Abstract.

Elevated TLR expression/signalling in monocyte/macrophages has been shown to mediate systemic immune activation, a hallmark of progressive HIV-1 infection. Here we show, via differential gene expression comparisons, the presence of a constitutive in vivo TLR-like gene activation signature in steady-state circulating monocytes from chronically HIV-1 infected subjects. The TLR2-like gene signature was defined as an 82 gene subset of the 376 genes constitutively modulated in in vivo HIV-1 monocytes, based on their overlap with de novo TLR2-induced genes in uninfected subjects’ monocytes following acute ex vivo stimulation with Staphylococcus Aureus Cowan (SAC).

Additional comparison of in vivo gene networks with available datasets from acute TLR activations in M/M expanded the overlap to 151-gene concordance among the 376 differential genes with emphasis on ERK/MAPK, TNF/IL6 (NFκB) and p53 gene networks. TLR2 stimulation of monocytes from HIV-1 infected subjects resulted in further upregulation of inflammatory genes indicative of a sustained transcriptional potential upon stimulation. In summary, our data support the presence of a sustained TLR-like gene activation profile in circulating monocyte from steady-state viremia in HIV-1 infected subjects.

Introduction.

Monocyte/macrophages (M/M) play an important role in HIV-1 infection. In addition to participating in the host anti-HIV-1 innate immune response [1], [2], [3], M/M are one of two primary cellular targets of HIV-1 [4]. M/M bind HIV-1, support virus replication [5], and serve as quiescent and long-lived viral reservoirs [6], [7], [8]. Several in vitro studies have shown functional and metabolic impairments in M/M following infection/exposure to HIV-1 [9], [10], [11], [12], [13]. Studies of global gene modulation in vitro in HIV-infected MDMs have identified HIV-induced macrophage activation profiles such as the modulation of pro-viral transcription factor genes, inflammatory, and modulation of cell cycle genes that have all been proposed to contribute to sustained viral replication [14], [15]. Unlike in vitro MDMs exposed to infectious HIV-1 where the primary contribution to gene modulation is from productive HIV-1 replication in MDM over time, the modulation of the in vivo circulating monocyte cell subset is not associated with productive monocyte infection as less than 1% are infected, gene modulation is expected to be the summation of HIV-1 virion-induced systemic changes and host-associated factors [16].

Toll Like Receptor (TLR)-mediated signalling has emerged as a major factor apart from HIV-induced signalling potentially contributing to the persistent chronic immune activation state observed during viremia. The notion that multiple TLR receptor activation outcomes could contribute to HIV-1 pathogenesis has been based on increased levels of circulating bacterial wall products in association with increased microbial translocation [17], the upregulation of TLR expression in immune cells including monocytes following HIV-1 infection [18], [19], the identification of HIV encoded TLR ligand interactions [20] and HIV-RNA mediated upregulation of TLR expression [21]. These observations question whether in vivo circulating monocytes in HIV-1 infection exhibit gene expression patterns similar to those elicited by specific TLRs [17]. To our knowledge, no direct comparison has been made in HIV-infected persons’ circulating monocyte gene expression in vivo with acute gene signatures for TLR-mediated gene activation programs in monocytes. Here, we have compared whether differential steady-state genes from circulating monocytes from HIV-infected subjects versus uninfected overlapped with de novo induced Toll-like receptor 2 gene signatures induced from uninfected subject monocytes.