Plasmacytoid Dendritic Cell Infection and Sensing Capacity during Pathogenic and Nonpathogenic Simian Immunodeficiency Virus Infection.

Human immunodeficiency virus (HIV) in humans and simian immunodeficiency virus (SIV) in macaques (MAC) lead to chronic inflammation and AIDS. Natural hosts, such as African green monkeys (AGM) and sooty mangabeys (SM), are protected against SIV-induced chronic inflammation and AIDS. Here, we report that AGM plasmacytoid dendritic cells (pDC) express extremely low levels of CD4, unlike MAC and human pDC. Despite this, AGM pDC efficiently sensed SIVagm, but not heterologous HIV/SIV isolates, indicating a virus-host adaptation. Moreover, both AGM and SM pDC were found to be, in contrast to MAC pDC, predominantly negative for CCR5. Despite such limited CD4 and CCR5 expression, lymphoid tissue pDC were infected to a degree similar to that seen with CD4(+) T cells in both MAC and AGM. Altogether, our finding of efficient pDC infection by SIV in vivo identifies pDC as a potential viral reservoir in lymphoid tissues. We discovered low expression of CD4 on AGM pDC, which did not preclude efficient sensing of host-adapted viruses. Therefore, pDC infection and efficient sensing are not prerequisites for chronic inflammation. The high level of pDC infection by SIVagm suggests that if CCR5 paucity on immune cells is important for nonpathogenesis of natural hosts, it is possibly not due to its role as a coreceptor. The ability of certain key immune cell subsets to resist infection might contribute to the asymptomatic nature of simian immunodeficiency virus (SIV) infection in its natural hosts, such as African green monkeys (AGM) and sooty mangabeys (SM). This relative resistance to infection has been correlated with reduced expression of CD4 and/or CCR5. We show that plasmacytoid dendritic cells (pDC) of natural hosts display reduced CD4 and/or CCR5 expression, unlike macaque pDC. Surprisingly, this did not protect AGM pDC, as infection levels were similar to those found in MAC pDC. Furthermore, we show that AGM pDC did not consistently produce type I interferon (IFN-I) upon heterologous SIVmac/HIV type 1 (HIV-1) encounter, while they sensed autologous SIVagm isolates. Pseudotyping SIVmac/HIV-1 overcame this deficiency, suggesting that reduced uptake of heterologous viral strains underlays this lack of sensing. The distinct IFN-I responses depending on host species and HIV/SIV isolates reveal the host/virus species specificity of pDC sensing.

Jochems SP ，Jacquelin B ，Chauveau L ，Huot N ，Petitjean G ，Lepelley A ，Liovat AS ，Ploquin MJ ，Cartwright EK ，Bosinger SE ，Silvestri G ，Barré-Sinoussi F ，Lebon P ，Schwartz O ，Müller-Trutwin MC ... -  《-》

CXCR6-Mediated Simian Immunodeficiency Virus SIVagmSab Entry into Sabaeus African Green Monkey Lymphocytes Implicates Widespread Use of Non-CCR5 Pathways in Natural Host Infections.

African green monkeys (AGM) and sooty mangabeys (SM) are well-studied natural hosts of simian immunodeficiency virus (SIV) that do not progress to AIDS when infected with their species-specific viruses. Natural hosts of SIV express very low levels of the canonical entry coreceptor CCR5, and recent studies have shown that CCR5 is dispensable for SIV infection of SM in vivo and that blocking of CCR5 does not prevent ex vivo infection of peripheral blood mononuclear cells (PBMC) from SM or vervet AGM. In both hosts, CXCR6 is an efficient entry pathway in vitro Here we investigated the use of species-matched CXCR6 and other alternative coreceptors by SIVagmSab, which infects sabaeus AGM. We cloned sabaeus CD4 and 10 candidate coreceptors. Species-matched CXCR6, CCR5, and GPR15 mediated robust entry into transfected cells by pseudotypes carrying SIVagmSab92018ivTF Env, with lower-level entry through GPR1 and APJ. We cloned genetically divergent env genes from the plasma of two wild-infected sabaeus AGM and found similar patterns of coreceptor use. Titration experiments showed that CXCR6 and CCR5 were more efficient than other coreceptors when tested at limiting CD4/coreceptor levels. Finally, blocking of CXCR6 with its ligand CXCL16 significantly inhibited SIVagmSab replication in sabaeus PBMC and had a greater impact than did the CCR5 blocker maraviroc, confirming the use of CXCR6 in primary lymphocyte infection. These data suggest a new paradigm for SIV infection of natural host species, whereby a shared outcome of virus-host coevolution is the use of CXCR6 or other alternative coreceptors for entry, which may direct SIV toward CD4+ T cell subsets and anatomical sites that support viral replication without disrupting immune homeostasis and function. Natural hosts of SIV do not progress to AIDS, in stark contrast to pathogenic human immunodeficiency virus type 1 (HIV-1)-human and SIVmac-macaque infections. Identifying how natural hosts avoid immunodeficiency can elucidate key mechanisms of pathogenesis. It is known that despite high viral loads, natural hosts have a low frequency of CD4+ cells expressing the SIV coreceptor CCR5. In this study, we demonstrate the efficient use of the coreceptor CXCR6 by SIVagmSab to infect sabaeus African green monkey lymphocytes. In conjunction with studies of SIVsmm, which infects sooty mangabeys, and SIVagmVer, which infects vervet monkeys, our data suggest a unifying model whereby in natural hosts, in which the CCR5 expression level is low, the use of CXCR6 or other coreceptors to mediate infection may target SIV toward distinct cell populations that are able to support high-level viral replication without causing a loss of CD4+ T cell homeostasis and lymphoid tissue damage that lead to AIDS in HIV-1 and SIVmac infections.

