Circulating levels of IL-18 in adult and paediatric... : AIDS (original) (raw)
IL-18, formerly IFN-γ-inducing factor, is produced by several cell types, including activated mononuclear cells and epidermal cells [1,2]. Furthermore, IL-18 induces the production of IFN-γ from natural killer cells [3,4], and along with IL-12 has a synergistic effect on the induction of IFN-γ[4,5]. Recently, Shapiro et al. [6] suggested a role for IL-18 in HIV-1 pathogenesis because of the ability IL-18 shares with the proinflammatory cytokines IL-1 and TNF to stimulate HIV-1 production in the chronically infected U1 monocytic cell line. To confirm these in-vitro results, and to gain further insight into the role of IL-18, we evaluated circulating levels of IL-18 in adult and paediatric HIV-1-infected patients at various phases of the disease.
Thirty-seven adult patients (28 male, nine female; mean age 35.8 ± 7.1 years) with HIV-1 infection, seven HIV-1-infected children (three male, four female; mean age 4.7 ± 5.3 years), and four HIV-1-seronegative children (three male, one female; mean age 2.5 ± 2.1 years), born to HIV-1-infected mothers, were included in the study. The patients were clinically classified according to the 1993 revised criteria from the Centers for Disease Control and Prevention [7]. Among adult patients, 13 were asymptomatic (category A), eight were symptomatic with no AIDS-defining events (category B), and 16 were AIDS patients (category C), whereas in paediatric patients, four were symptomatic (category B), and three were AIDS patients (category C). CD4 cell counts and plasma virus loads for the paediatric population were 655.0 ± 190.0 cells/μl and 15 440 ± 4850 copies/ml, respectively. CD4 cell counts for the three groups of adult HIV-1-infected patients, respectively, were 580.0 ± 44.0 cells/μl (category A), 310.0 ± 60.0 cells/μl (category B), and 103.0 ± 35.0 cells/μl (category C). Plasma virus loads were available for 10 asymptomatic patients (mean values 1250.0 ± 361.0 copies/ml), seven symptomatic patients (mean values 25 782.0 ± 5576 copies/ml), and 16 AIDS patients (mean values 177 543 ± 96,745 copies/ml). All adult and paediatric patients were given antiretroviral drug therapy, including nucleoside or non-nucleoside reverse transcriptase inhibitors, or protease inhibitors during the period of the study, but they were not receiving cytokine treatment. Fifteen adult healthy HIV-1-seronegative donors (11 male, four female; mean age 30.5 ± 8.8 years), and 10 healthy HIV-1-seronegative children (six male, four female; mean age 5.5 ± 2.9 years) were included as control subjects. Informed consent was obtained from all participants in the study.
IL-18 was measured by a sandwich enzyme-linked immunosorbent assay (MBL, Hayashibara Biochemical Labs, Japan). Statistical analysis was performed by the Kruskal–Wallis non-parametric analysis of variance (ANOVA) test for multiple comparisons, by the Wilcoxon signed rank test for paired data, and by the Spearman rank test for paired data.
The cytokine levels of sera from the symptomatic group (category B; 533.1 ± 195.6 pg/ml, P < 0.01; Kruskal–Wallis non-parametric ANOVA test) and AIDS patients (category C; 939.1 ± 409.3 pg/ml, _P_ < 0.0001) were found to be signficantly higher than that detected in the sera of healthy controls (158.1 ± 76.9 pg/ml) (Fig. 1). No significant difference could be observed in serum IL-18 levels of the asymptomatic group (category A; 332.9 ± 179.1 pg/ml, _P_ > 0.05) (Fig. 1). Furthermore, no positive or negative correlations were evident within the AIDS group, when serum levels of IL-18 were compared with CD4 cell counts or with plasma virus loads. AIDS patients with opportunistic infections (n = 14) had IL-18 levels similar to those detected in patients who were not experiencing opportunistic infections at the time of the study (n = 2;P > 0.05).
Serum levels of IL-18 in adult HIV-1-infected patients: asymptomatic patients (n = 13), symptomatic patients (n = 8), AIDS patients (n = 16), and healthy controls (n = 15). Symptomatic and AIDS patients had significantly higher levels of IL-18 than healthy controls (P < 0.01 and P < 0.001 respectively; Kruskal–Wallis non-parametric analysis of variance test).
A significant increase in IL-18 levels was also observed in HIV-1-infected children (790.5 ± 360.7 pg/ml, P < 0.001; Kruskal–Wallis non-parametric ANOVA test) in comparison with healthy control children (122.3 ± 41.5 pg/ml), whereas in HIV-1-seronegative children, born to HIV-1-infected mothers, serum levels of IL-18 (210.1 ± 65.9 pg/ml) did not significantly increase with respect to the controls.
Furthermore, seven adult patients treated with highly active antiretroviral therapy (HAART; including a protease inhibitor; virus load 148 717 ± 194 480 copies/ml, and CD4 cell counts 300.7 ± 134.2 cells/ul) showed a significant decrease of IL-18 levels (before treatment 484.0 ± 344.9 pg/ml, and after treatment: 265.4 ± 158.4 pg/ml;P = 0.039, Wilcoxon signed rank test).
The present study demonstrates for the first time elevated levels of IL-18 in adult and paediatric patients with HIV-1 infection, which increase in accordance with disease progression. Shapiro et al. [6] suggested a role for IL-18 in HIV-1 pathogenesis because of the ability IL-18 shares with the proinflammatory cytokines IL-1 and TNF to stimulate HIV-1 production in vitro. The proinflammatory cytokines TNF and IL-6 are able to increase HIV-1 production in monocytic cells [8,9]. Shapiro et al. [6] demonstrated that there is intermediate production of IL-6 in IL-18-stimulated HIV-1 production in the U1 monocytic cell line, and because IL-6 does not induce TNF, but TNF induces IL-6, the cascade may be IL-18-induced TNF, followed by TNF-induced IL-6.
The increased production of IL-18 observed in our patients, especially in those in advanced phases of the disease, may represent an efficient and persistent stimulation of the T helper type 1 response.
On the other hand, the marked decrease in IL-18 levels, observed in patients treated with HAART, may denote a downregulation of IL-18 on HIV production from monocytes/macrophages.
In conclusion, the findings in this study of an increase in circulating IL-18 levels along with disease progression in HIV-1-infected patients, and a decline in IL-18 levels during HAART are compatible with a pathogenic role for IL-18 in these patients.
Donato Torrea
Filippo Speranzaa
Roberto Martegania
Agostino Puglieseb
Francesco Castellic
Cristina Basilicoa
Gilberto Biondia
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