Interleukin 18 stimulates HIV type 1 in monocytic cells - PubMed (original) (raw)

Interleukin 18 stimulates HIV type 1 in monocytic cells

L Shapiro et al. Proc Natl Acad Sci U S A. 1998.

Abstract

The cytokine interleukin (IL) 18 (formerly interferon gamma-inducing factor) induces the T helper type 1 response. In the present studies, IL-18 increased HIV type 1 (HIV-1) production from 5- to 30-fold in the chronically infected U1 monocytic cell line. Inhibition of tumor necrosis factor (TNF) activity by the addition of TNF-binding protein reduced IL-18-stimulated HIV-1 production by 48%. In the same cultures, IL-18-induced IL-8 was inhibited by 96%. Also, a neutralizing anti-IL-6 mAb reduced IL-18-induced HIV-1 by 63%. Stimulation of U1 cells with IL-18 resulted in increased production of IL-6, and exogenous IL-6 added to U1 cells increased HIV-1 production 4-fold over control. A specific inhibitor of the p38 mitogen-activated protein kinase reduced IL-18-induced HIV-1 by 73%, and a 50% inhibition was observed at 0.05 microM. In the same cultures, IL-8 was inhibited by 87%. By gel-shift and supershift analyses, increased binding activity of the transcription factor NF-kappaB was measured in nuclear extracts from U1 cells 1 h after exposure to IL-18. These results demonstrate induction of HIV-1 by IL-18 in a monocyte target associated with an intermediate role for TNF and IL-6, activation of p38 mitogen-activated protein kinase, and nuclear translocation of NF-kappaB.

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Figures

Figure 1

Figure 1

Mature, but not precursor, form of IL-18 stimulates p24 antigen production in U1 cells: effect of TNFbp. In five separate experiments, U1 cells were incubated in medium alone (control) or with increasing concentrations of precursor (solid bars) or mature IL-18 (open bars) as indicated. After 48 h, p24 antigen was measured. ∗, P < 0.05 compared with medium alone; ∗∗, P < 0.001 compared with medium alone. Cells were also cultured with mature IL-18 in the presence of 10 μg/ml TNFbp added 1 h before IL-18 (hatched bars). •, P < 0.05 compared with IL-18 alone; ••, P < 0.001 compared with IL-18 alone.

Figure 2

Figure 2

Effect of TNFbp on IL-18-induced IL-8. In the same cultures shown in Fig. 1, cells were incubated with mature IL-18 at the concentrations shown (open bars) in the presence or absence of 10 μg/ml TNFbp added 1 h before IL-18 (hatched bars). IL-8 was measured as described in Materials and Methods. ∗, P < 0.05 compared with medium alone; ∗∗, P < 0.001 compared with medium alone; •, P < 0.05 compared with IL-18 alone; ••, P < 0.001 compared with IL-18 alone.

Figure 3

Figure 3

Effect of neutralizing anti-IL-6 antibody on IL-18-induced p24 antigen in U1 cells. (A) In three separate experiments, cells were incubated with medium alone (control), with 1.0 nM IL-18, or with IL-18 in the presence of anti-IL-6 mAb (1–10 μg/ml) added 1 h before IL-18. p24 antigen was measured after 48 h of incubation. (B) In the same cultures shown in A, IL-8 was measured. No significant effect of anti-IL-6 (1–10 μg/ml) was observed for IL-18-induction of IL-8. ∗, P < 0.05 compared with cells stimulated with IL-18 in the absence of anti-IL-6 mAb.

Figure 4

Figure 4

Stimulation of p24 antigen by IL-6. In six separate experiments, U1 cells were stimulated with recombinant human IL-6 at the concentrations indicated. After 48 h, p24 antigen was assayed in the cultures. The baseline (medium alone) value for each experiment was set at 100% and the mean percentage increase ± SEM is shown for the different concentrations of IL-6. ∗∗, P < 0.01; ∗∗∗, P < 0.001 compared with unstimulated cultures.

Figure 5

Figure 5

Effect of p38 MAPK inhibitor on IL-18-induced p24 antigen and IL-8 in U1 cells. (A) Cells were cultured in polypropylene tubes with IL-18 (1.0 nM) alone or in the presence of the p38 MAPK inhibitor at the concentrations indicated. Production of p24 antigen was measured after 24 h. For each experiment, the baseline (unstimulated) level was subtracted from each condition, and the level of stimulation with IL-18 was set at 100%. The results are expressed as percentage change (±SEM) compared with IL-18 only. (B) In the same cultures shown in A, IL-8 was measured as described in Materials and Methods. ∗, P < 0.01 compared with IL-18 alone (100%); ∗∗, P < 0.001 compared with IL-18 alone (100%). n = 3 separate experiments.

Figure 6

Figure 6

Nuclear translocation of NF-κB in IL-18-stimulated U1 cells. U1 cells (5.0 × 106 per ml) were cultured in medium for 1 h in the absence (control, lanes 1–3) or presence (5.0 nM, lanes 4–6) of IL-18. Nuclear proteins were isolated and hybridized to an oligonucleotide probe containing the NF-κB-binding region as described in Materials and Methods (the unbound probe is not shown). Lanes: 1 and 4, gel shift for control cells and cells exposed to IL-18, respectively; 2 and 5, a supershift by using anti-p50 subunit antibody for control and stimulated cells, respectively; 3 and 6, incubation of nuclear proteins with radiolabeled probe in the presence of excess unlabeled probe.

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