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...

Mutations in leucine-rich repeat kinase 2 (LRRK2) cause autosomal-dominant familial Parkinson's disease. We generated lines of Caenorhabditis elegans expressing neuronally directed human LRRK2. Expressing human LRRK2 increased nematode survival in response to rotenone or paraquat, which are agents that cause mitochondrial dysfunction. Protection by G2019S, R1441C, or kinase-dead LRRK2 was less than protection by wild-type LRRK2. Knockdown of lrk-1, the endogenous ortholog of LRRK2 in C. elegans, reduced survival associated with mitochondrial dysfunction. C. elegans expressing LRRK2 showed rapid loss of dopaminergic markers (DAT::GFP fluorescence and dopamine levels) beginning in early adulthood. Loss of dopaminergic markers was greater for the G2019S LRRK2 line than for the wild-type line. Rotenone treatment induced a larger loss of dopamine markers in C. elegans expressing G2019S LRRK2 than in C. elegans expressing wild-type LRRK2; however, loss of dopaminergic markers in the G2019S LRRK2 nematode lines was not statistically different from that in the control line. These data suggest that LRRK2 plays an important role in modulating the response to mitochondrial inhibition and raises the possibility that mutations in LRRK2 selectively enhance the vulnerability of dopaminergic neurons to a stressor associated with Parkinson's disease.

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