Herpesvirus decimates immune-cell soldiers.

Natural killer cells are the foot soldiers of the immune system. These white cells home in on virus-infected cells, lock onto their target, and deliver chemicals that can kill the target ceil. If the killer cells real function or are killed themselves, an important component of the immune attack is diminished.

Virologists blame herpes viruses for a number of human ills, ranging from cold sores to heart disease (see p. 216). Now, laboratory studies by researcher Paolo Lusso and his colleagues suggest that infection with herpesvirus-6 can dampen the body's natural-killer-cell response. In fact, the new findings hint that infection with this herpesvirus may play a role in immune illnesses such as AIDS.

In 1989, Lusso's team showed that herpesvirus-6 attacks another kind of white cell, the CD4 T-lymphocyte (SN: 1/28/89, p. 55). AIDS researchers know that such T-lymphocytes are the primary target of the AIDS-causing human immunodeficiencyvirus (HIV). In the April 1 NATURE, Lusso's team demonstrates that herpesvirus-6 also infects and destroys natural killer cells, which are known to function abnormally in HIV-infected people.

It is the first time that researchers have shown that natural killer cells are vulnerable to any kind of viral attack, comments researcher Anthony L. Komaroff of Harvard Medical School in Boston. The finding suggests that rather than being killed itself, herpesvirus-6 can turn and annihilate its immune-cell attacker, at least in the test tube, says Lusso, who is at the National Cancer Institute in Bethesda, Md. The team has yet to prove that herpesvirus-6 performs the same way in the body

Lusso's team also made another surprising discovery: They found that the herpes-infected natural killer cells manufacture the CD4 receptor molecule that provides a port of entry for HIV.. CD4 T-lymphocytes express this surface receptor and thus are vulnerable to HIV infection. However, natural killer cells do not normally produce the CD4 molecule and thus are typically impervious to HIV's attack. Yet, when Lusso's group added HIV to cultures of herpes-infected natural killer cells, they found that HIV could infect those cells.

The research raises the intriguing possibility that this type of herpesvirus helps destroy the immune system by making natural killer cells vulnerable to HIV, Lusso says. The findings also suggest that herpesvirus-6 may work in tandem with HIV to produce a more aggressive illness, he says.

Lusso's results fit with previous research on chronic fatigue syndrome, another immune illness in which natural killer cells don't function properly Harvard's Komaroff speculates that herpesvirus-6 may cause the killer-cell dysfunction observed in people with this syndrome. His research has shown that chronic fatigue patients are likely to exhibit an active infection with herpesvirus-6. Most people carry this type of herpesvirus, but the virus usually remains inactive, he adds.