Plasmacytoid dendritic cell ablation impacts early interferon responses and antiviral NK and CD8(+) T cell accrual

Abstract

Plasmacytoid dendritic cells (pDCs) mediate type I interferon (IFN-I) responses to viruses that are recognized through the Toll-like receptor 7 (TLR7) or TLR9 signaling pathway. However, it is unclear how pDCs regulate the antiviral responses via innate and adaptive immune cells. We generated diphtheria toxin receptor transgenic mice to selectively deplete pDCs by administration of diphtheria toxin. pDC-depleted mice were challenged with viruses known to activate pDCs. In murine cytomegalovirus (MCMV) infection, pDC depletion reduced early IFN-I production and augmented viral burden facilitating the expansion of natural killer (NK) cells expressing the MCMV-specific receptor Ly49H. During vesicular stomatitis virus (VSV) infection, pDC depletion enhanced early viral replication and impaired the survival and accumulation of virus-specific cytotoxic T lymphocytes. We conclude that pDCs mediate early antiviral IFN-I responses and influence the accrual of virus-specific NK or CD8(+) T cells in a virus-dependent manner.

Figure 1. Generation of BDCA2-DTR Tg Mice and Selective Depletion of pDCs

(A) The construct for BDCA2-DTR Tg mice includes a 5 kb fragment upstream of the ATG of the BDCA-2 gene, a cDNA fragment encoding DTR, and the human growth hormone (hGH) gene polyadenylation signal. (B and C) DT administration specifically depletes pDCs in BDCA2-DTR Tg mice. Cell subsets in spleen (B) and blood (C) were analyzed by flow cytometry 24 hr after DT injection. Data shown are representative of at least three experiments. Classical DCs (cDC), macrophages (Mac), resident (R), inflammatory (I), monocytes (Mono), and granulocytes (PMN).

Figure 2. pDC-Mediated Inhibition of MCMV Replication Is Dependent on Viral Inoculum

(A and B) PBS- or DT-treated mice were infected i.p. with different doses of MCMV and viral titers in spleen (A) and liver (B) were enumerated on day 3 p.i. by plaque assay. (C) PBS- or DT-treated mice were infected i.p. with MCMV or Δm157 MCMV and salivary gland (SG) viral titers were calculated on day 8 p.i. p value, unpaired, two-tailed Student's t test. Data shown are from two experiments.

Figure 3. pDC Impact on Nonspecific and Specific NK Cell Activation during MCMV Infection

Mice were infected i.p. with MCMV (5 × 10⁴ pfu). (A) Frequencies of NK cells (NK1.1⁺CD3⁻) in spleens. (B) Expression of CD69 on splenic NK cells. (C) Cytotoxic capacity of splenic NK cells from control and pDC-depleted mice with RMA-S target cells in standard 4 hr ⁵¹Cr release assays. (D) Frequencies of IFN-γ⁺ NK cells in spleens of MCMV-infected mice. (E) Frequencies of Ly49H⁺ and IFN-γ⁺-producing NK cells on day 3 p.i. Data are representative of six to eight mice from two experiments. (F) Total numbers of NK1.1⁺ and Ly49H⁺NK1.1⁺ cells during MCMV infection. (B and D) p value, unpaired, two-tailed Student's t test. (C and F) Asterisks denote p values ≤ 0.03 as measured by unpaired, two-tailed Student's t test. (A–D, F) Data are from two experiments (mean ± SEM, n = 5–7).

Figure 4. Impact of pDCs on Cytokine Production, DC Activation, and Early Anti-MCMV CD8⁺T Cell Responses

(A, B, D–G) PBS- and DT-treated mice were infected i.p. with 5 × 10⁴ pfu of MCMV and serum samples were analyzed for IFN-α (A), IFN-γ (B), and IL-12p70 (D). (C) PBS- and DT-treated mice were infected i.p. with different doses of WT MCMV or Δm157 MCMV and serum IFN-γ concentrations were quantified 48 hr p.i. (E) Frequencies of IL-12⁺CD11c^hi cells were determined 48 hr p.i. by intracellular staining. (F) Expression based on mean fluorescence intensity (MFI) of costimulatory (CD86, CD40, CD80) and MHC class II molecules on CD11c^hi DCs. (G) Frequencies and absolute numbers of Ag-specific CD8⁺ T cells on day 6 p.i. p value, unpaired, two-tailed Student's t test. Data are from two (A, B, D–G) or three (C) experiments (mean ± SEM, n = 5–25).

