Prevalence and cellular reservoir of latent human herpesvirus 6 in tonsillar lymphoid tissue

There are few studies that examine prevalence, quantity, and cellular procl ivity of latent human herpesvirus 6 (HHV-6) in healthy populations. We exam ined 69 tonsils with paired blood specimens from children without evidence of acute infection. By polymerase chain reaction (PCR), HHV-6 was detected at low levels in 100% of tonsils and 39% of blood samples (n = 27), suggest ing that prevalence of latent HHV-6 infection is high in children and may b e underestimated by PCR analysis of blood. Although HHV-6A and HHV-6B were detected, HHV-6B predominated, being found in 97% of samples (n = 67). Tons il sections from 7 cases were examined by in situ hybridization using 2 HHV -6 probes and immunohistochemical analysis. Using both in situ hybridizatio n and immunohistochemical analysis, all tissues revealed marked HHV-6-speci fic staining in the squamous epithelium of the tonsillar crypts and rare po sitive lymphocytes. We conclude that HHV-6 is present universally in tonsil s of children, and tonsillar epithelium may be an important viral reservoir in latent infection.