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Fusion of CD4+ cells by HIV-1 envelope proteins (Env) is a mechanism of virus spread and cell damage. Production of antibodies able to influence cell-cell fusion in vivo may affect the course of the infection. The effect of sera from 49 HIV-1-positive patients was tested on an in vitro fusion assay using Env-expressing and normal Jurkat T cells labelled with DiI and DiO dyes, and flow cytometry for quantification of cell-cell fusion. Sera varied in their activity on fusion: 69?4 % inhibited, 24?5 % had no effect and 6?1 % enhanced cell fusion. Fusion activity correlated positively with the CD4 + T-cell count and inversely with the viral load. Removal of IgG or IgM from sera reduced or eliminated inhibition and enhancing activities, respectively. Antibodies with inhibitory activity predominate in early and intermediate stages of infection, whereas loss of inhibition or enhancement of fusion correlates with progression to AIDS.Human immunodeficiency virus type 1 (HIV-1) frequently induces cell-cell fusion with syncytia formation in cultures of CD4 + T cells. Syncytia formation result from the interaction between infected cells expressing the virus envelope glycoprotein (Env) on their surface and neighbouring uninfected CD4+ cells (Lifson et al., 1986;Sodroski et al., 1986). Cell-cell fusion may have an important pathogenic role in vivo. HIV-1-infected giant multinucleated cells are frequently detected in the lymph nodes of asymptomatic and AIDS patients, and have been proposed as virus reservoirs (Budka 1986; Frankel et al., 1996;Koenig et al., 1986). Syncytium-inducing viruses (usually requiring CXCR4 as a co-receptor) associate with an increased rate of CD4 + T-lymphocyte depletion in patients and progression to AIDS (Blaak et al., 2000; Connor et al., 1993;Miedema et al., 1994). Peptides that interfere with virus-cell fusion decrease viral loads in humans (Kilby et al., 1998;Lazzarin et al., 2003). Furthermore, the membrane fusing ability of Env from a simian-human immunodeficiency virus chimera was determinant for CD4 + T-cell depletion in macaques (Etemad-Moghadam et al., 2001). Cell fusion is a significant cause of cell death in vitro, mainly by apoptosis triggered by aberrant initiation of mitosis (Castedo et al., 2002; Ferri et al., 2000;Laurent-Crawford et al., 1991). The magnitude of CD4 + cell-cell fusion events can be significant in lymphoid tissues, where there is close contact between cells (Amendola et al., 1996). On the other hand, cell-to-cell HIV-1 transmission without formation of syncytia, likely involving localized fusion events at cell contact points was proposed as a mechanism of transmission between individuals, and an important route of viral spread (Gupta et al., 1989;Phillips, 1994;Sato et al., 1992). Recently, it was shown that virus strains highly efficient in cell-to-cell transmission and with a syncitium-inducing phenotype are selected in an in vitro model of the rapid T-cell turnover known to occur during HIV-1 infection (Gummurulu et al., 2000).Inhibition of pathogenic cell-cell ...

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IntroductionWithin the first weeks of human immunodeficiency virus (HIV) infection, virus replication reaches systemic circulation. Despite the critical, causal role of virus replication in determining transmissibility and kinetics of disease progression, there is limited understanding of the conditions required to transform a small localized transmitted founder population into a large and heterogeneous systemic infection.MethodsCynomolgus and rhesus macaques were infected with simian immunodeficiency virus (SIV) and followed longitudinally. Plasma levels of SIV were monitored using qRT-PCR. Bacterial genomic DNA in plasma was characterized and quantified longitudinally using 16S ribosomal deep sequencing and qPCR. ELISA-based assays were used to monitor intestinal permeability (IFABP) and perturbation of bacteria-specific host factors (sCD14 and EndoCab). Flow cytometry was used to track peripheral blood lymphocyte populations. In vitro assays were performed by exposing freshly isolated peripheral blood mononuclear cells to bacterial lysate prepared from major translocators. Effects of bacterial lysate on CD4+ T cell activation and CD8+ T cell cytotoxicity were measured using flow cytometry. Statistical significance was calculated using ANOVA or Wilcoxon signed-rank testing.ResultsPrior to the peak of viremia, we observed a transient high-level influx of microbial genomic DNA into peripheral blood. This microbial translocation was accompanied by perturbation of bacteria-specific host factors in plasma, as well as expansion of the CD4+CCR5+ T cell compartment. Exposure of freshly isolated peripheral blood mononuclear cells to lysate prepared from major translocating taxa revealed differential taxa-specific effects on the CD4+CCR5+ T cell compartment and cytotoxic granule expression within CD8+ T cells.ConclusionsAltogether, our data identify the influx of microbial products into blood during hyperacute SIV infection as a candidate modifier of early interactions between the antiviral host response and nascent HIV infection. Over the next few months, we will explore the effect of inducing microbial translocation during SIV infection, with particular interest on microbial reactivity within the CD4+CCR5+ target cell compartment.

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