Adult-Onset Immunodeficiency
A patient with Adult-Onset Immunodeficiency has symptoms similar to those caused by an opportunistic infection. National Institute of Allergy

Researchers have pinpointed the disease behind a rash of cases in Taiwan and Thailand where people exhibit AIDS-like symptoms but are not infected with HIV.

A team led by National Institute of Allergy and Infectious Diseases researcher Sarah Browne studied more than 200 patients showing signs of the mysterious illness, and it found that the affected persons were making antibodies against a key component of their own immune system. The disease, which the researchers dubbed "Adult-Onset Immunodeficiency" in a paper published in the New England Journal of Medicine on Thursday, is not caused by a virus, meaning it is not contagious.

The researchers found that 88 percent of the patients had antibodies in their blood that were designed to target a protein called interferon-gamma.

"Interferon-gamma is a protein produced by the immune system that helps stimulate other immune cells to fight infection," Browne said in a phone interview. "When you block that you don't have proper infection-fighting capabilities."

The patients in question had fallen victim to opportunistic microbes like nontuberculous mycobacteria -- a close relative of tuberculosis that can cause severe lung disease -- which prey on people with weakened immune systems.

Browne and her colleagues still don't know what triggered the patients' autoimmune disease, or why it seems to have cropped up in Southeast Asia.

The newly identified disease is one of many kinds of conditions where a person's immune system engages in friendly fire. Crohn's disease and rheumatoid arthritis are some classic examples of autoimmune disease, where the immune system attacks the gut and the joints, respectively. But conditions where the immune system turns on itself, though not unheard of, are rarer, according to Browne.

Among the recently discovered conditions where a good immune system turns on itself, "I would say this is the largest one," Browne said.

SOURCE: Browne et al. "Adult-Onset Immunodeficiency in Thailand and Taiwan." NEJM 367: 725-734, 23 August 2012.