Systemic immune activation in HIV infection is associated with decreased MDC responsiveness to TLR ligand and inability to activate naive CD4 T-cells

Abstract

Background: HIV infection is characterized by ineffective anti-viral T-cell responses and impaired dendritic cell (DC) functions, including response to Toll-Like Receptor (TLR) ligands. Because TLR responsiveness may affect a host's response to virus, we examined TLR ligand induced Myeloid and Plasmacytoid DC (MDC and PDC) activation of naïve T-cells in HIV+ subjects.

Methods: Freshly purified MDC and PDC obtained from HIV+ subjects and healthy controls were cultured in the presence and absence of TLR ligands (poly I∶C or R-848). We evaluated indices of maturation/activation (CD83, CD86, and HLA-DR expression), cytokine secretion (IFN-alpha and IL-6), and ability to activate allogeneic naïve CD4 T-cells to secrete IFN-gamma and IL-2.

Results: MDC from HIV+ subjects had increased spontaneous IL-6 production and increased CD83 and CD86 expression when compared to MDC of controls. MDC IL-6 expression was associated with plasma HIV level. At the same time, poly I∶C induced HLA-DR up-regulation on MDC was reduced in HIV+ persons when compared to controls. The latter finding was associated with impaired ability of MDC from HIV+ subjects to activate allogeneic naïve CD4 T-cells. PDC from HIV+ persons had increased spontaneous and TLR ligand induced IL-6 expression, and increased HLA-DR expression at baseline. The latter was associated with an intact ability of HIV PDC to activate allogeneic naïve CD4 T-cells.

Conclusion: These results have implications for the ability of the HIV+ host to form innate and adaptive responses to HIV and other pathogens.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. HIV subject DC exhibit increased maturation.

Panel A. Representative flow cytometric analysis of freshly isolated MDC and PDC from one healthy control. Mean Fluorescent Intensity (MFI) for HLA-DR, CD86, and CD83 were analyzed. Panel B. Baseline activation/maturation phenotype of freshly isolated MDC and PDC from healthy control (n = 22) and HIV+ subjects (n = 24). The black line represents the median MFI value for each group for HLA-DR, CD86, and CD83.

Figure 2. DC TLR ligand responsiveness.

Panels A and B. CD86 MFI and HLA-DR MFI on isolated MDC following overnight culture in presence of Medium and poly I∶C stimulation in healthy control (n = 21) and HIV+ subjects (n = 18). The p value in panel B is for comparison between the delta HLA-DR MFI for controls and HIV infected subjects . IL-6 production from isolated MDC on a subset of the same subjects (n = 18 control and n = 16 HIV+) (panel C) following overnight culture in absence and presence of poly I∶C stimulation. IL-6 production from isolated PDC on a subset of the same subjects (n = 17 control and n = 17 HIV+) (panel D) following overnight culture in absence and presence of R848 stimulation. Healthy control (n = 17) and HIV+ subject (n = 16) PDC IFN-α production in response to overnight R848 stimulation is shown in panel E. Panel . Association between MDC spontaneous IL-6 production and HIV plasma level.

Figure 3. HIV subject MDC are impaired in naïve CD4 T cell activation activity.

Freshly prepared MDC from healthy control (n = 17) and HIV+ (n = 18) subjects were used in titrated numbers (x-axis) to activate one healthy control subject's allogeneic naive CD4 T-cells to produce IFN-γ or IL-2 (y-axis) in a 72-h culture performed in the absence (Medium, panels A. and C.), or presence of poly I∶C (panels B. and D.). Control cultures of TLR ligand and naïve CD4 T cells resulted in <3 sfu IFN-γ, and data shown are sfu above this background.

Figure 4. HIV subject PDC are intact for naïve CD4 T cell activation activity.

Freshly prepared PDC from healthy control (n = 13) and HIV+ (n = 10) subjects were used in titrated numbers (x-axis) to activate one healthy control subject's allogeneic naive CD4 T-cells to produce IFN-γ or IL-2 (y-axis) in a 72-h culture performed in the absence (Medium, panels A. and C.), or presence of R848 (panels B. and D.). Control cultures of TLR ligand and naïve CD4 T cells resulted in <3 sfu IFN-γ, and data shown are sfu above this background.

Figure 5. Increased PDL-1 and PDL-2 expression on HIV subject MDC.

Isolated MDC were evaluated for expression of inhibitory molecules PDL-1 (panel A) and PDL-2 (panel B) in control (n = 10) and HIV+ (n = 10) subjects. Black lines represent median MFI value for each group. Panel C. Association between PDL-1 MFI on MDC in HIV+ subjects and plasma HIV level. Panel D. The percentage of Annexin V+ T-cells are shown following naive T-cell co-cultures with control vs. HIV+ subject MDC (10,000cells/well) in the absence and presence of poly I∶C.