Expression of interleukin-15 and interleukin-15Rα in monocytes of HIV type 1-infected patients with different courses of disease progression

Abstract

Interleukin-15 (IL-15) enhances the effector mechanisms of anti-HIV immune responses and thus is considered a potential adjuvant of HIV-1 vaccine. However, there are a lack of data concerning the relationships between IL-15 expression and regulation in HIV-1-infected patients and the course of disease progression. We found that IL-15, but not IL-15Rα, is expressed at significantly higher levels in the CD14(+) monocytes [stimulated or not with interferon (IFN)-γ] of long-term nonprogressors (LTNP) than in those of HIV-1 progressors or healthy controls. There was no between-group difference in the amounts of soluble IL-15 released from the cells. We also found that like the healthy controls, the LTNP expressed the IL-15 and IL-15Rα genes in a more coordinated manner than the progressors. Our findings show that there are significant differences in IL-15 expression between patients with different courses of HIV infection, and that the coordinated expression of the IL-15 and IL-15Rα genes is dysregulated in patients with progressive disease. They also provide important information concerning the mechanisms of infection and the potential use of IL-15 as a therapeutic agent.

FIG. 1.

Intracellular interleukin (IL)-15 and surface IL-15Rα expression in CD14⁺ monocytes. Flow cytometric analyses of peripheral blood mononuclear cells (PBMCs) isolated from HIV-1⁺ progressors (n=16), long-term nonprogressors (LTNP, n=20), and healthy controls (n=14). Intracellular IL-15 expression and IL-15Rα were analyzed on CD14⁺ monocytes in separate cell samples but in a similar way as shown in the diagram. (A) Gating of monocytes based on SS and FS (left) and CD14⁺ monocytes based on CD14 and FS (right graph). (B) Histograms representing cells accumulated in gate B (according to CD14 and FS) were used to assess the intracellular IL-15 (IL15ic in white) or IL-15Rα (in gray) expression by marking the region of positive staying (black line across the graph) outside the negative region of fluorescence obtained by use of control cells of the same patient stained with isotype control antibody (mouse IgG1 for icIL-15 or mouse IgG2b for IL-15Rα). (C) IL-15ic and IL15Rα expression in CD14⁺ monocytes. The data were analyzed using the Mann–Whitney test: *p<0.05.

FIG. 2.

Intracellular expression of IL-15 in CD14⁺ monocytes after in vitro culture with or without interferon (IFN)-γ stimulation. PBMCs isolated from HIV-1⁺ progressors (n=15), LTNP (n=17), and healthy controls (n=14) were stimulated overnight (IFN) or not (NS) with IFN-γ, and the expression of icIL-15 in CD14⁺ monocytes was analyzed by means of cytofluorimetry. The data were analyzed using a paired t test: **p<0.005.

FIG. 3.

IL-15Rα expression in CD14⁺ monocytes after IFN-γ stimulation. PBMCs isolated from HIV-1⁺ progressors (n=14), LTNP (n=18), and healthy controls (n=12) were stimulated overnight (IFN) or not (NS) with IFN-γ, and the expression of IL-15Rα in CD14⁺ monocytes was analyzed by means of cytofluorimetry. The data were analyzed using a paired t test: *p<0.05.

FIG. 4.

Correlation analyses of IL-15 and IL-15Rα gene expression. Correlations between the ΔCt (ΔCt=Ct of IL-15 or IL-15Ra – Ct of β-actin) values of IL-15 and IL-15Rα gene expression in unstimulated or IFN-γ−stimulated PBMCs from LTNP (n=20), progressors (n=14), and healthy controls (n=14). The data were analyzed by means of linear regression.

FIG. 5.

Analyses of IL-15 concentrations in the supernatants of cells stimulated or not with IFN-γ. PBMCs isolated from HIV-1⁺ progressors (n=14), LTNP (n=14), and healthy controls (n=12) were stimulated overnight (IFN) or not (NS) with IFN-γ, and the concentrations of IL-15 were assessed in the collected supernatants. The data were analyzed using a paired t test, and there were significant differences after IFN-γ stimulation in all of the groups but not between them: ***p<0.001; **p<0.005.