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Placental Hofbauer cells assemble and sequester HIV-1 in tetraspanin-positive compartments that are accessible to broadly neutralizing antibodies.

Johnson EL, Chu H, Byrareddy SN, Spearman P, Chakraborty R - J Int AIDS Soc (2015)

Bottom Line: Following infection, we observed HIV-1 accumulation in potentially acidic compartments, which stained intensely with Lysotracker-Red.Remarkably, these compartments are readily accessible via the cell surface and can be targeted by exogenously applied small molecules and HIV-1-specific broadly neutralizing antibodies.In addition, broadly neutralizing antibodies (4E10 and VRC01) limited viral replication by HIV-1-infected HCs, which may be mediated by FcγRI.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA.

ABSTRACT

Introduction: Within monocyte-derived macrophages, HIV-1 accumulates in intracellular virus-containing compartments (VCCs) that are inaccessible to the external environment, which implicate these cells as latently infected HIV-1 reservoirs. During mother-to-child transmission of HIV-1, human placental macrophages (Hofbauer cells (HCs)) are viral targets, and have been shown to be infected in vivo and sustain low levels of viral replication in vitro; however, the risk of in utero transmission is less than 7%. The role of these primary macrophages as viral reservoirs is largely undefined. The objective of this study is to define potential sites of viral assembly, accumulation and neutralization in HCs given the pivotal role of the placenta in preventing HIV-1 infection in the mother-infant dyad.

Methods: Term placentae from 20 HIV-1 seronegative women were obtained following caesarian section. VCCs were evaluated by 3D confocal and electron microscopy. Colocalization R values (Pearson's correlation) were quantified with colocalization module of Volocity 5.2.1. Replication kinetics and neutralization studies were evaluated using p24 ELISA.

Results: We demonstrate that primary HCs assemble and sequester HIV-1(BaL) in intracellular VCCs, which are enriched in endosomal/lysosomal markers, including CD9, CD81, CD63 and LAMP-1. Following infection, we observed HIV-1 accumulation in potentially acidic compartments, which stained intensely with Lysotracker-Red. Remarkably, these compartments are readily accessible via the cell surface and can be targeted by exogenously applied small molecules and HIV-1-specific broadly neutralizing antibodies. In addition, broadly neutralizing antibodies (4E10 and VRC01) limited viral replication by HIV-1-infected HCs, which may be mediated by FcγRI.

Conclusions: These findings suggest that placental HCs possess intrinsic adaptations facilitating unique sequestration of HIV-1, and may serve as a protective viral reservoir to permit viral neutralization and/or antiretroviral drug entry in utero.

No MeSH data available.


Related in: MedlinePlus

Electron microscopy of HIV-1 infected HCs reveals viral budding at plasma membrane and within intracellular compartments. HIV-1BaL infected HCs were fixed and analyzed by standard electron microscope processing procedures five days post-infection. Sections show intracellular virus-containing compartments (VCCs) with mature virions (red asterisk, a–h), budding profiles (solid arrows, c–e, i) and immature virions (open arrows, b). Mature viral particles were seen under folds (f and h) of the plasma membrane (PM) and in the extracellular space adjacent to the PM (g). Virus budding profiles were observed on the PM (i). Bars represent 0.6 µm for a, b, e and g; 1.5 µm for c and f; 0.6 µm for d and h; and 0.3 µm for i. Sections shown represent a minimum of 20 cells for each condition from four donors.
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Figure 0003: Electron microscopy of HIV-1 infected HCs reveals viral budding at plasma membrane and within intracellular compartments. HIV-1BaL infected HCs were fixed and analyzed by standard electron microscope processing procedures five days post-infection. Sections show intracellular virus-containing compartments (VCCs) with mature virions (red asterisk, a–h), budding profiles (solid arrows, c–e, i) and immature virions (open arrows, b). Mature viral particles were seen under folds (f and h) of the plasma membrane (PM) and in the extracellular space adjacent to the PM (g). Virus budding profiles were observed on the PM (i). Bars represent 0.6 µm for a, b, e and g; 1.5 µm for c and f; 0.6 µm for d and h; and 0.3 µm for i. Sections shown represent a minimum of 20 cells for each condition from four donors.

Mentions: In T cells and several non-hematopoietic cell lines, the majority of virus particles assemble at the cell surface, but in primary MDMs these events occur almost entirely in intracellular VCCs [10,26]. HCs infected with HIV-1BaL for five days were fixed for transmission electron microscopy (Figure 3). The cells were infected for a longer time period to increase intracellular viral stores. Accumulation of mature HIV-1 virions was readily detected within intracellular VCCs throughout the cytoplasm, near the plasma membrane and in the extracellular space adjacent to the plasma membrane. Early-/late-budding viral particles were frequently detected within the VCCs and on the plasma membrane, suggesting that HIV-1 virions are assembled in these compartments.


