An AIDS-associated microbe unmasked.

An AIDS-Associated Microbe Unmasked

Scientists who isolated a mysterious infectious agent in 1986 from a deceased AIDS patient now identify the organism as a type of mycoplasma -- a life form representing an intermediate step between viruses and bacteria. Using tagged antibodies and pieces of the mycoplasma's DNA, they have found the organism in 22 of 32 deceased AIDS patients and in placentas delivered from two pregnant women with AIDS. It also appeared in tissues from six AIDS-free individuals who died of an unidentified illness.

The newly identified microbe, which the researchers call Mycoplasma incognitus, can cause widespread, fatal tissue damage in humans and laboratory monkeys without prompting a normal immune response, report Shyh-Ching Lo and his colleagues at the Armed Forces Institute of Pathology in Washington, D.C., and the National Institutes of Health in Bethesda, Md. Whether it plays a role in AIDS remains unclear, Lo says. However, because the mycoplasma appears to exist in such a high percentage of AIDS patients, and because many common antibiotics kill it in vitro, diagnosing and treating this infection may prove clinically important, he says. The researchers detail their findings in two articles in the November AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE.

In the September issue of the same journal, Lo's group reported detecting the mycoplasma in postmortem tissues from people without AIDS. Although many organs from those patients showed severe damage, the immune response appeared scant, Lo says.

Simpler than bacteria but more complex than viruses, mycoplasmas are the smallest known organisms that can live without a host (SN: 9/20/86, p.184). Several species cause pneumonia, kidney stones and premature labor. But until the advent of DNA probes and gene amplification techniques, mycoplasmas largely resisted study or diagnosis.

When Lo's team first isolated the organism's DNA from a Kaposi's sarcoma lesion of an AIDS victim, they thought it might be a large virus and named it VLIA, for virus-like infectious agent. They went on to detect the DNA in the spleen, liver, blood, brain and other organs of people who had died of AIDS and in the blood of 12 of 23 living AIDS patients, but found no sign of it in blood from 22 healthy donors. Later, however, Lo's lab received tissue from six people who had died one to seven weeks after the onset of flu-like symptoms. Microscopic tissue examination showed no signs of infection by bacteria, fungi, viruses or other parasites, but DNA probes and antibodies revealed the so-called VLIA.

Many fundamental questions remain for further research, Lo says. The researchers do not know how the mycoplasma sidesteps the immune system, or how it might relate to AIDS. Many people with AIDS show the same widespread organ damage and faulty immune response that M. incognitus can cause, Lo says, but no one knows how much of that damage results directly from the mycoplasma.

Researchers "should approach with caution" the question of whether Lo's group has truly found a new species of mycoplasma, says Joseph G. Tully, chief of the mycoplasma section of the National Institute of Allergy and Infectious Diseases. Nevertheless, he says, Lo's findings highlight the importance of mycoplasmas in human disease. "It's some very new information that may be very important down the road."