Researchers from the Johns Hopkins Bloomberg School of Public Health and the Johns Hopkins School of Medicine used positron emission tomography (PET) scans to identify sites of replicating HIV in the lymphatic system of people recently infected with the virus. PET scan imaging is typically used to detect tumors. The researchers believe PET scans could lead to greater understanding of HIV disease and new methods for treating the infection. Their findings are published in the September 20, 2003, edition of The Lancet.
According to the study, the PET scans recorded activation of the lymph nodes, which are involved in the body's immune response. Activation was most notable in lymph nodes in upper torso and neck areas of the body among participants recently infected with HIV. Nodes in the lower torso were involved to a lesser extent. Participants who were infected with HIV for a longer period and remained asymptomatic with low viral loads also had lymph node activation in the neck, upper torso and pelvic areas. The researchers observed a tight correlation between the viral replication and the lymph node activity on the PET signal.
Lead author Sujatha Iyengar, PhD, and David Schwartz, MD, PhD, senior investigator of the study, propose that PET scans could be used to locate the specific nodes where HIV is replicating and remove them or target them with radiation. "Although many systemic sites from which latent virus could be reactivated would be left, reactivation might not occur for months or years after removal of the active nodes, thereby allowing extended interruption of treatment for the disease. Despite the systemic nature of HIV infection, the sites of viral replication appear remarkably restricted to limited anatomic locations at any given time. This suggests microenvironmental niche selection in true Darwinian fashion," noted Dr. Schwartz, who is an associate professor with the School's Department of Molecular Microbiology and Immunology.
"Equally important for the future of this technology is the observation that immune responses to vaccines can be anatomically localized and measured in normal individuals," said Dr. Iyengar, who is a research associate with the Department of Molecular Microbiology and Immunology. "This could be invaluable in the evaluation of new vaccines and routes of administration."
For the study, the researchers used PET scans to examine 23 people who were HIV-positive, 12 of whom had recently been infected. The other 11 had been infected for a long period of time, but none of the participants had any signs of disease or illness. The researchers also scanned eight non-infected individuals as a control group. They were given influenza vaccine to stimulate lymph node activation.
"Anatomical loci of HIV-associated immune activation and association of viraemia" was written by Sujatha Iyengar, Bennett Chin, Joseph B. Margolick, Beulah P. Sabundayo and David Schwartz.
Funding for the study was provided by grants from the National Institutes of Health, the Center for AIDS Research and the Alternatives Research Development Fund.
News releases from the Johns Hopkins Bloomberg School of Public Health are available at http://www.jhsph.edu.
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