Productive infection of CD4+ and CD8+ mature human T cell populations and clones by human herpesvirus 6. Transcriptional down-regulation of CD3

The susceptibility to infection by human herpesvirus 6 (HHV-6) of mature human T lymphocytes belonging to the two major subpopulations (i.e., CD3+ CD4+ CD8- and CD3+ CD4- CD8+) was investigated by using CD4+ or CD8+ T cell populations and clones derived from normal adult peripheral blood. Productive HHV-6 infection was observed in both CD4+ and CD8+ T cells. By days 2 to 6 after infection, increasing numbers of cells exhibited characteristic morphologic alterations, becoming enlarged, uniformly rounded and refractile as a consequence of the virus-induced cytopathic effect. During the course of HHV-6 infection, analysis of the surface membrane phenotype of the T cell populations and clones revealed a progressive decline in the expreson of the CD3/TCR complex, whereas other T cell-ssociated markers (e.g., CD2) were unaffected. Northern blot analysis of mRNA extracted from HHV-6-infected T cells demonstrated a dramatic loss of the specific messages for the γ-, δ-, and ε-chains of CD3. Infection by HHV-6, but not by HSV-or human CMV, elicited CD3/TCR down-regulation also in the neoplastic T cell line Jurkat. The down-regulation of CD3/TCR was dependent upon live virus infection, because previous inactivation of HHV-by heat (56°C for 1 h) or UV light (16 J/m2) totally abrogated the effect. Expression of the immediate early or early genes of HHV-6 was not sufficient to induce CD3/TCR modulation, as indicated by studies with the viral DNA polymerase inhibitor phosphonoformic acid. The observation that both major subsets of mature TCR-αβ+ T lymphocytes are susceptible to HHV-6 infection indicates that this virus may have a broad spectrum of activity on the immune system. The transcriptional down-regulation of the CD3/TCR complex, by affecting a critical T cell recognition function, could be relevant to HHV-6 pathogenesis.