Electronmicroscopic study of human herpesvirus 6-infected human T cell lines superinfected with human immunodeficiency virus type 1.

Human herpesvirus 6 (HHV-6) has been proposed as one of the co-factors responsible for the development of acquired immunodeficiency syndrome (AIDS) in human immunodeficiency virus (HIV) carriers. We analyzed the interaction between HHV-6 and HIV-1 in superinfected cells. Cell-free HIV-1 could superinfect human T cell lines, MT-4 and Molt-4, which had been previously infected with HHV-6. Both HHV-1 and HHV-6 replicated in the same cells. We observed two types of morphologically distinguished cells as early as 4 days after superinfection. One type (D) was degenerate cells with intracellular and extracellular HHV-6 and with less HIV-1 virions. The other type (I) was relatively intact cells with both HIV-1 and HHV-6 virions. Replication of HIV-1 was more active in the type I as compared with type D cells. The level of HIV-1 reverse transcriptase (RT) activity in the culture supernatants of cells superinfected on day 0 declined after day 7, while that in the supernatants of cell cultures infected with HIV-1 alone remained high between days 12 and 40. These results suggest that the superinfection of the HHV-6-infected cells with HIV-1 may induce a degenerative process in these cells.