepatocellular carcinomaderived cells. J Gen Virol 2004;85:1445–50. [26] Gergely Jr P, Pullmann R, Stancato C, Otvos Jr L, Koncz A, Blazsek A, et al. Increased prevalence of transfusion–transmitted virus and cross-reactivity with immunodominant epitopes of the
P. Gergely Jr. et al. / Autoimmunity Reviews 6 (2006) 5–9 HRES-1/p28 endogenous retroviral autoantigen in patients with systemic lupus erythematosus. Clin Immunol 2005;116:124–34. [27] Banki K, Maceda J, Hurley E, Ablonczy E, Mattson DH, Szegedy L, et al. Human T-cell lymphotropic virus (HTLV)-related endogenous sequence, HRES-1, encodes a 28-kDa protein: a possible autoantigen for HTLV-I gag-reactive autoantibodies. Proc Natl Acad Sci U S A 1992;89:1939–43. [28] Perl A, Colombo E, Dai H, Agarwal R, Mark KA, Banki K, et al. Antibody reactivity to the HRES-1 endogenous retroviral element
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identifies a subset of patients with systemic lupus erythematosus and overlap syndromes. Correlation with antinuclear antibodies and HLA class II alleles. Arthritis Rheum 1995;38:1660–71. [29] Gergely Jr P, Blazsek A, Danko K, Ponyi A, Poor G. Detection of TT virus in patients with idiopathic inflammatory myopathies. Ann NY Acad Sci 2005;1050:304–13.
Anti-beta2-glycoprotein I antibodies are associated with pregnancy loss in women with the lupus anticoagulant The presence of lupus anticoagulant (LA) predisposes to fetal loss and to venous and arterial thrombosis; however, a subgroup of women is unaffected by pregnancy loss. Currently, no predictive markers are available for the identification of women positive for LA at increased risk for pregnancy loss. The aim of this study by Sailer T. et. al. (Thrombosis 95: 796-801) was to investigate whether increased anti-beta2-GPI-antibodies predict pregnancy loss in women positive for LA. Cross-sectional study was performed in a cohort of 39 women with persistent LA, who had in total 111 pregnancies. Fifteen women had exclusively normal pregnancies (30 pregnancies) and 24 women had pregnancy losses (81 pregnancies). Increased levels of anti-beta2-GPI antibodies were significantly associated with pregnancy loss [odds ratio (OR) 9.6, 95% confidence interval (CI) 1.6-56.4]. This risk was even higher in the subgroup of women (n=16) with more than two miscarriages or fetal loss after the first trimester [OR 13.1, 95% CI 1.4-12.3]. There was no significant association between anticardiolipin antibodies and pregnancy loss [OR 3.5, 95% CI 0.7-17.6]. The co-existence of anti-beta2-GPI and anticardiolipin antibodies was also predictive for pregnancy loss [OR 6.1, 95% CI 1.3-29.7]. It was concluded that increased levels of anti-beta2-GPI antibodies are predictive for pregnancy loss among women positive for LA, and that prophylactic treatment should be considered in these women even without a history of previous pregnancy loss.
Muscarinic receptors autoantibodies purified from mammary adenocarcinoma-bearing mice sera stimulate tumor progression The ability of tumor cells to stimulate adaptive immunity, particularly by inducing anti-tumor antibodies (Abs), has been extensively reviewed. LM3 is a tumorigenic cell line derived from a murine mammary metastatic adenocarcinoma that spontaneously overexpressed mAchR. Here, Fiszman G. et. al. ( Int Immunopharmacol 2006; 8: 1323-30) investigated the ability of Abs purified from the sera of LM3 tumor-bearing mice, directed against muscarinic acetylcholine receptors (mAchR) to modulate tumor cells' proliferation and angiogenesis. The authors observed that IgG from early tumor bearers (ETB), 14-day LM3 tumor, and from late tumor bearers (LTB), 28-day LM3 tumor, displaced tritiated quinuclidinyl benzilatebinding to LM3 tumor cells, confirming Abs interaction with cholinoceptors, while IgG from normal mice did not modify the agonist binding to AchR at any concentration tested. In addition, Abs from ETB and LTB immunoblotted a protein of 70 kDa on murine tumor cells and on heart homogenates that was also recognized by a specific anti-M(2) receptor monoclonal antibody. IgG from LTB-potentiated LM3 cells induced angiogenesis by increasing the number of blood vessels and VEGFA production in peritumoral skin "via" mAchR, in an agonist similar manner. In conclusion, autoAbs purified from LM3 tumor-bearing mice sera exert different pro-tumor actions depending on the stage of tumor development: in ETB, they stimulate tumor cells' proliferation, while in LTB they potentiate tumor neovacularization.