Human herpesvirus 6 inhibits the proliferative responses of human peripheral blood mononuclear cells

Human herpesvirus 6 (HHV-6) was recently isolated from the blood of immunosuppressed individuals and children with exanthem subitum. In this study, the effect of HHV-6 on the proliferative response of human peripheral blood lymphocytes was tested. T cell lines or human peripheral blood lymphocytes were infected with HHV-6 variant A, strain GS, or variant B, strain Z29. Infected and uninfected cell lysates were UV inactivated and sonicated; when lysates were added to peripheral blood mononuclear cells from HHV-6-seropositive adults, lymphoproliferative responses to antigens (tuberculin purified protein derivative or mumps) and mitogens (phytohemagglutinin or interleukin-2) were inhibited in a dose-dependent manner. This inhibition was reversed by a rabbit anti-HHV-6(GS) antiserum, and inhibition was not due to cell lysis induced by viral infection, since cell death was not observed. This in vitro suppression of cellular immune responses by HHV-6 proteins may be relevant to the in vivo pathogenesis of HHV-6 and its relationship to human diseases.