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To use SIVmac-infected Chinese-origin rhesus macaques (Ch Rh) to characterize the immunopathology of the long term non-progressor (LTNP) state. The key questions addressed were whether or not LTNP experience an early and rapid loss of mucosal CD4 T cells during the acute infection and the mechanisms by which they maintain the LTNP state.Ch Rh were infected with SIVmac239. Polychromatic flow cytometry was used to analyze T lymphocyte subsets from blood, lymph nodes and gut tissues during SIV infection. Plasma viral loads were monitored by bDNA assay. Two LTNP were treated with anti-CD8 antibody to deplete CD8 cells in vivo.Thirty-one percent (5/16) of SIVmac239-infected ChRh having low viral loads for as long as 6 years were LTNP. Both LTNP and progressors had similar levels of gut memory CD4/CCR5 T cells (target cells) before infection and there was an early and profound depletion of target cells in both groups. LTNP were distinguished by gradual restoration of mucosal target cells which was evident by 6 months post infection. In vivo CD8 depletion in two LTNP induced AIDS in one LTNP (V542) post anti-CD8 treatment and the other (AJ07) remained healthy after a transient spike in viremia.Early destruction of target cells was equivalent in LTNP and progressors and did not predict clinical outcome. Restoration of target cells in the gut is associated with long term non-progression. CD8 T cells may play a critical role on maintaining the LTNP state.