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. Objectives: 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 subtractions as well as in corresponding peripheral blood mononuclear cells (PBMCs). Study design: 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 subtractions from all samples whereas HHV-6 DNA was detected in 13 P1, 12 P2, 10 S fractions, and HHV-7 DNA in only one PI fraction. Accordingly, median HHV-6 DNA load was significantly higher in PI than in P2 and S fractions. The detection of HHV-6 DNA in plasma subtractions was statistically associated with a higher HHV-6 viral load in PBMCs (p <= 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. (c) 2007 Elsevier B.V. All rights reserved.