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. 2011 May 19;9(5):415-24.
doi: 10.1016/j.chom.2011.04.007.

A nonredundant role for plasmacytoid dendritic cells in host defense against the human fungal pathogen Aspergillus fumigatus

Zaida G Ramirez-Ortiz  1 , Chrono K Lee, Jennifer P Wang, Louis Boon, Charles A Specht, Stuart M Levitz
Affiliations

A nonredundant role for plasmacytoid dendritic cells in host defense against the human fungal pathogen Aspergillus fumigatus

Zaida G Ramirez-Ortiz et al. Cell Host Microbe. .

Abstract

While plasmacytoid dendritic cells (pDCs), a natural type I interferon (IFN)-producing cell type, are regarded as critical for innate immunity to viruses, their role in defense against fungal infections remains unknown. We examined the interactions of pDCs with hyphae of the invasive human fungal pathogen Aspergillus fumigatus. Human pDCs spread over hyphae and inhibited their growth. Antifungal activity was retained in pDC lysates, did not require direct fungal contact, and was partially reversed by zinc. Incubation with hyphae resulted in pDC cytotoxicity, partly due to fungal gliotoxin secretion. Following hyphal stimulation, pDCs released proinflammatory cytokines via a TLR9-independent mechanism. Pulmonary challenge of mice with A. fumigatus resulted in a substantial influx of pDCs into lungs, and pDC-depleted mice were hypersusceptible to invasive aspergillosis. These data demonstrate the antifungal activity of pDCs against A. fumigatus and establish their nonredundant role in host defenses against invasive aspergillosis in vivo.

