Differential regulation of toll-like receptor pathways in acute and chronic HIV-1 infection

Abstract

Objective and design: The objective of this study was to determine changes in toll-like receptor (TLR) responses of monocytes, myeloid dendritic cells and plasmacytoid dendritic cells during primary and chronic HIV-1 infection. TLRs serve as important innate receptors to sense pathogens, and have been implicated in mediating immune activation in HIV-1 infection. Studies assessing the consequences of HIV-1 infection on the ability of innate immune cells to respond to TLR stimulation have come to varying conclusions.

Methods: Using intracellular flow cytometry, cytokine production by cryopreserved peripheral blood mononuclear cells from healthy controls and HIV-1-infected individuals were examined after TLR stimulation.

Results: We observed that the effect of HIV-1 infection on TLR responses not only depended on the stage of HIV-1 infection, but was also dependent on the individual receptor and cell type examined. Monocyte and myeloid dendritic cell responses to TLR8 stimulation were associated with HIV-1 viral load and CD4 T-cell count, whereas plasmacytoid dendritic cell responses to TLR7 stimulation were not. Responses to TLR2 stimulation were not affected by HIV-1 infection, whereas responses to TLR9 stimulation were universally decreased in all HIV-1-infected individuals examined regardless of treatment or clinical parameters.

Conclusion: Responsiveness to TLR7/8 stimulation, which have been shown to recognize HIV-1 ssRNA, did not decrease in chronic infection, and may represent a contributing factor to ongoing T-cell immune activation in the setting of chronic viremic HIV-1 infection.

Figures

Figure 1. Monocyte and dendritic cell responses to TLR stimulation

Cryopreserved PBMCs previously isolated from HIV-1 negative controls (HIV-, open squares), elite controllers (EC; closed circles), treated chronically HIV-1-infected individuals (Rx+, closed square), untreated chronically HIV-1-infected individuals (Rx-, inverted closed triangle), and individuals with primary HIV-1 infection (Primary, closed triangles), were stimulated with TLR7/8 (CL097), TLR2 (HKLM) and TLR9 (CpG) ligands. Intracellular cytokine production was measured in (A) monocytes, (B) myeloid dendritic cells (mDC), (C) and plasmacytoid dendritic cells (pDCs). Results are expressed as the percentage of cytokine producing cells. Means and standard deviations are shown in the graph.

Figure 2. Correlation between monocyte and dendritic cells responses to TLR7/8 and CD4+ T cell count and HIV-1 viral load

Monocyte, mDC and pDC production of TNFα in response to TLR7/8 ligand (CL097) stimulation were correlated to CD4+ T cell count (top graphs) and HIV-1 viral load (bottom graphs). Where a significant correlation was observed the line of best fit is shown with the correlation coefficient and P-values.

Figure 3. Monocyte and dendritic cells TLR7/8 responses in early and late sampling of individuals with primary HIV-1 infection

(A) HIV-1 viral load and CD4+ T cell count of primary HIV-1-infected individuals who were treated (Rx+; solid diamonds) or remained untreated (Rx-; solid squares) during the early (within first two months of infection) and late (23-58 weeks later) time points are shown. In addition, data for treated (Rx+, Chronic) and untreated (Rx-, Chronic) chronically HIV-1-infected individuals were also included. (B) The corresponding TLR7/8 responses as measured by monocyte, mDCs and pDCs TNFα production were measured in individuals during the early and late primary HIV-1 infection and subjects with treated (Rx+) or untreated (Rx-) chronic HIV-1 infection. Differences were calculated using either paired t-test or Wilcoxon Rank tests (Mann Whitney).