Interleukin-37 Expression Is Increased in Chronic HIV-1-Infected Individuals and Is Associated with Inflammation and the Size of the Total Viral Reservoir

Abstract

Interleukin-37 (IL-37) is a recently identified cytokine with potent antiinflammatory and immunosuppressive functions. The objective of this study was to compare levels of IL-37 mRNA in immunological subgroups of chronic human immunodeficiency virus-1 (HIV-1)-infected individuals and noninfected controls, to determine IL-37's association with biomarkers of inflammation and reservoir size. This was a cross-sectional study. The HIV-1-infected patients were categorized in three subgroups depending on their combination antiretroviral therapy (cART) treatment status and CD4(+) T-cell count. Quantitative RT-PCR was used for the detection of IL-37 mRNA and HIV-1 DNA in peripheral blood mononuclear cells (PBMCs). Biomarkers in plasma were quantified by enzyme-linked immunosorbent assay (ELISA), whereas T-cell activation was determined by flow cytometry. Lastly, lipopolysaccharide (LPS) stimulations of patients PBMCs were carried out to determine differences in IL-37 mRNA response between the subgroups. Sixty HIV-1-infected patients and 20 noninfected controls were included in the study. Steady-state IL-37 mRNA levels in PBMCs were significantly higher in HIV-1-infected individuals compared with noninfected controls: 2.4-fold (p ≤ 0.01) cART-naïve subjects; 3.9-fold (p ≤ 0.0001) inadequate immunological responders; and 4.0-fold (p ≤ 0.0001) in immunological responders compared with non-infected controls. Additionally, levels of the monocyte inflammatory marker sCD14 correlated with IL-37 mRNA (p = 0.03), whereas there was no association with T-cell activation. Finally, we observed a significant correlation between total viral HIV-1 DNA and IL-37 mRNA in PBMCs (p < 0.0001). Collectively, our data shows that the level of IL-37 mRNA is affected by chronic HIV-1-infection. A relationship with the activation of the monocyte compartment is suggested by the correlation with sCD14 and, interestingly, IL-37 could be related to the size of the total viral HIV-1 reservoir.

Figure 1

IL-37 mRNA levels in PBMCs of HIV-1-infected patients. Levels of mRNA per copies of U6 for each of the four patient groups (noninfected controls, cART-naïve, IIRs and responders). The P value above each group corresponds to the comparison made to noninfected controls using Holm-Sidak multiple comparisons test. Depicted are group mean with standard error of the mean (SEM).

Figure 2

IL-37 mRNA levels in PBMCs of HIV-1-infected patients normalized to monocyte proportions. Levels of mRNA per copies of U6 for each of the four patient groups (noninfected controls, cART-naïve, IIRs and responders), normalized to monocyte percentages in the PBMCs. The P value above each group corresponds to the comparison made to noninfected controls using Holm-Sidak multiple comparisons test. Depicted are group mean with standard error of the mean (SEM).

Figure 3

IL-37 mRNA levels with- and without stimulation. Levels of mRNA per copies of U6 both with and without simulation for each of the four patient groups: noninfected (n = 19/20/20 [PBMC/RPMI/LPS]); cART-naïve (n = 15/19/18); IIRs (n = 20/14/14); and responders (n = 19/19/19). The P value corresponds to the comparison between the LPS-stimulated cART-naïve and IIRs. The significance levels indicated by asterisks (^**p < 0.01; ^***p < 0.001; ^****p < 0.0001) correspond to the comparison made to non-infected controls all using Holm-Sidak multiple comparisons test. Depicted are group mean with SEM.

Figure 4

Levels of sCD14 in plasma and correlation with IL-37 mRNA. (A) Levels of sCD14 in plasma for each of the four patient groups (noninfected controls, cART-naïve, IIRs and responders). The P value above each group corresponds to the comparison made to non-infected controls using Holm-Sidak multiple comparisons test (ns; nonsignificant). Depicted are group mean with SEM. (B) Levels of sCD14 in plasma compared with the levels of IL-37 mRNA in PBMCs using Spearman correlation (r = 0.25).

Figure 5

Levels of sCD163 in plasma and correlation with IL-37 mRNA. (A) Levels of sCD163 in plasma for each of the four patient groups (noninfected controls, cART-naïve, IIRs and responders). The P value above each group corresponds to the comparison made to noninfected controls using Dunn’s multiple comparisons test (ns, nonsignificant). Depicted are group mean with SEM. (B) Levels of sCD163 in plasma compared with the levels of IL-37 mRNA in PBMCs using Pearson correlation (r = −0.06)

Figure 6

Correlation between the total viral reservoir and IL-37 mRNA in PBMCs. Levels of IL-37 mRNA compared with the size of the total viral reservoir (HIV-1 DNA copies/10⁶ PBMCs) both with (B) and without (A) LPS stimulation. P values corresponds to the correlation between IL-37 mRNA and HIV-1 DNA using Spearman correlation (r = 0.33 [PBMC]; r = 0.67 [LPS]).