Rev. Bras. Hematol. Hemoter. vol.37 número6

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rev bras hematol hemoter. 2015;37(6):357–358

w w w . r b h h . o r g

Revista

Brasileira

de

Hematologia

e

Hemoterapia

Brazilian

Journal

of

Hematology

and

Hemotherapy

Scientific

Comment

Torque

teno

virus:

a

ubiquitous

virus

夽

Karen

Brajão

de

Oliveira

∗

UniversidadeEstadualdeLondrina(UEL),Londrina,PR,Brazil

Torquetenovirus(TTV)isanon-envelopedhumanDNAvirus isolatedbyNishizawaetal.in1997.1_TTV,_recently_classified

astheAlphatorquevirusgenuswithintheAnelloviridaefamilyby theInternationalCommitteeonTaxonomyofViruses(ICTV), wasthefirsthumanviruswithasingle-strandedcircularDNA genometobeidentified.2_Thus_far,_five_main_genetic_groups

(Groups1–5)involvingatleast39genotypeshavebeen identi-fiedbasedonphylogeneticanalysis.3

The TTV genome can be divided into an untranslated region(UTR)of1.2kbandapotentialcodingregionof2.6kb. The UTR is relatively conserved, suggesting that it plays an importantregulatory role in viral replication. The cod-ingregioncontainstwolargeopenreadingframes:ORF1and ORF2.Severalotheropenreadingframeshavebeendescribed, andthepeptidesthattheyencodedifferinlengthfordifferent isolates.4

Thisvirus is characterizedbyanextremely high preva-lence,withrelativelyuniformdistributionworldwideand a high level of genomic heterogeneity.4 _Although _this _virus

hasaveryhighprevalenceinthegeneralpopulationacross theglobe,neitheritsinteractionwithitshostsnoritsdirect involvementintheetiologyofspecificdiseasesisfully under-stood.

After the discovery of TTV, its detection has been by polymerasechainreaction(PCR) withprimerstargetingthe ORF1(N22region,thefirstdescribedsequence),nevertheless primersderivedfromtheN22regioncandetectonlyaportion of TTV variants mainly representing genetic group 1 TTV (Genotypes1–6).5,6_As_the_UTRs_of_the_viral_genome_are_more

conservedwhencomparedtotheORFregions,UTR-targeting primers(usedlaterforthedetectionofTTVDNA)candetect

DOIoforiginalarticle:http://dx.doi.org/10.1016/j.bjhh.2015.07.005.

夽

SeepaperbyMazzolaetal.inRevBrasHematolHemoter.2015;37(5):336–40.

∗ _{Corresponding}_author_at:_Departamento_de_Ciências_{Patológicas,}_Universidade_Estadual_de_Londrina,_Campus_{Universitário,}_86051-970

Londrina,PR,Brazil.

E-mailaddress:karen.brajao@gmail.com

essentiallyallknownTTVstrainsreported,therebydetectinga largernumberofgenotypesgivingahigherdetectionrate.5,7,8

In this issue of the Revista Brasileira de Hematologiae Hemoterapia, there is an important study entitled “Preva-lenceofTorquetenovirusinhealthydonorsofParanáState, southernBrazil”.Inthisarticle,theauthorsdemonstratedthe prevalenceoftheTTVinhealthydonorsinthenorthernand northwesternregionsofthestateofParaná,southernBrazil, bynestedPCRusingasetofprimersfortheN22region.9

TheauthorsdemonstratedahighprevalenceofTTV(69%) amonghealthyblooddonorsbyusingprimerstargetingthe N22region.Itisthereforepossiblethatiftheauthorshadused primersforthe UTRstheprevalencewould havebeeneven higher.

Thishigh prevalenceofthe virusmakesitalmost ubiq-uitousinthehumanpopulationandabletoevadeclearance by the host immune response thereby establishing long-termpersistentinfections.10_In_this_context_we_can_highlight

theMicroRNAs(miRNAs), small22ntnoncodingRNAsthat direct posttranscriptional gene regulation, that have been recognized as important regulators of gene expression in many eukaryotes and even in viruses.11 _Emerging _themes

ofviral miRNAfunctionincludeimmune evasion, prolong-ing longevity of host cells, and regulation of persistent infection.12–14

The TTV makes use of viral miRNAs to modulate the innateimmuneresponseand promoteits persistence. Kin-caidetal.15_showed_that_the_TTV_encodes_a_miRNA_in_vivo_that

targetsN-myc(andSTAT)interactor(NMI),thusmediatinga decreasedresponsetointerferonsandincreasedcellular pro-liferationinthepresenceofinterferon.Thesefactssupportthe

http://dx.doi.org/10.1016/j.bjhh.2015.07.009

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revbrashematolhemoter.2015;37(6):357–358

theorythatmiRNA-mediatedimmuneevasioncontributesto theimmenseubiquityofthesevirusesbyantagonizingthe hostantiviralresponse.

IthasbeensuggestedthatTTVinfectionisassociatedwith manydiseases,howeverthereisnodirectevidenceoflinks betweeninfection and specific clinical diseases,and many questionsremaintobeclarifiedforexample,howcanTTV interfereinmanypathologicalprocessesandinthe dysregu-lationoftheimmunesystem?Thesequestionsundoubtedly representrichfieldsforresearchonTTV.

Conflicts

of

interest

Theauthordeclaresnoconflictsofinterest.

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humantorquetenovirusencodesamicroRNAthatinhibits