Toll-like receptor 3 activation selectively reverses HIV latency in microglial cellsReport as inadecuate

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, 14:9

First Online: 06 February 2017Received: 09 August 2016Accepted: 19 January 2017


BackgroundMultiple toll-like receptors TLRs are expressed in cells of the monocytic lineage, including microglia, which constitute the major reservoir for human immunodeficiency virus HIV infection in the brain. We hypothesized that TLR receptor mediated responses to inflammatory conditions by microglial cells in the central nervous system CNS are able to induce latent HIV proviruses, and contribute to the etiology of HIV-associated neurocognitive disorders.

ResultsNewly developed human microglial cell lines hµglia, obtained by immortalizing human primary microglia with simian virus-40 SV40 large T antigen and the human telomerase reverse transcriptase, were used to generate latently infected cells using a single-round HIV virus carrying a green fluorescence protein reporter hµglia-HIV, clones HC01 and HC69. Treatment of these cells with a panel of TLR ligands showed surprisingly that two potent TLR3 agonists, poly I:C and bacterial ribosomal RNA potently reactivated HIV in hμglia-HIV cells. LPS TLR4 agonist, flagellin TLR5 agonist, and FSL-1 TLR6 agonist reactivated HIV to a lesser extent, while Pam3CSK4 TLR2-1 agonist and HKLM TLR2 agonist only weakly reversed HIV latency in these cells. While agonists for TLR2-1, 4, 5 and 6 reactivated HIV through transient NF-κB induction, poly I:C, the TLR3 agonist, did not activate NF-κB, and instead induced the virus by a previously unreported mechanism mediated by IRF3. The selective induction of IRF3 by poly I:C was confirmed by chromatin immunoprecipitation ChIP analysis. In comparison, in latently infected rat-derived microglial cells hT-CHME-5-HIV, clone HC14, poly I:C, LPS and flagellin were only partially active. The TLR response profile in human microglial cells is also distinct from that shown by latently infected monocyte cell lines THP-1-HIV, clone HA3, U937-HIV, clone HUC5, and SC-HIV, clone HSCC4, where TLR2-1, 4, 5, 6 or 8, but not for TLR3, 7 or 9, reactivated HIV.

ConclusionsTLR signaling, in particular TLR3 activation, can efficiently reactivate HIV transcription in infected microglia, but not in monocytes or T cells. The unique response profile of microglial cells to TLR3 is fundamental to understanding how the virus responds to continuous microbial exposure, especially during inflammatory episodes, that characterizes HIV infection in the CNS.

KeywordsHIV latency Toll-like receptors TLR3 Microglial cells HIV-associated neurocognitive disorders AbbreviationsHIVhuman immuno-deficiency virus

TLRstoll-like receptors

CNScentral nervous system

HANDHIV-associated neurocognitive disorders

GFPgreen fluorescence protein

MtbMycobacterium tuberculosis

hµglia-HIVhuman immortalized microglial cells latently-infected with HIV

SV40Tagsimian virus 40 T antigen


NF-κBnuclear factor kappa-light-chain-enhancer of activated B cells

HAARThighly-active anti-retroviral therapy

hTERThuman telomerase reverse transcriptase

LTRlong terminal repeats

TNF-αtissue necrosis factor α

TCRT cell receptor

PCRpolymerase chain reaction

HDAChistone deacetylase

PIpropidium iodide

SDS-PAGEsodium dodecyl sulfate polyacrylamide gel electrophoresis

WCEwhole cell extracts

NBDNEMO binding domain



ManLAMmannosylated lipoarabinomannan

PIMphosphatidylinositol mannoside

ChIPchromatin immunoprecipitation

MNasemicrococcal nuclease

Electronic supplementary materialThe online version of this article doi:10.1186-s12977-017-0335-8 contains supplementary material, which is available to authorized users.

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Author: David Alvarez-Carbonell - Yoelvis Garcia-Mesa - Stephanie Milne - Biswajit Das - Curtis Dobrowolski - Roxana Rojas - Jonatha


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