In order to establish a reliable method for the detection of human herpesvirus-6 (HHV-6) B
antigens in peripheral blood mononuclear cells (PBMCs) collected from HHV-6 infected patients, we created a polyclonal antibody against the HHV-6 B U90
protein (IEA/ex3) and used it to examine the expression of this
protein in virus-infected cells and patients' PBMCs. This antibody reacted with 170 and 195 kDa
proteins in HHV-6 B-infected cord blood mononuclear cells. The IEA/ex3
antigen was detected in cord blood mononuclear cells at 6 hr post-
infection, and the number of infected cells reached its maximum at 48 hr post-
infection. The
antigen stained in a punctate pattern and partially localized to the promyelocytic
leukemia (PML)
protein body. We also examined 60 PBMC samples from 60 febrile children (3-19 months old) and detected IEA/ex3
antigen in the PBMCs by
laser-scanning microscopy. HHV-6 was isolated from 31 of the 60 samples. The sensitivity and specificity of the
antigen detection were 84% (26/31) and 97% (28/29), respectively, in the samples with virus detected. The mean number of
antigen-positive PBMCs was 409/10(6) cells in 20 samples with viral isolation. A significant correlation (r = 0.566; P = 0.008) was observed between the viral load and number of
antigen-positive cells. Although IEA/ex3
antigen was detected by
laser-scanning microscopy in PBMCs (without cultivation) collected from six patients with isolated virus, it was detected in only one sample by conventional fluorescence microscopy. Increasing the intensity by cultivation (24 hr) resulted in a higher detection rate (5/6) even by conventional fluorescence microscopy, which is available in most hospital laboratories.