Macrophage infection via selective capture of HIV-1-infected CD4+ T cells

Abstract

Macrophages contribute to HIV-1 pathogenesis by forming a viral reservoir and mediating neurological disorders. Cell-free HIV-1 infection of macrophages is inefficient, in part due to low plasma membrane expression of viral entry receptors. We find that macrophages selectively capture and engulf HIV-1-infected CD4+ T cells leading to efficient macrophage infection. Infected T cells, both healthy and dead or dying, were taken up through viral envelope glycoprotein-receptor-independent interactions, implying a mechanism distinct from conventional virological synapse formation. Macrophages infected by this cell-to-cell route were highly permissive for both CCR5-using macrophage-tropic and otherwise weakly macrophage-tropic transmitted/founder viruses but restrictive for nonmacrophage-tropic CXCR4-using virus. These results have implications for establishment of the macrophage reservoir and HIV-1 dissemination in vivo.

Graphical abstract

Figure 1

Macrophages Capture and Engulf HIV-1-Infected T Cells (A) Time-lapse sequence of HIV-1-_NL4.3-GFP-infected Jurkats mixed with MDM. Infected T cells are labeled 1, 2, and 3 in the engulfment order. Scale bar 10 μm. Time shown as hh:mm:ss. See Movies S1, S2, and S3. (B) Experimental strategy for isolation, infection, coculture, and analysis of primary donor cells. (C) ImageStream images of pre-coculture primary HIV-1⁺ CD4⁺ T cells selected for focus, size, and aspect ratio labeled for the phenotypes analyzed: CD3 (T cells, blue), Gag (green), Caspase3 (early apoptosis, red), or live/dead (LD, late apoptosis/necrosis, orange), and all channels merged with and without brightfield (BF). (D) ImageStream images of MDMs associated with T cells selected for focus, MDMs based on size and aspect ratio, then CD3⁺ labeling from 5 × 10⁴ total acquired events showing single engulfed T cells labeled for the different phenotypes analyzed. (E) Summary of data quantified from 10³ images such as those in (C) and (D) counted for engulfed T cell phenotype (each circle represents one donor, nine independent donors, three independent experiments). Percentages of MDM containing different subsets of T cells were calculated and expressed as an index based upon the frequency of each T cell subset prior to MDM uptake relative to the frequency after uptake. The third and fourth categories (CD3⁺/dead/dying and CD3⁺/Gag⁺/dead/dying) combine independent experiments reporting markers of cell death: Caspase3 and LD (red) or PS (blue). Statistical analysis using Kruskal-Wallis one-way ANOVA with Dunn’s multiple comparison post hoc test. ^∗p < 0.05; ^∗∗p < 0.01; ^∗∗∗p < 0.001. See Figure S1.

Figure 2

Interactions Implicated in MDM Capture of HIV-1-Infected T Cells (A) Short-term MDM uptake assay of HIV-1_BaL⁺ primary T cells via direct contact (cell-to-cell, CTC, red), across transwells (TW, black), or HIV-1_Bal T cell supernatants added directly to MDM (cell-free, CF, white). Uptake was measured by qPCR for MDM-associated pol vDNA, normalized to β-globin copy number and to cell-cell transfer at 1 hr = 1. Bars = mean relative HIV-1 DNA copies for five donors + SEM, each donor analyzed in triplicate. ^∗∗p < 0.01; ^∗∗∗p < 0.001 by Kruskal-Wallis one-way ANOVA with Dunn’s multiple comparison post hoc test comparing all to CTC T = 0.25. See Figures S2A–S2C. (B) Inhibition of MDM uptake of HIV-1_BaL⁺ primary T cells. MDMs (Jasp, EIPA, 13B8.2, Tak779, and T20) or HIV-1_BaL⁺ T cells (2G12, sCD4, and T20) were pretreated for 1 hr with saturating concentrations of inhibitors, cocultured for 30 min, washed to remove unattached T cells, DNA extracted, and qPCR for pol vDNA and β-globin performed. Bars = mean uptake inhibition (%) for each treatment normalized to appropriate controls + SEM for 4 to 13 independent donors, each analyzed in triplicate. ^∗∗p < 0.01; ^∗∗∗p < 0.001 by one-sample t test comparing each treatment to a hypothetical value of 0 (no inhibition) with Sidak’s multiple comparison post hoc test. See Figures S2D–S2F, S3B, and S4. (C and D) Env is not required for HIV-1⁺ T cell uptake. CD4⁺ T cells were synchronously infected for 48 hr with HIV-1_BaL or VSV-G pseudotyped HIV-1_BaLΔEnv and cultured 1:1 with autologous MDM for 3 hr. MDMs were washed lifted, fixed, permeabilized, and analyzed for intracellular CD3 and Gag by flow cytometry. Bars equal normalized mean of flow cytometry data from two independent donors each analyzed in triplicate + SEM. (C) Percentage Gag⁺ CD4⁺ T cells (blue bars) and MDMs (black bars). (D) Normalized uptake of Gag⁺MDM/Gag⁺ T cells (% Gag⁺ MDM / % Gag⁺ T cells). Bars = normalized mean of flow cytometry data from two independent donors each analyzed in triplicate. ns = p > 0.05, Mann-Whitney U. See Figures S3D and S3E.

