Measuring the number of CD4+ T cells in the blood is a convenient way for researchers to estimate the damage HIV is doing to the immune system, since blood samples are easily obtained. But the majority of the body's CD4+ T cells aren't in the blood. Rather they are found in the mucosal tissues, such as those lining the respiratory, gastrointestinal and genital tracts. Researchers have recently focused on studying the immune responses occurring specifically at these mucosal sites. They found something very interesting. In both animal models and humans, researchers observed a massive killing of CD4+ T cells at mucosal surfaces in the intestine, or gut, very early in the course of HIV infection. Recovery of these cell populations is slow after treatment has begun. Many organizations involved in developing AIDS vaccine candidates are therefore interested in studying recently HIV-infected individuals. IAVI is one group conducting this type of epidemiological study with recently HIV-infected volunteers at several centers in Africa. Another important implication from this research is the need for AIDS vaccine candidates that induce strong immune responses at mucosal tissues, especially those lining the intestine.
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