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Figures

Figure 1
Figure 1. Antimicrobial activity of pDCs against A. fumigatus.
(A) pDCs (5×104) were incubated with the indicated number of A. fumigatus hyphae for 2 hr. Antifungal activity of pDCs was then measured by the XTT assay. Data represent means ± SE from two donors, each tested in duplicate. (B) A. fumigatus hyphae were incubated for the specified times with or without pDCs and hyphal length determined. Data represent means ± SE from two experiments. For each variable, at least 75 hyphal measurements were recorded. p<0.0001, when comparing hyphal lengths in the presence or absence of pDCs at the 2 and 4 hr time points. (C) pDCs (1×105) were incubated with A. fumigatus (1×105) at 37°C for 2 hr. After fixation, pDCs were stained with anti-CD123-efluor650 (red) and A. fumigatus hyphae were stained with Uvitex (green). Samples were analyzed by confocal microscopy. Arrowheads point to two swollen conidia phagocytosed by a pDC. Arrows point to a hypha which is covered by a pDC. The photomicrographs depicted are representative of three independent experiments with similar results.
Figure 2
Figure 2. A. fumigatus hyphae lyse pDCs but pDC lysates have antifungal activity.
(A) The indicated number of pDCs was incubated with or without 3×104 A. fumigatus hyphae for 2 hr. Supernatants were then collected and cytotoxicity of pDC was assessed by LDH release. Data represent means ± SE of three donors, each studied in triplicate. p< 0.0001 when comparing cytotoxicity with and without hyphae for each concentration of pDCs. (B) A. fumigatus hyphae were incubated with live pDCs or lysates obtained from the indicated number of pDCs. Antifungal activity was measured by the XTT assay. Data represent means ± SE of three donors, each studied in triplicate. No significant differences were observed comparing pDC lysates with live pDCs at any of the cell concentrations studied. (C) A. fumigatus hyphae were incubated with or without pDCs (5×104) in the presence or absence of 10 μM ZnCl2 or 10 μM FeCl3. At the specified times, hyphal length was measured as described in Methods. Solid lines represent A. fumigatus alone whereas dotted lines represent A. fumigatus incubated with pDCs. Data represent means ± SE of two individual experiments. p<0.001 comparing fungal growth in the presence or absence of pDCs. (D) pDCs were hypotonically lysed and 100 μg of total protein were analyzed by Western blot using a monoclonal antibody against human calprotectin. Blot is representative of 3 separate experiments. Lines point to where the indicated molecular size standards (in kD) ran on the gel. (E) The antifungal activity of pDC lysates was determined before and after immunodepletion of calprotectin. Data are from three donors, each studied in triplicate. p<0.001 comparing lysates with and without immunodepletion.
Figure 3
Figure 3. Influence of cell contact on pDC cytotoxicity and antifungal activity.
(A) A. fumigatus hyphae (5×104) were grown on the bottom of wells containing a permeable insert (Transwell) with a size exclusion limit of 0.4 μm. pDCs (5×104) were then added either to the top of the insert (No Contact) or below the insert (Contact). After a 2 hr incubation, supernatants were collected and pDC cytotoxicity was measured by LDH assay. p<0.0001, when comparing pDCs in the presence or absence of A. fumigatus for both the “No Contact” and “Contact” groups. (B) As in part A, except antifungal activity was measured by the XTT assay. In addition, the antifungal activity of lysates from 5×104 pDCs was assayed. p< 0.0001, when comparing any two groups except “Contact” and “Lysates”. For parts A and B, data represent means ± SE from four donors, each tested in triplicate.
Figure 4
Figure 4. Role of gliotoxin and other A. fumigatus secondary metabolites in the induction of pDC death.
(A) pDCs (5×104) were treated with the indicated concentrations of gliotoxin. After a 2 hr incubation, supernatants were collected and cell mediated cytotoxicity was measured by LDH assay. Data represent means ± SE from four donors, each tested in duplicate. (B, C) pDCs (5×104) were left unstimulated (Unstim) or incubated for 2 hr with hyphae (5×104) from the indicated strain of A. fumigatus (see Supplemental Table 1). pDC cytotoxicity and antifungal activity were analyzed by LDH and XTT assays, respectively. Data represent means ± SE of duplicate experiments from separate donors, each of which was performed in triplicate. p<0.0001, when comparing deletion strains with their complemented counterparts as well as wild-type A. fumigatus (Af293).
Figure 5
Figure 5. Mechanism of pDC death.
pDCs (1×105) were left unstimulated (Unstim) or stimulated for 2 hr with either A. fumigatus (Af293, 1×105) hyphae or gliotoxin (20 ng/mL). Following incubation, samples were fixed and stained for DNA fragmentation by TUNEL (Alexa Fluor 594) and total DNA (Hoechst 33342). Cells were then examined by confocal microscopy. (A) TUNEL positivity was determined for at least 100 pDCs per group. Data represent means ± SE of two individual experiments performed in duplicate; p<0.01, when comparing unstimulated with A. fumigatus or gliotoxin. (B) Representative confocal microscopy images.
Figure 6
Figure 6. Cytokine release by pDCs stimulated with A. fumigatus hyphae.
(A) and (B). PBMC were separated into pDC positive (pDCs) and negative (Flow Through) fractions using CD304-coated magnetic beads. The pDCs and flow through cells (5×104/well) were then left unstimulated (Unstim) or stimulated for 6 hr with A. fumigatus hyphae (5×104), CpG (100 ng/mL) or LPS (10 ng/mL). Supernatants were analyzed by ELISA for IFNα (A) and TNFα (B). Data represent means ± SE of cytokine concentrations from two donors, each analyzed in duplicate. p<0.0001 comparing cytokine secretion by unstimulated cells with any stimulus except for unstimulated pDCs compared with LPS-stimulated pDCs. (C) pDCs (5×104) were pretreated for 60 min with 10 μg/mL chloroquine (Chl), 10 μg/mL of bafilomycin A1 (BafA), or left untreated prior to 6 hr stimulation with A. fumigatus hyphae (5×104), CpG (100 ng/mL) or LPS (10 ng/mL). Supernatants were analyzed by ELISA for IFNα. Data represent means ± SE of cytokine concentrations from two donors, each analyzed in triplicate. p<0.0001, when comparing unstimulated pDCs to pDCs incubated with A. fumigatus or CpG. IFNα levels stimulated by A. fumigatus were not significantly affected by treatment with BafA or Chl.
Figure 7
Figure 7. Contribution of pDCs to defenses against invasive aspergillosis.
Mice were infected with A. fumigatus conidia via pulmonary (A) or intravenous (B and C) challenge and followed 30 days for survival. (A and B) Mice were treated with the antibodies 120G8 (pDC-depleted) or GL113 (Control), as described in Methods, but did not receive any other immunosuppression. (C) Susceptibility of IFNα/βR−/− and wild-type mice to aspergillosis was compared. Data from A, B and C represent combined survival curves of 2 independent experiments, each with similar results. The number (N) of mice per group is indicated in the figure inset. p<0.0001 when comparing survival of pDC depleted mice vs control antibody treated mice. p<0.003 when comparing survival of IFNα/βR−/− mice to WT mice. (D) Wild-type mice were left untreated (Control) or given 120G8 (pDC-depleted). Mice were then either left uninfected or infected via the pulmonary route with A. fumigatus. After 48 hr, the number of pDCs in the lungs was determined. Data represent means +/− SEM of two experiments, each with 3 - 5 mice per group. p<0.0001 comparing the total number of pDC of uninfected or depleted mice to the total number of pDCs of untreated/infected group.
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