Human herpesvirus-6 (HHV-6) DNA in plasma reflects the presence of infected blood cells rather than circulating viral particles.
BACKGROUND
The presence of HHV-6 DNA in plasma or serum is considered a good marker of active infection. However, it is ignored whether this DNA corresponds to virus particles produced by lymphoid tissue infection or virus-free DNA released from infected circulating blood cells.


OBJECTIVE
To investigate whether HHV-6 DNA in whole plasma is nonencapsidated and its amount is correlated to cellular and human herpesvirus-7 (HHV-7) DNA loads in plasma subfractions as well as in corresponding peripheral blood mononuclear cells (PBMCs).


METHODS
Whole plasma samples from immunocompromised patients were submitted to a DNase-resistance test. Plasma samples from a second group of patients were split up into three subfractions: P1 (pellet of clarification), P2 (pellet of ultracentrifugation), and S (supernatant of ultracentrifugation). HHV-6, HHV-7, and cellular DNA loads were determined in each fraction and PBMCs using specific real-time PCR.


RESULTS
Among 14 whole plasma samples, the majority of HHV-6 DNA detected was unprotected against DNase, i.e. nonencapsidated. The study of 35 other plasma samples revealed that cellular DNA was present in all subfractions from all samples whereas HHV-6 DNA was detected in 13 P1, 12 P2, 10 S fractions, and HHV-7 DNA in only one P1 fraction. Accordingly, median HHV-6 DNA load was significantly higher in P1 than in P2 and S fractions. The detection of HHV-6 DNA in plasma subfractions was statistically associated with a higher HHV-6 viral load in PBMCs (p<or=0.0003).


CONCLUSIONS
Taken together, these data tend to favour the hypothesis of a release of HHV-6 and cellular DNA into plasma following the lysis of infected PBMCs. HHV-6 DNA in plasma does not necessarily reflect the amount of virus produced by the active infection of distant lymphoid tissue and organs.
Achour
Abla
A
Laboratoire de Virologie, Université Pierre et Marie Curie-Paris6 EA 2387, Groupe Hospitalier Pitié-Salpêtrière, Université Paris 6, Paris, France.
Boutolleau
David
D
Slim
Amine
A
Agut
Henri
H
Gautheret-Dejean
Agnès
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001773:Blood Cells / Q000821:virology*; D002648:Child; D002675:Child, Preschool; D004279:DNA, Viral / Q000097:blood*; D003851:Deoxyribonucleases / Q000378:metabolism; D005260:Female; D015654:Herpesvirus 6, Human / Q000235:genetics / Q000302:isolation & purification*; D016199:Herpesvirus 7, Human / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D016867:Immunocompromised Host; D007223:Infant; D007231:Infant, Newborn; D007963:Leukocytes, Mononuclear / Q000821:virology; D008297:Male; D008875:Middle Aged; D010949:Plasma / Q000821:virology; D016133:Polymerase Chain Reaction; D019349:Roseolovirus Infections / Q000821:virology*; D014461:Ultracentrifugation; D019562:Viral Load; D014766:Viremia; D014771:Virion / Q000302:isolation & purification
D004279:DNA, Viral; D003851:Deoxyribonucleases