Placental Hofbauer cells assemble and sequester HIV-1 in tetraspanin-positive compartments that are accessible to broadly neutralizing antibodies.

Johnson EL, Chu H, Byrareddy SN, Spearman P, Chakraborty R - J Int AIDS Soc (2015)

Electron microscopy of HIV-1 infected HCs reveals viral budding at plasma membrane and within intracellular compartments. HIV-1BaL infected HCs were fixed and analyzed by standard electron microscope processing procedures five days post-infection. Sections show intracellular virus-containing compartments (VCCs) with mature virions (red asterisk, a–h), budding profiles (solid arrows, c–e, i) and immature virions (open arrows, b). Mature viral particles were seen under folds (f and h) of the plasma membrane (PM) and in the extracellular space adjacent to the PM (g). Virus budding profiles were observed on the PM (i). Bars represent 0.6 µm for a, b, e and g; 1.5 µm for c and f; 0.6 µm for d and h; and 0.3 µm for i. Sections shown represent a minimum of 20 cells for each condition from four donors.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308659&req=5

Figure 0003: Electron microscopy of HIV-1 infected HCs reveals viral budding at plasma membrane and within intracellular compartments. HIV-1BaL infected HCs were fixed and analyzed by standard electron microscope processing procedures five days post-infection. Sections show intracellular virus-containing compartments (VCCs) with mature virions (red asterisk, a–h), budding profiles (solid arrows, c–e, i) and immature virions (open arrows, b). Mature viral particles were seen under folds (f and h) of the plasma membrane (PM) and in the extracellular space adjacent to the PM (g). Virus budding profiles were observed on the PM (i). Bars represent 0.6 µm for a, b, e and g; 1.5 µm for c and f; 0.6 µm for d and h; and 0.3 µm for i. Sections shown represent a minimum of 20 cells for each condition from four donors.
Mentions: In T cells and several non-hematopoietic cell lines, the majority of virus particles assemble at the cell surface, but in primary MDMs these events occur almost entirely in intracellular VCCs [10,26]. HCs infected with HIV-1BaL for five days were fixed for transmission electron microscopy (Figure 3). The cells were infected for a longer time period to increase intracellular viral stores. Accumulation of mature HIV-1 virions was readily detected within intracellular VCCs throughout the cytoplasm, near the plasma membrane and in the extracellular space adjacent to the plasma membrane. Early-/late-budding viral particles were frequently detected within the VCCs and on the plasma membrane, suggesting that HIV-1 virions are assembled in these compartments.

Bottom Line: Following infection, we observed HIV-1 accumulation in potentially acidic compartments, which stained intensely with Lysotracker-Red.Remarkably, these compartments are readily accessible via the cell surface and can be targeted by exogenously applied small molecules and HIV-1-specific broadly neutralizing antibodies.In addition, broadly neutralizing antibodies (4E10 and VRC01) limited viral replication by HIV-1-infected HCs, which may be mediated by FcγRI.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA.

ABSTRACT

Introduction: Within monocyte-derived macrophages, HIV-1 accumulates in intracellular virus-containing compartments (VCCs) that are inaccessible to the external environment, which implicate these cells as latently infected HIV-1 reservoirs. During mother-to-child transmission of HIV-1, human placental macrophages (Hofbauer cells (HCs)) are viral targets, and have been shown to be infected in vivo and sustain low levels of viral replication in vitro; however, the risk of in utero transmission is less than 7%. The role of these primary macrophages as viral reservoirs is largely undefined. The objective of this study is to define potential sites of viral assembly, accumulation and neutralization in HCs given the pivotal role of the placenta in preventing HIV-1 infection in the mother-infant dyad.

Methods: Term placentae from 20 HIV-1 seronegative women were obtained following caesarian section. VCCs were evaluated by 3D confocal and electron microscopy. Colocalization R values (Pearson's correlation) were quantified with colocalization module of Volocity 5.2.1. Replication kinetics and neutralization studies were evaluated using p24 ELISA.

Results: We demonstrate that primary HCs assemble and sequester HIV-1(BaL) in intracellular VCCs, which are enriched in endosomal/lysosomal markers, including CD9, CD81, CD63 and LAMP-1. Following infection, we observed HIV-1 accumulation in potentially acidic compartments, which stained intensely with Lysotracker-Red. Remarkably, these compartments are readily accessible via the cell surface and can be targeted by exogenously applied small molecules and HIV-1-specific broadly neutralizing antibodies. In addition, broadly neutralizing antibodies (4E10 and VRC01) limited viral replication by HIV-1-infected HCs, which may be mediated by FcγRI.

Conclusions: These findings suggest that placental HCs possess intrinsic adaptations facilitating unique sequestration of HIV-1, and may serve as a protective viral reservoir to permit viral neutralization and/or antiretroviral drug entry in utero.

No MeSH data available.


Related in: MedlinePlus