HIV Finds a New Home in the Brain

By: Ian Cohn
Edited by: Arianna Winchester
HIV/AIDS, first discovered about 30 years ago, still remains one of the top ten causes of death in the world, according to the World Health Organization. HIV, or Human Immunodeficiency Virus, is a contagious virus that is usually understood to impair immune function in those infected with it. The virus attacks a type of immune cell called T cells: an important subset of white blood cells responsible for fending off foreign invaders in our bodies. The virus replicates and grows in T cells, but the virus cannot reside in a single cell for too long. Once the virus has co-opted a host T cell and drained it of its cellular material, it discards the used T cell and moves on to destroy other healthy white blood cells. This is why those who are HIV-positive often are more vulnerable to sickness; they have less healthy white blood cells to stave off infection. This is also how some patients reach the final stage of HIV infection, known as AIDS, or Acquired Immunodeficiency Syndrome. A patient is said to have AIDS only after the onset of HIV infection; the term AIDS functions as a definition for the extremely low T cell count and advanced infections caused by the ineffectiveness of their weakened immune system. While there are therapies for those suffering from HIV/AIDS, there currently are no cures or vaccines for the disease. Still, due to its high rate of morbidity worldwide, in the 30 years since the discovery of HIV/AIDS, a lot of research in the field of Infectious Diseases has focused on this specific virus.
[caption id="attachment_1122" align="aligncenter" width="610"](HIV (green), leaving a human T cell via Wikipedia)[/caption]As described above, HIV/AIDS causes a decrease in immune function in its human hosts. For many years this was thought to be its only effect. However, recent research from the University of North Carolina at Chapel Hill suggests that HIV may be able to act in new, more dangerous ways that cause problems that extend past the immune system. The study, published this March, suggests that HIV can migrate to the central nervous system (CNS)—the term for the brain and spinal cord—and can cause a whole new set of problems for its human host. In a process called compartmentalization, the HIV virus “sets up shop” in the human brain as early as four months after infection.
Once it is in the brain, the virus can mutate independently from the viruses circulating in the systemic (non-brain) blood. While it has been known for a long time that HIV can cause defects in a patient’s central nervous system, the fact that it has now been proven to compartmentalize in the brain and mutate into an independent population is uniquely troubling, in that it proves that the virus can specifically infect the brain rather than merely circulate through it in the bloodstream. Since the patient has two differently mutated versions of HIV in his/her body, both of which are capable of inflicting serious damage on the body, we now realize the disease is more intense than we thought, since the two “versions” of the virus seem to generate twice the amount of infectious material in one person.
HIV’s specific infection of the brain brings more trouble for researchers who remain optimistic that we are close to a cure for HIV/AIDS. Drug treatment for CNS disorders requires a special ability to cross the blood/brain barrier, the spinal fluid separating the bloodstream from the CNS. The chemical make-up of most drugs means that they cannot diffuse across this fluid, so many drugs that may work in the rest of the body would not be able to treat brain-infecting HIV. New drugs must be developed to be able to cross this biological barrier in patients, which is no easy task. In addition, the fact that HIV inside humans can differentiate into two distinct populations (the population in the brain and the population in the rest of the body) adds further difficulty to the problem. Should these two populations be targeted independently or together? All of these implications and findings continue to fuel the fire pushing for HIV/AIDS research. While much work has been done and is being done on the disease, there is clearly a lot left to do.