Animal models of AIDS provide good support for pathophysiologic studies that aim to progress in the understanding of the virus-host relationship. Immediately after experimental inoculation with pathogenic simian immunodeficiency virus (SIV), macaques develop an acute infection controlled by a strong immune response, which is followed by a chronic infection leading to simian AIDS within 1-4 years. During HIV/SIV infection, both CD8+ and CD4+ T cells display phenotypical and functional signs of excessive activation and anergy [1]. In HIV-infected individuals, a decreased proportion of peripheral T cells expressing costimulatory molecules such as CD28 on CD8+ T cells [2-5] and CD7 on CD4+ T cells has been reported [6, 7]. In this study, we focused on the last stages of SIV infection by studying the evolution of the T-cell population in a group of 10 macaques infected intravenously with 4 median animal infectious doses of SIVmac251 virus during 4 years.

First, the percentages of CD28+ and CD7+ T cells were measured in the blood of 10 non-infected cynomolgus macaques. Similar to human peripheral blood T cells, CD28 and CD7 molecules were found to be expressed on 85 and 86% of CD4+ T cells, respectively, and on 57 and 66% of CD8+ T cells, respectively.