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TH17 cells promote microbial killing and innate immune sensing of DNA via interleukin 26

Nature Immunology volume 16, pages 970–979 (2015)Cite this article

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Abstract

Interleukin 17–producing helper T cells (TH17 cells) have a major role in protection against infections and in mediating autoimmune diseases, yet the mechanisms involved are incompletely understood. We found that interleukin 26 (IL-26), a human TH17 cell–derived cytokine, is a cationic amphipathic protein that kills extracellular bacteria via membrane-pore formation. Furthermore, TH17 cell–derived IL-26 formed complexes with bacterial DNA and self-DNA released by dying bacteria and host cells. The resulting IL-26–DNA complexes triggered the production of type I interferon by plasmacytoid dendritic cells via activation of Toll-like receptor 9, but independently of the IL-26 receptor. These findings provide insights into the potent antimicrobial and proinflammatory function of TH17 cells by showing that IL-26 is a natural human antimicrobial that promotes immune sensing of bacterial and host cell death.

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Figure 1: IL-26 is a cationic amphipathic protein that forms oligomers.
Figure 2: IL-26 has direct bactericidal properties.
Figure 3: TH17 cells exert direct antimicrobial activity via the production of IL-26.
Figure 4: IL-26 promotes bacterial killing and concomitant sensing of DNA released by pDCs.
Figure 5: IL-26 promotes pDC sensing of human DNA released in the context of cell death.
Figure 6: IL-26–DNA complexes are endocytosed via heparan-sulfate proteoglycans and activate TLR9 in pDCs.
Figure 7: TH17 cells activate pDCs via IL-26 production.

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Acknowledgements

We thank K. Dunner for scanning electron microscopy at the HREM Facility, MD Anderson Cancer Center. We thank L. Bover and the Monoclonal Antibody Core Facility staff at the MD Anderson Cancer Center for assistance in generating monoclonal antibodies to IL-26. We thank the Berkeley Laboratory Advanced Light Source and the SIBYLS beamline staff at 12.3.1 for assistance with the collection of small-angle X-ray scattering data, and we thank K. Dyer for the mail-in service provided by SIBYLS. This work was funded by the Swiss National Science Foundation (grant 144072), the National Cancer Institute (PO1 grant CA128913) and the DANA Foundation (all to M.G.). S.M. was partly supported by the German Research Foundation and the research commission of the Medical Faculty of the University of Düsseldorf. Research by S.T.A. was supported by the King Abdullah University of Science and Technology (KAUST). T.R. is supported by the Swiss National Science Foundation (grant 149511).

Author information

Author notes

  1. Stephan Meller and Jeremy Di Domizio: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Immunology, University of Texas MD Anderson Cancer Center, Houston, Texas, USA

    Stephan Meller, Kui S Voo, Georgios Chamilos, Dipyaman Ganguly, Josh Gregorio & Michel Gilliet

  2. Department of Dermatology, Heinrich-Heine-University Medical Faculty, Düsseldorf, Germany.,

    Stephan Meller, Heike C Friedrich & Bernhard Homey

  3. Department of Dermatology, University Hospital CHUV, Lausanne, Switzerland

    Jeremy Di Domizio, Curdin Conrad & Michel Gilliet

  4. Department of Infectious Diseases, University of Texas MD Anderson Cancer Center, Houston, Texas, USA

    Georgios Chamilos & Dimitrios P Kontoyiannis

  5. Department of Infectious Diseases, University Hospital CHUV, Lausanne, Switzerland

    Didier Le Roy & Thierry Roger

  6. School of Molecular and Cell Biology, University of Leeds, Leeds, UK

    John E Ladbury

  7. Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas, USA

    Stanley Watowich

  8. Division of Dermatology, UCLA David Geffen School of Medicine, Los Angeles, California, USA

    Robert L Modlin

  9. Department of Respiratory, Inflammation and Autoimmunity, MedImmune, Gaithersburg, Maryland, USA

    Yong-Jun Liu

  10. Division of Biological and Environmental Sciences & Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia

    Stefan T Arold

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Contributions

S.M. and J.D.D. performed and analyzed most of the experiments and participated in their design. G.C. and J.G. helped establish, perform and analyze antimicrobial assays. D.G. performed TLR9 reporter assays and participated in the imaging studies. C.C. and K.S.V. helped establish the T cell culture experiments. H.C.F. performed ELISA analysis of the skin biopsies. J.E.L. and S.T.A. designed and performed the protein-modeling and small-angle X-ray scattering experiments. D.L.R. and T.R. provided virulent strains of bacteria and helped with the in vivo infectious model. B.H., D.P.K., Y.-J.L. and R.L.M. provided suggestions and discussions throughout the study. S.W. provided initial modeling data for IL-26. M.G. conceived and supervised the study, was involved in the design and evaluation of all experiments, and wrote the manuscript along with S.M. and J.D.D., with comments from other co-authors.

