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M-CSF increased Siglec-1 expression on macrophages, rendering them more permissive to HIV-1 infection due to interaction with V1V2 region of gp120 and associated sialic acids., Monocytes and monocyte–derived macrophages express relatively low levels of CD4. Despite this, macrophages can be effectively infected with human immunodeficiency virus type 1. Macrophages have a critical role in human immunodeficiency virus type 1 transmission; however, the mechanism or mechanisms of virus infection are poorly understood. We report that growth factors, such as granulocyte macrophage colony-stimulating factor and macrophage colony-stimulating factor affect the phenotypic profile and permissiveness of macrophages to human immunodeficiency virus type 1. Human immunodeficiency virus type 1 infection of monocyte–derived macrophages derived from granulocyte macrophage and macrophage colony-stimulating factors was predominantly facilitated by the sialic acid-binding immunoglobulin-like lectin-1. The number of sialic acid-binding immunoglobulin-like lectin receptors on macrophage colony-stimulating factor–derived monocyte–derived macrophages was significantly greater than on granulocyte macrophage colony-stimulating factor–derived monocyte–derived macrophages, and correspondingly, human immunodeficiency virus type 1 infection was greater in the macrophage colony-stimulating factor–derived monocyte–derived macrophages. Single-genome analysis and quantitative reverse transcriptase-polymerase chain reaction revealed that the differences in infectivity was not due to differences in viral fitness or in viral variants with differential infectivity but was due to reduced viral entry into the granulocyte macrophage colony-stimulating factor–derived monocyte–derived macrophages. Anti-sialic acid-binding immunoglobulin-like lectin, trimeric glycoprotein 145, and scaffolded V1V2 proteins were bound to sialic acid-binding immunoglobulin-like lectin and significantly reduced human immunodeficiency virus type 1 entry and infection. Furthermore, sialic acid residues present in the V1V2 region of the envelope protein mediated human immunodeficiency virus type 1 interaction with sialic acid-binding immunoglobulin-like lectin and entry into macrophage colony-stimulating factor–derived monocyte–derived macrophages. Removal of sialic acid residues or glycans from scaffolded V1V2 protein decreased human immunodeficiency virus type 1 infectivity. These results highlight the importance of sialic acids on the V1V2 region in binding to sialic acid-binding immunoglobulin-like lectin and suggest that the unusually long surface-exposed sialic acid-binding immunoglobulin-like lectin might aid in the capture and entry of human immunodeficiency virus type 1 into monocyte–derived macrophages.

Background: HIV-1 envelope trimer is a candidate for designing an effective HIV vaccine. Results: gp140 attached to Strep-tag through a long linker is used to purify HIV trimers. Cleaved, uncleaved, and fully and partially glycosylated trimers are characterized. Conclusion: Cleaved and glycosylated gp140 assembles into authentic propeller-shaped trimers. Significance: This system could generate HIV-1 trimers for clinical trials and vaccine manufacture., The trimeric envelope spike of HIV-1 mediates virus entry into human cells. The exposed part of the trimer, gp140, consists of two noncovalently associated subunits, gp120 and gp41 ectodomain. A recombinant vaccine that mimics the native trimer might elicit entry-blocking antibodies and prevent virus infection. However, preparation of authentic HIV-1 trimers has been challenging. Recently, an affinity column containing the broadly neutralizing antibody 2G12 has been used to capture recombinant gp140 and prepare trimers from clade A BG505 that naturally produces stable trimers. However, this antibody-based approach may not be as effective for the diverse HIV-1 strains with different epitope signatures. Here, we report a new and simple approach to produce HIV-1 envelope trimers. The C terminus of gp140 was attached to Strep-tag II with a long linker separating the tag from the massive trimer base and glycan shield. This allowed capture of nearly homogeneous gp140 directly from the culture medium. Cleaved, uncleaved, and fully or partially glycosylated trimers from different clade viruses were produced. Extensive biochemical characterizations showed that cleavage of gp140 was not essential for trimerization, but it triggered a conformational change that channels trimers into correct glycosylation pathways, generating compact three-blade propeller-shaped trimers. Uncleaved trimers entered aberrant pathways, resulting in hyperglycosylation, nonspecific cross-linking, and conformational heterogeneity. Even the cleaved trimers showed microheterogeneity in gp41 glycosylation. These studies established a broadly applicable HIV-1 trimer production system as well as generating new insights into their assembly and maturation that collectively bear on the HIV-1 vaccine design.

The α4s7 integrin present on host cells recognizes the V1V2 domain of the HIV-1 envelope protein. This interaction might be involved in virus transmission. Administration of α4s7-specific antibodies inhibit acquisition of SIV in a macaque challenge model. But the molecular details of V1V2: α4s7 interaction are unknown and its importance in HIV-1 infection remains controversial. Our biochemical and mutational analyses show that glycosylation is a key modulator of V1V2 conformation and binding to α4s7. Partially glycosylated, but not fully glycosylated, envelope proteins are preferred substrates for α4s7 binding. Surprisingly, monomers of the envelope protein bound strongly to α4s7 whereas trimers bound poorly. Our results suggest that a conformationally flexible V1V2 domain allows binding of the HIV-1 virion to the α4s7 integrin, which might impart selectivity for the poorly glycosylated HIV-1 envelope containing monomers to be more efficiently captured by α4s7 integrin present on mucosal cells at the time of HIV-1 transmission.