Human immunodeficiency virus-1 (HIV-1) is primarily transmitted sexually. Dendritic cells (DCs) in the subepithelium transmit HIV-1 to T cells through the C-type lectin DC-specific intercellular adhesion molecule (ICAM)-3-grabbing nonintegrin (DC-SIGN). However, the epithelial Langerhans cells (LCs) are the first DC subset to encounter HIV-1. It has generally been assumed that LCs mediate the transmission of HIV-1 to T cells through the C-type lectin Langerin, similarly to transmission by DC-SIGN on dendritic cells (DCs). Here we show that in stark contrast to DC-SIGN, Langerin prevents HIV-1 transmission by LCs. HIV-1 captured by Langerin was internalized into Birbeck granules and degraded. Langerin inhibited LC infection and this mechanism kept LCs refractory to HIV-1 transmission; inhibition of Langerin allowed LC infection and subsequent HIV-1 transmission. Notably, LCs also inhibited T-cell infection by viral clearance through Langerin. Thus Langerin is a natural barrier to HIV-1 infection, and strategies to combat infection must enhance, preserve or, at the very least, not interfere with Langerin expression and function.

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Protein folding in the endoplasmic reticulum goes hand in hand with disulfide bond formation, and disulfide bonds are considered key structural elements for a protein's folding and function. We used the HIV-1 Envelope glycoprotein to examine in detail the importance of its 10 completely conserved disulfide bonds. We systematically mutated the cysteines in its ectodomain, assayed the mutants for oxidative folding, transport, and incorporation into the virus, and tested fitness of mutant viruses. We found that the protein was remarkably tolerant toward manipulation of its disulfide-bonded structure. Five of 10 disulfide bonds were dispensable for folding. Two of these were even expendable for viral replication in cell culture, indicating that the relevance of these disulfide bonds becomes manifest only during natural infection. Our findings refine old paradigms on the importance of disulfide bonds for proteins.

We studied human immunodeficiency virus type 1 (HIV-1) chimeric viruses altering in their gp120 V1V2 and V3 envelope regions to better map which genetic alterations are associated with specific virus phenotypes associated with HIV-1 disease progression. The V1V2 and V3 regions studied were based on viruses isolated from an individual with progressing HIV-1 disease. Higher V3 charges were linked with CXCR4 usage, but only when considered within a specific V1V2 and V3 N-linked glycosylation context. When the virus gained R5X4 dual tropism, irrespective of its V3 charge, it became highly resistant to inhibition by RANTES and highly sensitive to inhibition by SDF-1␣. R5 viruses with higher positive V3 charges were more sensitive to inhibition by RANTES, while R5X4 dualtropic viruses with higher positive V3 charges were more resistant to inhibition by SDF-1␣. Loss of the V3 N-linked glycosylation event rendered the virus more resistant to inhibition by SDF-1␣. The same alterations in the V1V2 and V3 regions influenced the extent to which the viruses were neutralized with soluble CD4, as well as monoclonal antibodies b12 and 2G12, but not monoclonal antibody 2F5. These results further identify a complex set of alterations within the V1V2 and V3 regions of HIV-1 that can be selected in the host via alterations of coreceptor usage, CC/CXC chemokine inhibition, CD4 binding, and antibody neutralization.Human immunodeficiency virus type 1 (HIV-1) belongs to the family of lentiviruses that cause slow degenerative diseases (16,17, 36). The high rate of mutation associated with HIV-1 allows for the generation of viruses that can evade the host immune responses and that give rise to variant biological properties, such as cell tropism. HIV-1 predominantly enters the cell types that it infects through an initial interaction between the gp120 envelope of the virus and the CD4 molecule, followed by an interaction with a specific CC/CXC chemokine receptor, thereby mediating membrane fusion and viral entry (3,42). Although a multitude of coreceptors can be utilized by HIV-1, the two most significant for virus transmission and pathogenesis are the CC chemokine receptor CCR5 and the CXC chemokine receptor CXCR4, respectively (2, 57). The preferred phenotypic classifications for HIV-1 are R5 for isolates using CCR5, X4 for those using CXCR4, and R5X4 for those capable of using both coreceptors (3). The association of X4 variants with disease progression and the maintenance of R5 variants throughout infection suggest that X4 viruses are either a cause of or evolve in response to progressive immunosuppression, while R5 variants make up the reservoir responsible for persistent infection (45,46,48,52). Detection of X4 viruses is also predictive of rapid CD4 cell decline (9, 28).Although X4 isolates can occasionally be detected early, they usually appear later in infection and are associated with progression to AIDS (10, 49).The CC chemokines RANTES, MIP-1␣, and MIP-1␤, the natural ligands for the CCR5 chemokine receptor, and SDF-1␣, the na...