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Correspondence to Michel Gilliet.

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Integrated supplementary information

Supplementary Figure 1 Structural characterization of IL-26.

(a) Amino acid sequence of IL-26. Amino acids within the 6 predicted α-helical regions are labeled in red. Positively charged amino acids clustering on one side of the helix bundle are indicated in bold. Hydrophobic residues exposed on the other side of the bundle are underlined. (b) SAXS allows for study of the 3D structure of proteins in solution. Although this method does not reveal atomic details, its resolution is sufficient to determine the multimeric state and shape of a protein. SAXS analysis yields a scattering pattern (black dots). From this pattern, the radius of gyration Rg of the particle in solution can be derived in two model-independent ways: (i) from the Guinier analysis (Rg = 5.68 ± 0.1 nm), and (ii) through the indirect transform algorithm implemented in the program GNOM (5.59 ± 0.1 nm). The algorithm used in GNOM also provides the maximum diameter Dm of the solute particle (here 18.8 ± 0.2 nm). These experimentally determined Rg and Dm values are substantially larger than those calculated from a monomeric IL-26 structural model (Rg = 1.5 nm; Dm = 5.5 nm), or from dimeric IL-26 models (based on IL-22: Rg = 1.8 nm, Dm = 5.9 nm; based on IL-10: Rg = 2.3 nm, Dm = 7.5 nm), indicating that IL-26 forms multimers in our experimental conditions. (c) SAXS data can be used to determine a model-independent ab initio shape of the solute particle. For our data, this ab initio shape resembled four linearly connected spheres (gray beads obtained by the program DAMMIF). Each sphere has the dimensions of one IL-26 monomer. As illustration, one IL-26 molecule (secondary structure representation, color-ramped from blue: N terminus to red: C terminus) was placed by hand in the ab initio SAXS shape. Based on these results, we used the program SASREF to position four IL-26 monomers as a tetramer that best fits the experimental SAXS pattern. The calculated SAXS pattern (red line in b, produced with CRYSOL) of the resulting tetramer fitted the experimental data (black dots, b) with χ = 0.99. (For a good model, χ values should be close to 1. Values much greater than 1 indicate a poor fit of model to data, and χ values much smaller than 1 indicate over-fitting of the data.) SAXS yields the average size of all solute particles. Hence our analysis does not rule out the presence of minor populations of other multimers (3-mers and 5-mers, for example), which are expected to co-exist in a concentration-dependent equilibrium. Repeat runs of SASREF or DAMMIF (both of which use a Monte Carlo algorithm and simulated annealing, and hence can produce different models for each run) produce linear structures with similar, but not identical, curvature, each of which achieves a comparable χ fit. This observation suggests that IL-26 molecules do not form a rigid rod, and retain some flexibility between protomers. (d) Four cysteines are well placed to form disulfide bonds that stabilize the compact helix bundle. The atomic model of IL-26 (colored as in c) was obtained by homology modeling.

Supplementary Figure 2 Antimicrobial activity of rhIL-26.

(a) Growth of the virulent strains E. coli J5 O111:B4, E. coli O111:K58:H2, E. coli O18:K1:H7 and P. aeruginosa PA14 in culture with increasing concentrations of rhIL-26. (b) Flow cytometry analysis of K. pneumoniae O1:K2 (top) and P. aeruginosa PA14 (bottom) treated with increasing concentrations of rhIL-26 for 1 h and stained with SYTO 13 Green (permeant DNA dye) and SYTOX Orange (impermeant DNA dye). (c) Fluorescence microscopy imaging of K. pneumoniae O1:K2 in culture medium or treated for 1 h with 10 µM IL-26, and stained with SYTO 13 Green (permeant DNA dye) and SYTOX Orange (impermeant DNA dye). Left images show an overview of the bacteria; middle and right images show bacteria at higher magnification. (d) Growth of S. aureus ATCC 6538, E. coli O1:K1:H7 and P. aeruginosa ATCC 27853 in culture with increasing concentrations of rhIL-26 or LL-37. (e) Gorwth of E. coli O111:K58:H2, K. pneumoniae O1:K2 and P. aeruginosa PA14 in culture with 10 µM of IL-26, LL-37 or hBD3. a–e, Data are representative of three independent experiments. e, Error bars represent the s.d. of triplicates.

Supplementary Figure 3 IL-26 is mainly expressed by primary CD4+ TH17 cells and TH17 cell clones.

