WASHINGTON -- Researchers have discovered a new virus that resembles the AIDS virus and that may be linked to diseases of the immune system.
The discovery is a retrovirus, a class of viruses that implant themselves in cells and cause disease much later. It is only the third human retrovirus ever discovered.
Until recently retroviruses, common in some animals, were unknown in people.
Researchers said the discovery suggested that the retroviruses might play a larger role in human disease than had been thought.
The finding is reported in today's issue of the journal Science by Dr. Robert F. Garry of the Tulane University Medical School.
Other researchers said the new virus was particularly intriguing because, like the retrovirus that causes AIDS, it appeared to involve disorders of the immune system. (The third human retrovirus causes a kind of leukemia.)
"It is clear that this is a new human retrovirus he has isolated," said Dr. Richard Young of the Whitehead Institute for Biomedical Research. "It hasn't been proved that it is the cause of autoimmune diseases, but it is at least linked to them," he said. "It makes you think about new approaches to human disease."
Because the new retrovirus resembles the AIDS virus, its existence may help explain why some patients falsely test positive for AIDS.
Some scientists reacted cautiously to the announcement, saying that more proof was needed that the virus came from the human tissue Dr. Garry worked with and not from the culture in which it was grown.
But if the finding that this particular virus causes disease is correct, experts said, it will be a major advance in the study of viruses that cause human disease.
"This will create a great deal of interest among scientists and could be very important," said Dr. Bernard Moss, a virologist at the National Institute of Allergy and Infectious Diseases. "It is a very interesting result that needs confirmation, but raises the possibility that we are only looking at the tip of the iceberg in terms of human retroviruses."
Human retroviruses have been known only in the past two decades. One variety, discovered by Dr. Robert C. Gallo at the National Cancer Institute, can cause leukemia, and the other, of which Dr. Gallo was co-discoverer, causes acquired immune deficiency syndrome.
The new retrovirus may be the cause or may help find the cause of several chronic diseases, including Sjogren's syndrome, a disorder of the tear ducts and salivary glands; lupus; and one variety of rheumatoid arthritis. All three are believed to result from malfunctioning of the immune system.
Dr. Garry said he took samples of tissue from six patients who have Sjogren's syndrome. When he grew them in laboratory cultures, he found virus particles that had some properties similar to human immunodeficiency virus, the AIDS virus.
He called the new virus a distant cousin of HIV and said that while he has not yet proved that it was the cause of Sjogren's syndrome, it was a logical candidate.
Dr. Garry began his work with a mystery: Why may patients with certain diseases, including Sjogren's, lupus and rheumatoid arthritis, appear to be infected on AIDS blood tests?
Dr. Garry and others suspected that the reason for the false positives might be that these other diseases were also caused by an agent very like HIV.
The discovery fits well with a new theory that helps explain some immune system diseases. The immune system attacks not only foreign particles in the body, the theory goes, but also the body's own cells if they show signs of attack by a virus or bacteria.
The body's attack on its own cells may go out of control when triggered by retroviruses.