CD8+ cell-mediated immune responses: relation to disease resistance and susceptibility in lentivirus-infected primates

In vitro replication of SIVcpz is suppressed by beta-chemokines and CD8+ T cells but not by natural killer cells of infected chimpanzees

Unlike humans, chimpanzees are relatively resistant to AIDS after infection with HIV-1 or simian immunodeficiency virus of chimpanzee (SIVcpz). We hypothesized that resistance to disease progression is associated with efficient suppression of virus replication possibly by beta-chemokines secreted by CD8+ lymphocytes and especially natural killer (NK) cells. In vitro suppression of virus replication can be easily studied in SIVcpz-infected chimpanzees because they produce high infectious virus titers in their peripheral blood. A study was undertaken to assess the sensitivity of SIVcpz to beta-chemokines in vitro and to investigate the role of endogenous beta-chemokines in relation to the in vitro capacity of CD8+ lymphocytes and NK cells of chimpanzees to suppress SIVcpz replication. Our results show that SIVcpz uses CCR5 as a coreceptor to gain cell entry and is sensitive to recombinant beta-chemokines in vitro. Here we report that despite their potent capacity to produce RANTES, NK cells of infected chimpanzees do not suppress SIVcpz replication in vitro, in contrast to CD8+ lymphocytes. We also show that endogenous beta-chemokines are not the predominant factors mediating in vitro suppression.

High levels of viral replication during primary simian immunodeficiency virus SIVagm infection are rapidly and strongly controlled in African green monkeys

In contrast to pathogenic human immunodeficiency virus and simian immunodeficiency virus (SIV) infections, chronic SIVagm infections in African green monkeys (AGMs) are characterized by persistently low peripheral and tissue viral loads that correlate with the lack of disease observed in these animals. We report here data on the dynamics of acute SIVagm infection in AGMs that exhibit remarkable similarities with viral replication patterns observed in peripheral blood during the first 2 weeks of pathogenic SIVmac infections. Plasma viremia was evident at day 3 postinfection (p.i.) in AGMs, and rapid viral replication led by days 7 to 10 to peak viremias characterized by high levels of antigenemia (1.2 to 5 ng of p27/ml of plasma), peripheral DNA viral load (10(4) to 10(5) DNA copies/10(6) peripheral blood mononuclear cells [PBMC]), and plasma RNA viral load (2 x 10(6) to 2 x 10(8) RNA copies/ml). The lymph node (LN) RNA and DNA viral load patterns were similar to those in blood, with peaks observed between day 7 and day 14. These values in LNs (ranging from 3 x 10(5) to 3 x 10(6) RNA copies/10(6) LN cell [LNC] and 10(3) to 10(4) DNA copies/10(6) LNC) were at no time point higher than those observed in the blood. Both in LNs and in blood, rapid and significant decreases were observed in all infected animals after this peak of viral replication. Within 3 to 4 weeks p. i., antigenemia was no longer detectable and peripheral viral loads decreased to values similar to those characteristic of the chronic phase of infection (10(2) to 10(3) DNA copies/10(6) PBMC and 2 x 10(3) to 2 x 10(5) RNA copies/ml of plasma). In LNs, viral loads declined to 5 x 10(1) to 10(3) DNA copies and 10(4) to 3 x 10(5) RNA copies per 10(6) LNC at day 28 p.i. and continued to decrease until day 84 p.i. (<10 to 3 x 10(4) RNA copies/10(6) LNC). Despite extensive viremia during primary infection, neither follicular hyperplasia nor CD8(+) cell infiltration into LN germinal centers was detected. Altogether, these results indicate that the nonpathogenic outcome of SIVagm infection in its natural host is associated with a rapidly induced control of viral replication in response to SIVagm infection, rather than with a poorly replicating virus or a constitutive host genetic resistance to virus replication.

The decreased replicative capacity of simian immunodeficiency virus SIVmac239Delta(nef) is manifest in cultures of immature dendritic cellsand T cells

Transmission of simian immunodeficiency virus SIVmac239Delta(nef) (Delta(nef)) to macaques results in attenuated replication of the virus in most animals and ultimately induces protection against challenge with some pathogenic, wild-type SIV strains. It has been difficult, however, to identify a culture system in which the replication of Delta(nef) is severely reduced relative to that of the wild type. We have utilized a primary culture system consisting of blood-derived dendritic cells (DCs) and autologous T cells. When the DCs were fully differentiated or mature, the DC-CD4(+) T-cell mixtures supported replication of both the parental SIV strain, 239 (the wild type), and its mutant with nef deleted (Delta(nef)), irrespective of virus dose and the cell type introducing the virus to the coculture. In contrast, when immature DCs were exposed to Delta(nef) and cocultured with T cells, virus replication was significantly lower than that of the wild type. Activation of the cultures with a superantigen allowed both Delta(nef) and the wild type to replicate comparably in immature DC-T-cell cultures. Immature DCs, which, it has been hypothesized, capture and transmit SIV in vivo, are deficient in supporting replication of Delta(nef) in vitro and may contribute to the reduced pathogenicity of Delta(nef) in vivo.