Introduction: Macrophages act as a reservoir and source for dissemination of virus during HIV-1 infection. They support persistent HIV-1 replication and, in contrast to infected T cells, demonstrate lower viral productivity. Only some of the factors responsible for these biological differences have been identified. We have shown that HIV-1BaL can directly induce a subset of interferon-stimulated genes (ISGs) in monocyte-derived macrophages (MDMs), dendritic cells (MDDC) and T-cells in the absence of interferon induction by blocking interferon regulatory factor 3 translocation to the nucleus. The specific subsets of ISGs induced in each cell type were unique. In MDMs, viperin was the most upregulated ISG followed by interferon-induced protein with tetratricopeptide repeats (IFITs). In this study we are investigating how HIV blocks IRF3 nuclear translocation and whether IFITs also play a role in negatively modulating HIV replication in MDMs.
Results: we showed that IRF3 becomes phosphorylated in MDMs exposed to LPS but not in cells infected with HIV-1. In addition we show that the IRF3 kinases TBK1 and IKKE are not targeted to the proteasome. siRNA knockdown of IFIT1, IFIT2 and IFIT3 in MDMs was successful and led to a consistent increase in extracellular virus suggesting that the HIV-driven IFIT proteins may act to restrict HIV-1 production, but this did not affect the inter-cell spread. Currently we are investigating the inhibition of HIV-1 replication in HEK293s following the transfection of Viperin, IFIT1, IFIT2 and IFIT3 alone or in combination.
Discussion: We propose that viperin in combination with other ISGs expressed at lower levels in macrophages, contributes to the relative resistance to HIV-1 induced cell death and to the restricted production of HIV-1 compared to T cells. In addition we show that HIV blocks IRF3 phosphorlyation but this block is not mediated by targeting IRF3 kinases (TBK1 and IKKE) to the proteasome.