Mechanistic differences in interactions of HIV-1 and HIV-2 with dendritic cells
Kijewski, Suzanne Delight Geer
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Pathogenic mechanisms that account for the dramatic differences between the HIV-1 and HIV-2 epidemics remain unknown. Myeloid dendritic cells (DCs) are sentinels of the immune system, which sense invading pathogens and initiate immune responses. I hypothesize that failure of HIV-2 to overcome DC-intrinsic defense mechanisms results in diminished virus replication and reduced pathogenesis in vivo. Recent studies from our laboratory have identified capture of HIV-1 by CD169 (Siglec1), which results in preservation of virus infectivity in peripheral non-lysosomal compartments and transfer to CD4+ T cells, a mechanism of DC-mediated trans infection. HIV-1 interaction with CD169 was dependent on incorporation of a ganglioside, GM3, in the virus particle membrane. We hypothesized that reduced interaction of HIV-2 with CD169 is crucial for its attenuated pathogenic phenotype in vivo. Interestingly, HIV-2 virion assembly sites were divergent from HIV-1, which correlated with reduced incorporation of GM3 in HIV-2 virions, and a significant decrease in capture of HIV-2 compared to HIV-1 by mature DCs. Furthermore, reduced CD169-dependent HIV-2 capture by DCs attenuated access of HIV-2 to DC-mediated trans infection. In contrast to the trans infection pathway, HIV-2 could establish productive infection in DCs, though productive infection of DCs by HIV-2 resulted in innate immune activation, induction of IFN-α production and attenuated spread of virus in DC – CD4+ T cell co-cultures. As opposed to HIV-2, productive infection of DCs by HIV-1 was attenuated and failed to trigger type I IFN responses, thus allowing for efficient spread of HIV-1 in DC – CD4+ T cell co-cultures. These results suggest that immune sensing of HIV-2 in productively infected DCs limits viral spread. Finally, we investigated GM3-expressing nanoparticles (GM3-NPs) for delivery of therapeutics that trigger innate immune responses in CD169+ myeloid cells as a novel strategy to mimic myeloid cell-intrinsic virus control observed in HIV-2 infection. We tested the ability of GM3-coated nanoparticles that incorporated a TLR2 ligand, Pam3CSK4, to activate CD169+ cells. Interestingly, Pam3CSK4 containing GM3-NPs robustly activated CD169+ cells. These results suggest that induction of dendritic cell-intrinsic type I IFN responses might be a fruitful therapeutic strategy to restrict HIV-1 replication in vivo.