Abstract
Human herpesvirus-6B (HHV-6B), a causative
agent of exanthem subitum, infects human adult T
cell leukemia (ATL) cell lines. We established a persistent
HHV-6B infection in an ATL cell line, TaY, in
the presence of 20 units/ml interleukin-2 (IL-2).
The HHV-6B infected culture proliferated with a
constant ratio of infected (1%) to the uninfected
(99%) cells. When the IL-2 concentration was
reduced to 5 units/ml, the number of infected cells
in the culture increased transiently by 60% in 11
days, a new balance of 25% infected cells and 75%
uninfected cells was established thereafter. PCR
analysis confirmed a 125-fold increase in the
amount of viral genome in the culture, while the
treatment with ganciclovir reduced the proportion
of infected cells, indicating that an efficient replication
of virus was induced in the culture. Both of
these cultures were maintained in the presence of
20 or 5 units/ml IL-2 over one year without loss of
infected cells. Interestingly, we found that cultures
containing the infected cells grew significantly
faster than the parental uninfected cells at
the same concentration of IL-2. The infected culture
continued to grow for 7 days even in the absence of
IL-2. Because the infection induces cell cycle
arrest, these results indicate that the HHV-6B-infected
ATL cells stimulate the growth of the
uninfected cells during persistent infection in culture.
