Signs of infection with Mycobacterium abcessus, which
primarily attacks those with suppressed immune systems
In 2004, medical researchers began noticing cases where patients, primarily middle-aged Asians, sought treatment for frequent opportunistic infections. Developing these infections, which mainly affect people with compromised immune systems, is a key sign of AIDS, and yet these patients test negative for HIV, the AIDS virus.
According to a new study published in the New England Journal of Medicine, an autoimmune response—when your immune system attacks your own body—triggers the immunodeficiency. But we still don’t know why the autoimmune response develops abruptly at around age 50.
For the NEJM study, the researchers wanted to see whether these patients, when compared with healthy subjects and with people who had other infections, had anything unusual going on in their blood. 203 HIV-negative Thai and Taiwanese volunteers, to that end, provided medical histories and blood samples to researchers from the National Institutes of Health. Some participants were currently struggling with at least one opportunistic infection, such as Mycobacterium abcessus. Others acted as controls: Some had tuberculosis, which is related to M. abcessus, and showed no signs that their infection was due to an immunodeficiency, while others were healthy.
By comparing the blood samples from each group, researchers managed to finger the culprit behind the new syndrome: an antibody that tells the immune system to attack the protein interferon-gamma was present in high concentrations in the blood of 88 percent of subjects with the immunodeficiency, but only had an insignificant presence in the control subjects, or was absent entirely. Interferon-gamma is a helpful protein that normally helps the body fight off infections. But for some reason, in these people, the immune system has begun treating it as an enemy.
The researchers still don’t know why the patients’ immune systems begin turning on them, but because the syndrome primarily targets Asians and doesn’t set in until middle age, it may be due to a combination of genetic background and genetic damage from environmental factors. Though the new syndrome’s cause remains mysterious, the study has discovered enough information for researchers to begin treating patients by shutting down the cells that produce anti-interferon-gamma antibodies.