Background: The Nef protein of HIV-1 is suspected to play a role in the depletion of uninfected CD4+ lymphocytes that leads to AIDS. By contrast its effect on CD8+ cells, whose functions are also deregulated during HIV-1 infection, is presently unclear. Here we describe a number of derangements induced in vitro by Nef in CD8+ cells from HIV-1-infected patients.
Design: Peripheral lymphocytes from 16 HIV-1+ subjects and 9 uninfected individuals were cultivated on a Nef-transfected mouse fibroblast layer exposing the carboxyl-terminal region of the viral protein on cell membrane. The cultures were then measured for both apoptosis and proliferation by subdiploid DNA content and Ki67 expression, respectively, whereas the molecular analysis of purified CD8+ cells investigated the Fas-L mRNA levels in Nef-treated CTLs. In addition, we evaluated the Nef-induced variation in the extent of CD8+/HLA-DR+ subset, which includes non cytotoxic cells secreting T-cell antiviral factor (CAF) and a soluble factor inhibiting the HIV-1 replication.
Results: The viral protein induced in peripheral blood lymphocytes (PBL) a moderate tendency to proliferate, as measured by the increment of Ki67 antigen, particularly on the CD8+ subset of HIV-1 infected individuals (P < 0.05). This profile was particularly evident in cultures from patients with severe CD4+ lymphopenia and paralleled an apparent expansion of the CD8+/CD57+ suppressor cell subset. Molecular analysis of purified CD8+ cells revealed a defective expression of Fas-L mRNA in Nef-cultured CTLs, whereas the viral protein exerted a down modulatory effect on the CD8+/HLA-DR+ subset (P < 0.05), thus suggesting a potential inhibition of CAF.
Conclusions: These results support a potential role of Nef in the progression of HIV-1 infection as a number of cellular functions are affected in the CD8+ subset. In particular, the defective functions of CD8+ cells induced by the viral protein could contribute, at least partly, to the escape of HIV-1 from the immune control of these cells.