Mangabeys, Memory Cells, and SSV Infection of humans with HIV and rhesus macaques with the simian counterpart, SIV, is eventually fatal if left untreated. Some species of monkeys, however, are able to be infected with SIV and not progress to AIDS, even in the face of high viral loads. These so-called "natural hosts," which include sooty mangabeys and African green monkeys, are of interest to researchers because they may provide insight into the ways in which the immune system can combat HIV. Because high viral loads are seen in the SIV-infected sooty mangabeys, but relatively little depletion of CD4~+ T cells is seen as compared to SIV-infected rhesus macaques, Paiardini et at. sought to determine whether differences in the CD4~+ T cell subsets might result in the different outcomes of SIV infection in these animals. The authors found that in contrast to rhesus macaques, activated CD4~+ central memory T cells from sooty mangabeys did not up-regulate the chemokine receptor CCR5, the co-receptor required for SIV infection. These CCR5~(low) central memory CD4~+ T cells were less susceptible to SIV infection than central memory CD4~+ T cells from rhesus macaques.
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