Wetzel KS ，Yi Y ，Elliott STC ，Romero D ，Jacquelin B ，Hahn BH ，Muller-Trutwin M ，Apetrei C ，Pandrea I ，Collman RG ... -  《-》

Simian Immunodeficiency Virus SIVagm Efficiently Utilizes Non-CCR5 Entry Pathways in African Green Monkey Lymphocytes: Potential Role for GPR15 and CXCR6 as Viral Coreceptors.

African green monkeys (AGM) are natural hosts of simian immunodeficiency virus (SIV), and infection in these animals is generally nonpathogenic, whereas infection of nonnatural hosts, such as rhesus macaques (RM), is commonly pathogenic. CCR5 has been described as the primary entry coreceptor for SIV in vivo, while human-derived CXCR6 and GPR15 also appear to be used in vitro. However, sooty mangabeys that are genetically deficient in CCR5 due to an out-of-frame deletion are infectible with SIVsmm, indicating that SIVsmm can use alternative coreceptors in vivo. In this study, we examined the CCR5 dependence of SIV strains derived from vervet AGM (SIVagmVer) and the ability of AGM-derived GPR15 and CXCR6 to serve as potential entry coreceptors. We found that SIVagmVer replicated efficiently in AGM and RM peripheral blood mononuclear cells (PBMC) in the presence of the CCR5 antagonist maraviroc, despite the fact that maraviroc was capable of blocking the CCR5-tropic strains SIVmac239, SIVsmE543-3, and simian-human immunodeficiency virus SHIV-AD8 in RM PBMC. We also found that AGM CXCR6 and AGM GPR15, to a lesser extent, supported entry of pseudotype viruses bearing SIVagm envelopes, including SIVagm transmitted/founder envelopes. Lastly, we found that CCR5, GPR15, and CXCR6 mRNAs were detected in AGM and RM memory CD4(+) T cells. These results suggest that GPR15 and CXCR6 are expressed on AGM CD4(+) T cells and are potential alternative coreceptors for SIVagm use in vivo. These data suggest that the use of non-CCR5 entry pathways may be a common feature of SIV replication in natural host species, with the potential to contribute to nonpathogenicity in these animals. African green monkeys (AGM) are natural hosts of SIV, and infection in these animals generally does not cause AIDS, whereas SIV-infected rhesus macaques (RM) typically develop AIDS. Although it has been reported that SIV generally uses CD4 and CCR5 to enter target cells in vivo, other molecules, such as GPR15 and CXCR6, also function as SIV coreceptors in vitro. In this study, we investigated whether SIV from vervet AGM can use non-CCR5 entry pathways, as has been observed in sooty mangabeys. We found that SIVagmVer efficiently replicated in AGM and RM peripheral blood mononuclear cells in the presence of the CCR5 antagonist maraviroc, suggesting that non-CCR5 entry pathways can support SIVagm entry. We found that AGM-derived GPR15 and CXCR6 support SIVagmVer entry in vitro and may serve as entry coreceptors for SIVagm in vivo, since their mRNAs were detected in AGM memory CD4(+) T cells, the preferred target cells of SIV.

Riddick NE ，Wu F ，Matsuda K ，Whitted S ，Ourmanov I ，Goldstein S ，Goeken RM ，Plishka RJ ，Buckler-White A ，Brenchley JM ，Hirsch VM ... -  《-》

Modulation of type I interferon-associated viral sensing during acute simian immunodeficiency virus infection in African green monkeys.

