The increased replicative capacity of a late-stage simian immunodeficiency virus mne variant is evident in macrophage- or dendritic cell-T-cell cocultures.

Human and simian immunodeficiency virus (HIV and SIV) may co-opt antigen capture and presentation functions of antigen presenting cells (APCs) to facilitate infection of CD4+ T-cells. To address whether the replicative capacity of SIV in the host may be associated with the extent of viral replication in response to APC-T-cell interactions, we compared the replicative phenotypes of cloned early and late-stage SIVmne variants of known pathogenicity. Here, we show that the highly pathogenic late variant SIVmne027 replicates more efficiently in both macrophage- and dendritic cell (DC)-T-cell cocultures than the minimally pathogenic early virus SIVmneCl8. Contact between either macrophages or DC and T-cells increases replication of SIVmne027. Our analysis also demonstrates that mutations in pol and nef contribute to the greater replicative capacity of SIVmne027 in DC- or macrophage-T-cell cocultures. Together, these data suggest that variant viruses that evolve to replicate vigorously in response to APC-T-cell interactions may have increased replicative capacity in vivo.

Capture and transfer of simian immunodeficiency virus by macaque dendritic cells is enhanced by DC-SIGN.

Dendritic cells (DCs) are among the first cells encountered by human and simian immunodeficiency virus (HIV and SIV) following mucosal infection. Because these cells efficiently capture and transmit virus to T cells, they may play a major role in mediating HIV and SIV infection. Recently, a C-type lectin protein present on DCs, DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN), was shown to efficiently bind and present HIV and SIV to CD4(+), coreceptor-positive cells in trans. However, the significance of DC-SIGN for virus transmission and pathogenesis in vivo remains unclear. Because SIV infection of macaques may represent the best model to study the importance of DC-SIGN in HIV infection, we cloned and characterized pig-tailed macaque DC-SIGN and generated monoclonal antibodies (MAbs) against it. We demonstrate that, like human DC-SIGN, pig-tailed macaque DC-SIGN (ptDC-SIGN) is expressed on DCs and macrophages but not on monocytes, T cells, or B cells. Moderate levels of ptDC-SIGN expression were detected on the surface of DCs, and low-level expression was found on macrophages. Additionally, we show that ptDC-SIGN efficiently binds and transmits replication-competent SIVmne variants to CD4(+), coreceptor-positive cells. Moreover, transmission of virus between pig-tailed macaque DCs and CD4(+) T cells is largely ptDC-SIGN dependent. Interestingly, MAbs directed against ptDC-SIGN vary in the capacity to block transmission of different SIVmne variants. These data demonstrate that ptDC-SIGN plays a central role in transmitting virus from macaque DCs to T cells, and they suggest that SIVmne variants may differ in their interactions with ptDC-SIGN. Thus, SIVmne infection of pig-tailed macaques may provide an opportunity to investigate the significance of DC-SIGN in primate lentiviral infections.

Highly pathogenic simian immunodeficiency virus mne variants that emerge during the course of infection evolve enhanced infectivity and the ability to downregulate CD4 but not class I major histocompatibility complex antigens.

The replicative, cytopathic, and antigenic properties of simian immunodeficiency virus (SIV) variants influence its replication efficiency in vivo. To further define the viral properties and determinants that may be important for high-level replication in vivo and progression to AIDS, we compared a minimally pathogenic SIVmne molecular clone with two highly pathogenic variants cloned from late stages of infection. Both variants had evolved greater infectivity than the parental clone due to mutations in nef. Interestingly, a pol determinant in one of the highly pathogenic variants also contributed to its increased infectivity. Furthermore, because replication in vivo may also be influenced by the ability of a virus to evade the cellular immune response of the host, we examined whether the variants were more capable of downregulating surface expression of class I major histocompatibility complex (MHC). Decreased MHC class I expression was not observed in cells infected with any of the viruses. Furthermore, the Nef proteins of the highly pathogenic variants only slightly reduced surface MHC class I expression in transfected cells, although they efficiently downregulated CD4. Together, these data demonstrate that mutations which can enhance viral infectivity, as well as CD4 downregulation, may be important for efficient replication of SIV in the host. However, Nef-mediated reduction of MHC class I expression does not appear to be critical for the increased in vivo replicative ability of highly pathogenic late variants.