Scientists said they have found a new virus that appears to be a cousin of the AIDS virus in people stricken by an autoimmune disease, but other researchers urged caution in linking such disorders to viruses.

A team from Tulane University School of Medicine in New Orleans, Baylor College of Medicine in Houston and Cambridge Biotech Corp. in Rockville, Md., said Thursday it detected the new virus in patients with Sjogren's syndrome, a so-called autoimmune disorder that creates severe dryness of the eyes and mouth.Autoimmune diseases occur when a person's immune system malfunctions and starts attacking the body's own tissues as if they were harmful microbes or viruses.

The new virus, called human intracisternal A-type retroviral particle or HIAP, and the AIDS-causing human immunodeficiency virus both belong to a family of viruses called retroviruses, researchers said. Retroviruses, like other viruses, cannot reproduce without infecting cells. But unlike other viruses, retroviruses are made of RNA rather than DNA, and have the power to permanently insert their genetic information into a host's cell.

Dr. Robert Gallo, the National Cancer Institute researcher credited with co-discovery of the AIDS virus, called the findings an "interesting" preliminary report.

"But there is no evidence that this particle is indeed the cause of this particular disease," Gallo said.

Gallo said that although such particles do indicate retroviral infection, they have never been found before in humans and have not been proven to cause disease in mice or other animals where they are often found.

Dr. Robert Fox, an autoimmune disease expert at Scripps Clinic and Research Foundation in La Jolla, Calif., also noted previous findings suggesting a viral cause of multiple sclerosis and chronic fatigue syndrome have fallen by the wayside.

"Any clue into the underlying etiology (cause) of disease is welcome. But it is necessary to use extreme caution when linking human autoimmune disease to specific viruses or you may needlessly alarm patients and their families," Fox said.

The Tulane researchers first suspected an AIDS-like retrovirus may play a role in autoimmune diseases when it found about one-third of people with Sjogren's syndrome, juvenile rheumatoid arthritis, scleroderma and systematic lupus erythematosus tested positive on certain tests for the HIV virus even though they were not actually infected with HIV. It was theorized such patients were producing antibodies to fight a retrovirus that was related, but not identical, to HIV.

Fox said his team could not duplicate those results in three attempts.

Now, in a study published in the journal Science, the Tulane team reports it has isolated a new retrovirus in laboratory-grown white blood cells exposed to salivary gland tissue from Sjogren's syndrome patients.

Robert Garry, an immunology professor at Tulane, emphasized the discovery does not prove that the virus, called HIAP, causes Sjogren's syndrome or any other autoimmune disorder.

"But we are hopeful we have found the cause because these are serious problems," Garry said.