Latent infection of human herpesvirus 7 in CD4⁺ T lymphocytes

To determine the cell populations in peripheral blood that are infected latently with human herpesvirus 7 (HHV-7), the real-time polymerase chain reaction (PCR) was used to determine the quantities of viral DNA in adherent and non-adherent cells from 71 healthy volunteers. Real-time PCR, which detected the U31 gene of HHV-7, was developed to measure viral load. The majority of non-adherent cells (14/16; 87.5%) contained HHV-7 DNA, while most of the adherent cells did not (1/16; 6.3%). HHV-7 viral load in non-adherent cells was significantly higher than that in adherent cells (P<0.0001). Then, HHV-7 DNA load was compared between the CD4-positive and -negative cell fractions derived from the non-adherent cells of 26 healthy adults. As in the previous experiment, only 2 (7.7%) of the 26 adherent cell specimens contained small amounts of HHV-7 DNA (27.7 copies/1 × 10⁶ cells and 208.7 copies/1 × 10⁶ cells). In contrast, 88.5% of CD4⁺ T cell samples (23/26 specimens) were positive for HHV-7 DNA, ranging from 0.4 to 3,542.8 copies/1 × 10⁶ cells. Viral DNA was detected in only 3 (11.5%) of the 26 CD4^- T cell specimens, with 8.4, 63.5, and 74.1 copies/1 × 10⁶ cells. HHV-7-positive DNA loads were significantly higher in the CD4⁺ T cells than those observed in the CD4^- T cells (P=0.0005). The relationship between HHV-7 viral loads in non-adherent cells and those in saliva was investigated. Comparison of HHV-7 DNA load between blood CD4⁺ T cells and saliva revealed that the HHV-7 DNA load in saliva correlated with that present in CD4⁺ T cells (r=0.415; P=0.0174).