Abstract
We have reported previously the enhancement of the infectivity of human immunodeficiency virus type 1 (HIV-1) by liposomes composed of the cationic lipid N-[2,3-(dioleyloxy) propyl]-N,N,N-trimethylammonium chloride (DOTMA). To determine the mechanism by which this process occurs, we have investigated the role of CD4, serum concentration and liposome-cell interactions in the DOTMA-mediated stimulation of HIV-1 infection of A3.01 cells. Serum alone significantly inhibited the binding and infectivity of HIV-1, but DOTMA-mediated enhancement of infectivity was more pronounced in the presence of serum than in its absence. HIV-1 binding to cells was increased in the presence of DOTMA liposomes, DEAE-dextran and polybrene, all of which also enhanced infectivity to a similar extent at comparable concentrations. Fluorescence dequenching measurements indicated that DOTMA liposomes fused with HIV-1, but not with cell membranes, in the presence of serum. The enhancing effect of DOTMA liposomes on HIV-1 infectivity was CD4-dependent, and appeared to involve virus-liposome fusion and liposome binding to the cell surface. DOTMA liposomes did not mediate infection of the CD4-K562 and Raji cell lines.
Highlights
Human immunodeficiency virus type 1 (HIV-1) is known to use the CD4 protein as its cellular receptor, and to infect CD4 ÷ T lymphocytes (Dalgleish et al, 1984; Klatzmann et al, 1984; McDougal et al, 1986) and other CD4-bearing cells, such as monocytes and macrophages (Gartner et al, 1986; Ho et al, 1986; Nicholson et al, 1986), Langerhans cells (Tschachler et al, 1987) and human peripheral blood dendritic cells (Patterson & Knight, 1987)
Fusion of HIV-1 with DOTMA liposomes was dependent on the reaction conditions (Table 1), being faster in NaC1/TES than in RPMI in the absence of serum; the pH of each solution was 7.5
The initial rate o f fusion in RPMI was reduced by roughly one-third in the presence of 1% or 10% foetal bovine serum (FBS), serum had less effect on the extent of lipid mixing measured after 2.5 min
Summary
Human immunodeficiency virus type 1 (HIV-1) is known to use the CD4 protein as its cellular receptor, and to infect CD4 ÷ T lymphocytes (Dalgleish et al, 1984; Klatzmann et al, 1984; McDougal et al, 1986) and other CD4-bearing cells, such as monocytes and macrophages (Gartner et al, 1986; Ho et al, 1986; Nicholson et al, 1986), Langerhans cells (Tschachler et al, 1987) and human peripheral blood dendritic cells (Patterson & Knight, 1987). That infection is not prevented by anti-CD4 antibodies or neutralizing doses of recombinant soluble CD4 (rsCD4) (Clapham et al, 1989; Weber et al, 1989; Weiss et al, 1989) suggests that receptors other than CD4 are responsible for the susceptibility of these cells to HIV. There are two essential steps in HIV-1 entry into the cell: binding of virus to the cell membrane, and fusion of viral and cell membranes Both steps are mediated by two viral envelope proteins, a trans-membrane glycoprotein, gp, thought to mediate the fusion step, and a glycoprotein, gpl, attached non-covalently to gp, responsible for binding to CD4 (Lifson et al, 1986a; Sodroski et al, 1986; Kowalski et al, 1987). Binding of rsCD4 or the purified V1 domain of sCD4 to gpl on HIV-1 virions results in dissociation of gp 120 from its complex with gp (Moore et al, 1990); shedding of gpl may represent the initial stage in virus-cell fusion
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