Natural hosts of simian immunodeficiency virus (SIV), such as African green monkeys (AGMs), do not progress to AIDS when infected with SIV. This is associated with an absence of a chronic type I interferon (IFN-I) signature. It is unclear how the IFN-I response is downmodulated in AGMs. We longitudinally assessed the capacity of AGM blood cells to produce IFN-I in response to SIV and herpes simplex virus (HSV) infection. Phenotypes and functions of plasmacytoid dendritic cells (pDCs) and other mononuclear blood cells were assessed by flow cytometry, and expression of viral sensors was measured by reverse transcription-PCR. pDCs displayed low BDCA-2, CD40, and HLA-DR expression levels during AGM acute SIV (SIVagm) infection. BDCA-2 was required for sensing of SIV, but not of HSV, by pDCs. In acute infection, AGM peripheral blood mononuclear cells (PBMCs) produced less IFN-I upon SIV stimulation. In the chronic phase, the production was normal, confirming that the lack of chronic inflammation is not due to a sensing defect of pDCs. In contrast to stimulation by SIV, more IFN-I was produced upon HSV stimulation of PBMCs isolated during acute infection, while the frequency of AGM pDCs producing IFN-I upon in vitro stimulation with HSV was diminished. Indeed, other cells started producing IFN-I. This increased viral sensing by non-pDCs was associated with an upregulation of Toll-like receptor 3 and IFN-γ-inducible protein 16 caused by IFN-I in acute SIVagm infection. Our results suggest that, as in pathogenic SIVmac infection, SIVagm infection mobilizes bone marrow precursor pDCs. Moreover, we show that SIV infection modifies the capacity of viral sensing in cells other than pDCs, which could drive IFN-I production in specific settings. The effects of HIV/SIV infections on the capacity of plasmacytoid dendritic cells (pDCs) to produce IFN-I in vivo are still incompletely defined. As IFN-I can restrict viral replication, contribute to inflammation, and influence immune responses, alteration of this capacity could impact the viral reservoir size. We observed that even in nonpathogenic SIV infection, the frequency of pDCs capable of efficiently sensing SIV and producing IFN-I was reduced during acute infection. We discovered that, concomitantly, cells other than pDCs had increased abilities for viral sensing. Our results suggest that pDC-produced IFN-I upregulates viral sensors in bystander cells, the latter gaining the capacity to produce IFN-I. These results indicate that in certain settings, cells other than pDCs can drive IFN-I-associated inflammation in SIV infection. This has important implications for the understanding of persistent inflammation and the establishment of viral reservoirs.

Jochems SP ，Petitjean G ，Kunkel D ，Liovat AS ，Ploquin MJ ，Barré-Sinoussi F ，Lebon P ，Jacquelin B ，Müller-Trutwin MC ... -  《-》

Dualtropic CXCR6/CCR5 Simian Immunodeficiency Virus (SIV) Infection of Sooty Mangabey Primary Lymphocytes: Distinct Coreceptor Use in Natural versus Pathogenic Hosts of SIV.

Natural-host sooty mangabeys (SM) infected with simian immunodeficiency virus (SIV) exhibit high viral loads but do not develop disease, whereas infection of rhesus macaques (RM) causes CD4(+) T cell loss and AIDS. Several mechanisms have been proposed to explain these divergent outcomes, including differences in cell targeting, which have been linked to low expression of the canonical SIV entry receptor CCR5 on CD4(+) T cells of SM and other natural hosts. We previously showed that infection and high-level viremia occur even in a subset of SM that genetically lack functional CCR5, which indicates that alternative entry coreceptors are used by SIV in vivo in these animals. We also showed that SM CXCR6 is a robust coreceptor for SIVsmm in vitro. Here we identify CXCR6 as a principal entry pathway for SIV in SM primary lymphocytes. We show that ex vivo SIV infection of lymphocytes from CCR5 wild-type SM is mediated by both CXCR6 and CCR5. In contrast, infection of RM lymphocytes is fully dependent on CCR5. These data raise the possibility that CXCR6-directed tropism in CCR5-low natural hosts may alter CD4(+) T cell subset targeting compared with that in nonnatural hosts, enabling SIV to maintain high-level replication without leading to widespread CD4(+) T cell loss. Natural hosts of SIV, such as sooty mangabeys, sustain high viral loads but do not develop disease, while nonnatural hosts, like rhesus macaques, develop AIDS. Understanding this difference may help elucidate mechanisms of pathogenesis. Natural hosts have very low levels of the SIV entry coreceptor CCR5, suggesting that restricted entry may limit infection of certain target cells, although it is unclear how the virus replicates so robustly. Here we show that in sooty mangabey lymphocytes, infection is mediated by the alternative entry coreceptor CXCR6, as well as CCR5. In rhesus macaque lymphocytes, however, infection occurs entirely through CCR5. The use of CXCR6 for entry, combined with very low CCR5 levels, may redirect the virus to different cell targets in natural hosts. It is possible that differential targeting may favor infection of nonessential cells and limit infection of critical cells in natural hosts, thus contributing to benign outcome of infection.

Elliott ST ，Wetzel KS ，Francella N ，Bryan S ，Romero DC ，Riddick NE ，Shaheen F ，Vanderford T ，Derdeyn CA ，Silvestri G ，Paiardini M ，Collman RG ... -  《-》