The immune system has a number of ways of dealing with HIV-infected cells:
This second function is largely performed by a type of immune cell called CD8+ cells. These cells can produce antiviral chemicals that are non-toxic to healthy cells and have the potential to clear HIV from infected cells. Although much research is underway to identify the chemicals produced by CD8+ cells, so far no research team has been able to find out what they are. However, at least one research team suspects that by releasing these antiviral compounds, CD8+ cells may also play a role in preventing HIV infection in some people exposed to the virus.
Researchers at the University of California at San Francisco (UCSF) have been working for more than a decade to try to identify and understand how the naturally produced antiviral substances work. In one study, they found that the immune system is usually able to maintain production of the antiviral compounds for the first 10 years after a person becomes HIV positive. In general, by the time HIV positive people develop AIDS-related symptoms and levels of CD4+ cells fall, production of antiviral substances has also decreased.
In their latest study, the UCSF researchers studied 20 healthy subjects who had been HIV positive for at least 10 years. The purpose of the study was to find out if there was any link between production of natural antiviral substances by CD8+ cells and CD4+ cell counts.
Study details
Researchers recruited 20 male subjects who were free from symptoms of AIDS. Eighteen of the 20 subjects had never used anti-HIV therapy nor was anyone currently receiving such treatment. Technicians analysed blood samples from subjects for CD4+ cell levels and the ability of CD8+ cells to produce antiviral substances.
Results
In general, researchers found that subjects could be divided into two groups:
Key findings from the study were as follows:
In this study, researchers found that the immune systems of healthy HIV positive subjects who had fewer than 300 CD4+ cells were significantly less able to suppress HIV than similar subjects who had more than 300 CD4+ cells. These findings provide, according to the research team, "immunologically based evidence" that supports current treatment guidelines. The findings may also be another factor to weigh when making decisions about the timing of anti-HIV therapy.
REFERENCES
1. Guidotti LG and Chisari FV. Noncytolytic control of viral infections by the innate and adaptive immune response. Annual Review of Immunology 2001;19:65-91.
2. Locher CP, Witt SA, Levy JA. The nuclear factor kappa B and Spl binding sites do not appear to be involved in virus suppression by CD8 T lymphocytes. AIDS 2001;15(18):2455-2457.
3. Stranford SA, Skurnick J, Louria D et al. Lack of infection in HIV-exposed individuals is associated with a strong CD8(+) cell noncytotoxic anti-HIV response. Proceedings of the National Academy of Sciences USA 1999;96(3):1030-1035.
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