Figure 3

MDM Are Efficiently Infected by HIV-1⁺ T Cells (A) MDM infection by capture of HIV-1⁺ T cells. HIV-1_BaL⁺ primary T cells were cocultured with MDMs for 3 hr, T cells washed off, and MDMs cultured ± AZT for the times shown prior to lysis and qPCR for HIV-1 pol product normalized to β-globin copy number. Data represent mean relative HIV-1 vDNA copies from four independent donors + SEM. ^∗p < 0.05, as determined by Kruskal-Wallis one-way ANOVA with Dunn’s multiple comparison post hoc test, normalized to T = 0 + AZT. (B) HIV-1_BaL-infected primary CD4⁺ T cells directly cocultured with autologous MDM (CTC) or separated by virus-permeable transwell (TW) membranes for the times shown were washed, further cultured, and supernatant Gag assayed. Results are means of experimental quadruplicates+ SEM from an experiment representative of three independent experiments each with an independent donor. See Figures S2A–S2C. (C) HIV-1_BaL-GFP⁺ primary T cells were cocultured for 6 hr with autologous MDMs; extensively washed; and MDMs were cultured for 3 days, fixed, permeabilized, and prepared for confocal microscopy. Each image represents a single optical x-y section, cells labeled for CD3 (red) and nuclei (blue). Scale bars = 20 μm. Top panel, MDM exposed to cell-free HIV-1_BaL-GFP through 3 μm transwell membranes; middle panel: MDM + AZT prior to and during coculture with HIV-1_BaL-GFP⁺ T cells; bottom panel: MDMs directly cocultured with HIV-1_BaL-GFP⁺ T cells. (D) Quantification from images represented in (C). MDMs under each condition were quantified for GFP expression, and data was expressed as means of + SEM of n = 500 MDMs in five randomly selected fields from four independent donors. ^∗p < 0.05 Kruskal-Wallis one-way ANOVA with Dunn’s multiple comparison post hoc test. (E) Jasplakinolide inhibits HIV-1⁺ T-cell-mediated, but not cell-free, infection of MDMs. Jasplakinolide (Jasp, 5 μM) was added to MDMs for 1 hr prior to washing and direct coculture with HIV-1_Bal⁺ T cells (CTC, red) or their supernatants (CF, black). Infection was measured by supernatant Gag levels 3 days post-coculture. Bars = mean inhibition of infection (%) + SEM for four independent donors, each in triplicate. ^∗∗∗p < 0.001 by one-sample t test, comparing each condition to a hypothetical value of 0 with Sidak’s multiple comparison post hoc test. See Figure S2. (F) HIV-1 entry inhibitors block MDM infection. MDMs were cocultured with autologous HIV-1_BaL⁺ T cells for 3 hr, washed extensively to remove unattached T cells, and cultured with entry inhibitors for 14 days with Gag release assayed every 2 days. Bars = AUC analysis normalized to no drug controls and expressed as inhibition of infection (%) + SEM for four donors, each in triplicate. ^∗p < 0.05, ^∗∗p < 0.01 by one-sample t test, comparing each condition to a hypothetical value of 0 with Sidak’s multiple comparison post hoc test. See Figure S3. (G) MDMs derived from a Δ32 CCR5 homozygous donor are resistant to infection by HIV-1⁺ T capture. MDMs from five CCR5 WT donors or a Δ32 CCR5 homozygote were cocultured with heterologous HIV-1_BaL-Luc⁺ T cells for 6 hr, washed, and cultured for a further 3 days prior to lysis and measurement of luciferase activity. Bars equal means of quadruplicates + SEM. ^∗p < 0.05 Mann Whitney U. See Figure S5A. (H and I) MDM infection by HIV-1⁺ T cell capture results in release of infectious virus. MDMs from four independent donors were cocultured with HIV-1_BaL-Luc⁺ T cells directly or across a transwell (TW) for 6 hr prior to washing and further culture ± AZT for 3 days. (H) Supernatants from MDMs without AZT were titrated onto TZM-bl indicator cells and infectious units/ml determined. (I) MDMs washed to remove free virus were cocultured with autologous CD4⁺ T cells ± AZT for 24 hr prior to collection of T cells. T cells were washed and maintained ± AZT for 3 days prior to lysis and luciferase assay. Bars = means + SEM, ^∗p < 0.05 by paired Students t test.

