Molecular parameters for precise diagnosis of asymptomatic Epstein-Barr virus reactivation in healthy carriers

Abstract

Asymptomatic Epstein-Barr virus (EBV) reactivations periodically occur in oral mucosa-associated lymphoid tissues. Until now, EBV reactivation has been diagnosed by serologic profiles that suggest virus replication. Serologic responses, however, are delayed and do not necessarily indicate ongoing replicative activity. The aim of the present study was to establish in healthy carriers parameters for a molecular diagnosis of reactivated EBV infection. Recent studies emphasized the association of an increase in peripheral-B-cell viral load with replicative activity at remote sites. Therefore, real-time PCR was used to quantitate EBV genomes in the peripheral blood mononuclear cells (PBMC) (viral load) and plasma samples (viremia) of 22 healthy EBV-seropositive blood donors over a period of 15 months. Furthermore, transcription of the immediate-early gene encoding BZLF1 was investigated in the PBMC of all volunteers. Serology suggested reactivation in nine donors, of whom all but one showed at least once a significant increase in viral load. Another five individuals also exhibited significant changes in viral load but no serologic response. Of the 13 volunteers with significant increases in viral load, 6 had a period of viremia accompanying the rise in viral load. A stable viral load without viremia and negative serology was seen in eight adults. BZLF1 mRNA was undetectable throughout. We conclude that for healthy subjects serology underestimates the frequency of asymptomatic EBV reactivations. Prospective examination of peripheral viral load and viremia is suitable for the exact diagnosis of EBV reactivation, which might be of advantage for immunocompromised patients in whom EBV reactivations are considerably harmful.

FIG. 1.

Effect of β-actin cDNA coamplification on ZEBRA cDNA amplification efficiency and detection limit by using multiplex real-time PCR. C_t, cycle of threshold; error bars, SD.

FIG. 2.

Group I contains donors who again exhibit a detectable viral load and have serologic evidence of EBV reactivation during 15 months of follow-up.

FIG. 3.

Group II contains donors with serologic evidence of EBV reactivation and significant increases in viral load during 15 months of follow-up (except donor U, who did not show obvious changes in viral load). Black circled values of viral load represent obvious peak values not considered for calculation of the mean individual viral load (indicated by dotted lines; the upper threefold SD of the mean is indicated by short dashes).

FIG. 4.

Virologic parameters in donors without serologic evidence of EBV reactivation but significant changes in viral load and viremia.

FIG. 5.

Donors without serologic or virologic evidence of reactivated EBV infection. Mean individual viral loads are indicated by dotted lines; the upper threefold SD of the mean is indicated by short dashes.