AsianScientist (Aug. 23, 2012) – Researchers in the United States have identified an antibody that compromises the immune systems of HIV-negative people, making them susceptible to infections with opportunistic microbes such as nontuberculous mycobacteria (NTM).
The study findings appear online today in the New England Journal of Medicine.
Based on clinical studies conducted at hospitals in Thailand and Taiwan, the researchers found that the majority of study participants with opportunistic infections made an antibody against interferon-gamma (IFN-gamma), a cell-signaling molecule thought to play a major role in clearing harmful infections.
Nontuberculous mycobacteria are close relatives of the bacterium that causes tuberculosis and can cause severe lung disease. These and other opportunistic infections are common in people with immune deficiency diseases, such as AIDS, but they are rare in people with healthy immune systems.
The first cases were reported in 2004, when researchers in Southeast Asia reported several cases of NTM infections in people with no known problems with their immune systems. The cause of the condition is unknown, but it does not appear to be contagious.
Led by Dr. Sarah Browne of the National Institute of Allergy and Infectious Diseases (NIAID) and Dr. Peter Burbelo of the National Institute of Dental and Craniofacial Research (NIDCR), the study enrolled 203 people, ages 18 to 78 years old.
Of these participants, 52 had NTM infections, 45 had other opportunistic infections with or without NTM co-infection, 58 had tuberculosis, and 48 were healthy volunteers. All participants were HIV-negative.
Examination of participant blood samples for antibodies to cell-signaling molecules such as IFN-gamma showed that 88 percent of the people with NTM or other opportunistic infections had antibodies that blocked their own IFN-gamma (called autoantibodies).
The autoantibodies inhibited IFN-gamma function, hindering the immune system’s ability to clear infection, causing a syndrome that made these study participants more vulnerable to opportunistic infections.
Clues such as the average age of disease onset (50 years) and similarity in ethnic background (Asian, or Asia-born) have led the researchers to speculate that the antibodies are “triggered” as a result of combined genetic and environmental factors. More work is needed to determine why people in Southeast Asia appear to be predisposed to the development of this autoimmune condition.
The study authors also believe that it may be possible to treat the underlying problem by targeting the cells that make the IFN-gamma autoantibodies.
The article can be found at: Browne SK et al. (2012) Adult onset immunodeficiency in Thailand and Taiwan.
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Source: NIAID; Photo: Sanofi Pasteur/Flickr.
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