Figure 4

HIV-1⁺ T-Cell-Mediated Infection of MDMs and Viral Tropism (A) NM-tropic HIV-1 does not establish significant infection in MDMs. ImageStream images selected from 5 × 10⁴ total acquired events gated for MDMs. HIV-1_BaL supernatant virus or HIV-1_BaL- or HIV-1_IIIB-infected primary T cells cocultured for 6 hr with autologous MDMs were washed free of unattached T cells, cultured for 6 days, fixed, and processed for ImageStream analysis. Cells were labeled for CD3 (blue) and Gag (green), brightfield = BF. (B) Quantification of data from assay as in (A) showing % MDM containing Gag and corresponding supernatant p24 Gag levels after coculture with HIV-1_BaL⁺ T cells ± 1 hr AZT pretreatment. Where appropriate AZT was maintained in coculture and on MDMs post-coculture for 6 days. Data are from two independent experiments with four independent donors, p24 analyzed in triplicate. Bars = mean % Gag⁺ MDM or p24 (ng/ml) + SEM ^∗p < 0.05 by Mann-Whitney U comparing CTC to AZT for each measure. (C) Summary of data quantified from images such as those in (A). Bars represent % Gag⁺ MDM + SEM from four independent donors, separated into CD3-associated (blue) and non-CD3-associated (red). ^∗p < 0.05 by one-way ANOVA with Bonferroni’s multiple comparison post hoc test comparing total % Gag⁺ MDM between cell-to-cell HIV-1_BaL and HIV-1_IIIB or HIV-1_BaL cell-to cell to HIV-1_BaL cell-free. ^∗∗p < 0.01 by Student’s t test comparing the proportion of CD3-associated (blue) to non-CD3-associated (red) Gag. See Figures S5B–S5D.

Figure 5

T Cell Capture Facilitates T/F Virus Infection of MDM (A) Primary T cells infected individually with IMCs expressing two M-tropic R5 Envs (BaL, YU2) or 6 T/F Envs (CH040, THRO, RHPA, WITO, REJO, and SUMA) (Ochsenbauer et al., 2012) were cultured for 6 hr directly (CTC) or across transwells (TW) with autologous MDMs. Following washing, MDMs were cultured for 6 days, lysed, and luciferase assayed. Results are mean signal + SEM for each individual IMC data set pooled into M-tropic or T/F groups from four independent donors, and values are normalized to % Gag⁺ T cells prior to coculture. ^∗∗p < 0.01 Kruskal-Wallis ANOVA plus Dunn’s multiple comparison post hoc test. See Figure S5E. (B) MDMs were cocultured with HIV-1⁺ T cells as in (A), cultured for 10 days, and supernatant Gag measured and normalized as above. Boxes represent mean normalized Gag ± SEM of four independent donor infections in two independent experiments, each analyzed in triplicate. AUC analysis ^∗∗p < 0.01; ^∗∗∗p < 0.001. (C) MDM cocultured with primary autologous CD4⁺ T cells infected with the IMCs expressing Env from HIV-1_BaL, HIV-1_CH040, or HIV-1_THRO for 7 days were washed to remove T cells cultured for a further 6 days; fixed; and labeled for confocal fluorescence microscopy with anti-CD3 (green) and Gag p17 (red) antibodies. BF = brightfield; scale bars = 20 μm. (D) MDMs were cocultured with T cells infected with the IMCs shown or infected with concentrated cell-free virus at the MOIs shown for 6 hr, cultured for a further 3 days, washed, lysed, and luciferase assayed. Results are mean signal ± SEM for four independent donors. Left panel is cell-free (CF) infection; right panel is cell-to-cell (CTC) infection. (E) MDMs were cocultured with IMC-infected T cells for 3 hr with the inhibitors shown, washed, and cultured for a further 3 days in the continued presence of the inhibitors. MDM, were washed, lysed, and assayed for luciferase activity. Individual datum points = the mean of three to four independent donors from two independent experiments for each virus tested. Lines represent the overall mean for each group (M-tropic or T/F). ^∗p < 0.05; ^∗∗∗p < 0.001 by one-sample t test comparing means to a hypothetical value of 0 (no inhibition) with Sidak’s multiple comparison post hoc test.