Human immunodeficiency virus 1 (HIV-1) envelope-dependent cell–cell fusion modulation by HIV-positive sera is related to disease progression

Abstract

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 ...

Constrained peptide models from phage display libraries highlighting the cognate epitope-specific potential of the anti-HIV-1 mAb 2F5

“…The results of those immunizations were basically negative despite the presentation of the ELDKWAS (or some longer sequence) peptide on various vectors and the inclusion of a fusion peptide sequence [45] and lipids [46] as parts of the viral structures to optimize the 2F5 antigenic function (see [37] for exhaustive critical analysis of this item). Using a cell-cell fusion system, which was proven to be highly sensitive to inhibitors in our previous experiments [31][32][33][34][35] against 2F5 in this study, we found that mouse antiserum to the both the linear and constrained peptides did not affect fusion while the rabbit antiserum to the linear but not to the constrained peptide decreased fusion by approximately 50% and to 20% at 1:10 and 1:100 dilutions, respectively. Inhibition by mAb 2F5 was not observed in the presence of the 15-mer ELDKWAS-containing peptide competitor of the epitope (Fig.…”

“…The cell-cell fusion protocol developed by Huerta et al [31] and subsequently extensively employed by Huerta et al [32], López-Balderas et al [33], Huerta et al [34], Rivera-Toledo et al [35] was used in these experiments to test the anti-mimotope serum antibodies. The protocol involves labeling fusion partner cells with the fluorescent carbocyanines DiI and DiO (Molecular Probes).…”

“…The fusogenic HXBc2 cell line was grown in the presence of 1 g/ml tetracycline and selection antibiotics (200 g/ml G418 and 200 g/ml hygromycin) as described previously [31][32][33][34][35][36]. Expression of the gp120/gp41 viral env protein was induced by removing tetracycline by washing the cells with PBS and incubating in RPMI-10 with selection antibiotics for 3 days.…”

HIV-Envelope–Dependent Cell-Cell Fusion: Quantitative Studies

“…We explored the effect of sera from HIV-infected individuals on the fusion of Env + and CD4 + Jurkat cells [103]. Most (69%) of the sera from a sampling of 49 HIV-positive individuals inhibited fusion to some extent; 24.5% had no effect and 6.1% enhanced fusion.…”

An Inducible Cell-Cell Fusion System with Integrated Ability to Measure the Efficiency and Specificity of HIV-1 Entry Inhibitors

“…Cell-cell fusion assays are attractive tools for identifying potent inhibitors of HIV-1 Env function. Such assays mimic the entry steps of HIV-1 into cells, and can measure membrane-fusing activity, as well as its inhibition, with high sensitivity [43], [44], [45], [46], [47], [48], [49], [50], [51], [52]. The assay also simulates the multiple Env-receptor interactions that occur during direct transmission of the virus from one cell to another, and offers a unique system to study and potentially inhibit this mode of transmission [53], [54], [55].…”