Researchers Find AIDS Virus Hides In Lymph Nodes
WASHINGTON (AP) _ The AIDS virus is active for years in lymph nodes where it forms reservoirs of infection that eventually spill over with lethal effect, according to research published today.
The discovery suggests earlier treatment is essential for longer life.
Two groups of researchers reported in the journal Nature that after an AIDS virus infection starts, the virus congregates in lymphoid organs, such as the tonsils, adenoids and lymph nodes. There, the virus infects key blood cells and kill cells that filter out viruses.
After the filter cells are destroyed, infected blood cells and virus particles cascade into the blood for the final, lethal stage of the disease, the researchers found.
These findings, they said, show that the AIDS virus is never idle, and that drug therapy needs to start from the moment of diagnosis.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and a co-author of one of the studies, said the discovery answers one of the key mysteries about the AIDS virus disease.
Fauci said many patients infected with HIV, the virus that causes AIDS, experience an initial bloom of virus in their blood. Virus particles then become rare in blood tests and patients may live without symptoms for a decade. Eventually, there is another bloom of virus, usually followed by death from some opportunistic infection.
″Since there was little virus in the blood, it was a puzzle why this process inevitably progressed and occurred,″ Fauci said. ″The bottom line of the study is that this virus is present in the lymph nodes ... and it is actively replicating ... even when there is little or no virus activity detected in the blood.″
In effect, said Fauci, the period that doctors call the latent stage of the HIV is not latent at all. The virus is thriving in the lymph nodes and insidiously eroding the body’s immune system.
A second study, co-authored by Dr. Ashley T. Haase of the University of Minnesota, confirmed the high level of HIV in lymphoid tissue during the so- called latent period of disease. He said the virus was actively infecting lymphocytes, called CD4 T-cells, that are in the lymph nodes.
CD4 T cells, the ″helper T-cells″ of the immune system, are the principal targets of HIV, or human immunodeficiency virus. The level of these T-cells is used as a key marker in the progress of HIV infection.
Haase said he and his colleagues found ″an extraordinarily large number″ of infected CD4 T-cells in the lymph tissue. He said only about a tenth of these cells, however, were capable of growing new virus. Instead, said Haase, these cells seem to act as ″a reservoir of infection.″
″I estimate that perhaps as many as 100 billion cells are latently infected at any given time and perhaps a billion cells are productively infected,″ he said. ″I liken it to a constantly erupting volcano ... with latently infected cells feeding the productively infected ones.″
Productively infected T-cells are able to make new virus. Some of the latently infected cells can never become productive, but others may be ″turned on″ to make the virus.
Dr. Howard M. Temin of the University of Wisconsin-Madison, and Dr. Dani P. Bolognesi of Duke University, both noted AIDS and virus researchers, said the findings were ″highly thought-provoking″ and could influence the design of vaccines for HIV.
Earlier studies detected HIV in the lymph nodes, but the new work went a step further. Fauci and his co-researchers tested both blood and lymphoid tissue taken from the same patients at the same time. They found about 10 times more virus in the lymph organs than in the blood samples.
Both Fauci and Haase said a key to controlling HIV will be to find drugs that can be taken shortly after infection and before the virus establishes infection reservoirs in the lymph nodes.
Current AIDS drugs are toxic and can trigger viral resistance. As a result, the drugs are given for limited periods and are not prescribed until the CD4 T-cell counts have dropped to a fraction of normal.
″When we get those drugs that are non-toxic and do not readily induce resistance, then we would treat someone early and aggressively,″ Fauci said.