Capture and transfer of HIV-1 particles by mature dendritic cells converges with the exosome-dissemination pathway

Abstract

Exosomes are secreted cellular vesicles that can be internalized by dendritic cells (DCs), contributing to antigen-specific naive CD4 ؉ T-cell activation. Here, we demonstrate that human immunodeficiency virus type 1 (HIV-1) can exploit this exosome antigen-dissemination pathway intrinsic to mature DCs (mDCs) for mediating trans-infection of T lymphocytes. Capture of HIV-1, HIV-1 Gag-enhanced green fluorescent protein (eGFP) virallike particles (VLPs), and exosomes by DCs was up-regulated upon maturation, resulting in localization within a CD81 ؉ compartment. Uptake of VLPs or exosomes could be inhibited by a challenge with either particle, suggesting that the expression of common determinant(s) on VLP or exosome surface is necessary for internalization by mDCs. Capture by mDCs was insensitive to proteolysis but blocked when virus, VLPs, or exosomes were produced from cells treated with sphingolipid biosynthesis inhibitors that modulate the lipid composition of the budding particles. Finally, VLPs and exosomes captured by mDCs were transmitted to T lymphocytes in an envelope glycoproteinindependent manner, underscoring a new potential viral dissemination pathway. IntroductionDendritic cells (DCs) are specialized antigen-presenting cells that orchestrate innate and adaptive immune responses to invading pathogens. Immature DCs located in the peripheral mucosal tissues recognize and capture microbial pathogens, undergo maturation, and traffic to lymphoid tissues, where they induce adaptive immunity through antigen presentation to naive T cells. Although DCs are required to combat viral infections, viruses, including human immunodeficiency virus type 1 (HIV-1), have evolved strategies to evade their antiviral activity. HIV can gain access into DCs via a nonfusogenic endocytic mechanism, evade classical degradation pathways, and establish productive infection of DCinteracting T cells, a well-studied but poorly understood mechanism of HIV trans-infection of CD4 ϩ T cells. [1][2][3] The efficiency of DC-mediated HIV-1 transmission to T cells can be enhanced by maturing DCs in vitro, 2,4,5 although the mechanism underlying this process has not been well defined. 6 Previous studies have associated HIV trans-infection with the binding of the viral envelope glycoprotein (gp120) to C-type lectin receptors (CLR) such as DC-SIGN, trypsin-sensitive CLR, and CD4-independent receptors expressed on the DC surface. 3,7-11 However, we have recently identified an HIV gp120-independent mechanism of viral binding and endocytosis that is up-regulated upon DC maturation, 12 suggesting that HIV-1 might exploit a preexisting cellular pathway of antigen uptake and transmission. Interestingly, previous reports have shown that DCs can endocytose viral-like particles (VLPs) and induce immune responses. 13,14 Likewise, small secreted cellular organelles, termed exosomes, are also internalized by DCs and sorted into an endocytic compartment, stimulating antigenspecific naive CD4 ϩ T-cell activation in vivo. 15,16 On the basis of similarities i...

HIV-1 Capture and Antigen Presentation by Dendritic Cells: Enhanced Viral Capture Does Not Correlate with Better T Cell Activation

“…Confirming our results by p24 Gag ELISA (Fig. 1, middle panel), mDC LPS captured higher amounts of viral particles, concentrating them in a large sac-like compartment, as previously described (10,28). In contrast, mDC ITIP showed a random distribution of captured HIV-1, more similar to iDC than to mDC LPS.…”

“…These results strongly suggest that HIV-1 capture by mDC LPS does not route HIV-1 virions toward degradation compartments and HLA loading. Our results are reminiscent of the observations that localization of captured virus differs between iDC and mDC (36), because mDC, but not iDC, accumulate whole virions in a nonconventional endocytic compartment rich in tetraspanins with a mildly acidic pH (6,10,37). In addition, HLA-II Ag presentation depends on viral degradation in acidified endosomes (34); however, inhibition of endosomal acidification preserves HIV-1 infectivity (38).…”

“…It was proposed that HIV-1 takes advantage of a pre-existing exosome Ag-dissemination pathway intrinsic to mDC to enable final trans-infection of CD4 + T cells (10)(11)(12), whereas others investigators adduce that only DC surface-bound HIV-1 are able to trans-infect target cells (13). However, both models have been reconciled, demonstrating that LPS-matured DC (mDC LPS) concentrate HIV-1 in a tetra-spanin-rich compartment that remains physically connected to the extracellular milieu (9).…”

Exosomes as intercellular signalosomes and pharmacological effectors

“…HIV and exosome feature a similar size and share some protein content [82]; and HIV virions are partly Page 13 of 32 A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 13 generated into the MVB [82]. In addition recent developments demonstrated that HIV enters the endocytic track of target cells for infection [83].…”

“…When infected, dendritic cells, monocytes, macrophages and lymphocytes can produce both exosomes and HIV virions [82] with similar density, which require separation by immunocapture or appropriate gradient density separation. Also exosomes compete with HIV for the virus entry in endocytic compartment [83]. About 10% proteins are identical between HIV virions and exosomes issued from the same cell type [82].…”