(a) Microarray gene-expression profile in isolated unstimulated or activated peripheral blood immune cell subsets. TH1, TH2 and TH17 cells were differentiated from naive T cells as described in the Online Methods. The results of the gene-expression profile of IL-26 are shown as the relative hybridization intensity level. Error bars represent the s.d. of duplicates. (b) Real-time PCR analysis of IL17A and IL26 mRNA expression in re-stimulated TH17 clones 1G3, 7H1 and 72G6, transfected with siRNA targeting IL-26 (siIL-26) or a control siRNA (siCtl). The feeder cell line LCL was used as a control (-). Error bars are the s.d. of triplicate wells. Data are representative of two independent experiments.

Supplementary Figure 4 Antimicrobial activity and interferon-inducing capacity of recombinant and natural TH17 cell–derived IL-26.

(a–c) Growth of P. aeruginosa treated with (a) increasing concentrations of rhIL-26, (b) supernatants of TH17 cell clones 1G3, 7H1, 72G6 or (c) supernatants of TH17 cell clones transfected with siRNA targeting IL-26 (siIL-26) or control siRNA (siCtl). Data are representative of two independent experiments. Data are means of duplicate wells. (d) IFN-α produced by pDCs stimulated overnight with exogenous human DNA in the presence of increasing concentrations of rhIL-26, IL-26–containing TH17 cell supernatants, or IL-26–containing TH17 cell supernatants treated with neutralizing anti–IL-26. Error bars represent the standard deviation of duplicate wells. Data are representative of two independent experiments.

Supplementary Figure 5 IL-26 forms complexes with bacterial DNA that activate pDCs to produce type I interferon.

(a) Gel shift assay of bactDNA mixed with increasing concentrations of rhIL-26 (left). Mixing with rhIL-17 or IL-22 was used as a control. (b) Fluorescence microscopy imaging of Alexa Fluor 488–labeled bactDNA mixed with rhIL-17, rhIL-22 or rhIL-26. (a,b) Data are representative of two independent experiments. (c) IFN-α produced by pDCs stimulated with increasing concentrations of IL-26 either alone or in complex with bactDNA. Data are representative of three independent experiments. Error bars represent the s.d. of duplicate wells. (d,e) IFN-α produced by pDCs stimulated overnight with (d) increasing concentrations of E. coli lysate (titrated according to DNA content) in the presence or not of IL-26, (e) E. coli lysate alone or in the presence of IL-26, with or without DNase pretreatment. d,e, Data are representative of three independent experiments. Error bars represent the s.d. of triplicate wells. Data in e were statistically analyzed via unpaired two-tailed Student’s t-test; *P < 0.01.

Supplementary Figure 6 Antimicrobial and cytotoxic activities of rhIL-26 and LL-37.

Viable bacteria and human neutrophils, monocytes, macrophages, pDCs and HEK cells following overnight culture in the presence of increasing concentrations of rhIL-26 (a) or LL-37 (b). MIC50 for bacteria and EC50 for human cells were calculated using nonlinear regression fit curves. Data are representative of two independent experiments. Error bars represent the s.d. of duplicate wells.

Supplementary Figure 7 IL-26–human DNA complex formation can be inhibited by anionic polymers and anti–IL-26.

(a,b) Fluorimetric quantification of DNA staining by picogreen dye upon mixing of human DNA with IL-26 in the presence of (a) increasing concentrations of the anionic polymer heparin or (b) neutralizing anti–IL-26 or anti–IL-17. (c) IFN-α produced by pDCs stimulated overnight with IL-26–human DNA complexes in the presence of neutralizing anti–IL-26 or isotype control antibodies (ctl IgG). Error bars represent the s.d. of triplicate wells. Data are representative of three independent experiments. Statistical analysis was done using unpaired two-tailed Student’s t-test; *P < 0.001.

Supplementary Figure 8 pDC activation by L-26–human DNA is not dependent on the IL-26 receptor and cytosolic DNA sensing.

(a) IFN-α produced by pDCs stimulated overnight with bactDNA or human DNA alone, with IL-26–bactDNA or IL-26–human DNA complexes, or with the STING ligand cGAMP in the presence of 100 ng/ml chloroquine. (b) IFN-α produced by pDCs stimulated overnight with human DNA alone or with IL-26–human DNA complexes in the presence of increasing concentrations of blocking antibodies to IL-10R2. Error bars represent the s.d. of triplicate wells. Data are representative of three independent experiments.

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Meller, S., Di Domizio, J., Voo, K. et al. TH17 cells promote microbial killing and innate immune sensing of DNA via interleukin 26. Nat Immunol 16, 970–979 (2015). https://doi.org/10.1038/ni.3211

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