Figure 5. pDCs Augment Ag-Specific CD8⁺T Cell Responses during VSV-OVA Infection

PBS- or DT-treated mice were infected i.v. with 5 × 10⁶ pfu (A, C–F) or 5 × 10⁵ pfu (B) of VSV-OVA. (A) IFN-α concentrations in serum were determined at 6, 12, or 24 hr p.i. (B) Viral titers in spleens were measured at 6 hr p.i. (C–F) Spleens from VSV-OVA-infected mice were analyzed on day 7 p.i. (C) Spleen cellularity. (D) Spleen cells from infected mice were stained with H-2K^b OVA_257-264 peptide tetramers and anti-CD8. Frequencies and totalnumbers ofAg-specific CD8⁺ T cells were determined by flow cytometry. (E) Frequencies and numbers of CD8⁺ T cells producing IFN-γ after restimulation with SIINFEKL were determined by flow cytometry. (A–E) p value, unpaired, two-tailed Student's t test. Data are from two to five experiments (mean ± SEM, n = 6–19). (F) Antigen-specific cytotoxicity was assessed in standard 4 hr ⁵¹Cr release assays. Asterisks denote pvalues ≤0.03 as measured by unpaired, two-tailed Student's t test. Data are from two experiments (mean ± SEM, n = 6–7).

Figure 6. pDCs Enhance Accumulation of Ag-Specific CD8⁺T Cells during VSV-OVA Infection

Purified CD8⁺ T cells from OT-I TCR Tg mice were CFSE labeled and adoptively transferred into BDCA2-DTR Tg mice. Mice were injected the following day with PBS or DT, then infected i.v. with VSV-OVA (5 × 10⁵ pfu) 24 hr later. Splenocytes isolated 66 hr p.i. were stained with anti-CD8 and -Vα2 then analyzed by flow cytometry. Data are from two experiments (mean ± SEM, n = 8). (A) Dot plots show the frequencies of CFSE⁺ cells among CD8⁺Vα2⁺ T cells. Histograms show the number of divisions based on CFSE dilution. (B) Frequencies and absolute numbers of CFSE⁺CD8⁺Vα2⁺ T cells. p value, unpaired, two-tailed Student's t test.

Figure 7. Recruitment and Survival of Ag-Specific CD8⁺T Cells during VSV-OVA Infection

(A) Serum concentrations of CCL4 in VSV-OVA-infected mice 24 hr p.i. Data are from three experiments. (B) Purified CD8⁺ T cells from OT-I TCR Tg mice were CFSE labeled and adoptively transferred into BDCA2-DTR Tg mice. Mice were depleted and infected as described in Figure 6. Splenocytes isolated at6or22 hr p.i. were stained with anti-Vα2then analyzed by flow cytometry. Dot plots show the frequencies of CFSE⁺ cells among Vα2⁺ cells. Data are representative of three to eight mice per group. (C) Mice were injected with 2 × 10⁶ CFSE-labeled CD8⁺ T cells from OT-I mice then infected in the footpad with VSV or VSV-OVA (1 × 10⁶ pfu) 24 hr later. Controlateral (CLN) and draining (DLN) lymph nodes were stained with anti-Vα2 and analyzed by flow cytometry at 9 or 25 hr p.i. Data are representative of three mice per group. (D) Mice were injected with CFSE- or eFluor 670-labeled OT-I cells, then depleted or not and infected as described in Figure 6. Splenocytes were stained with anti-CD8, anti-Vα2, and Annexin V or CaspACE FITC-VAD-FMK 45 or 66 hr p.i. Bar graphs show the frequencies of OT-I cells among CD8⁺Va2⁺ cells (top) and frequencies of apoptotic OT-I cells (bottom). Data are from two experiments (mean ± SEM, n = 4–8). p value, unpaired, two-tailed Student's t test.