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Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide

Abstract

Plasmacytoid dendritic cells (pDCs) sense viral and microbial DNA through endosomal Toll-like receptors to produce type 1 interferons. pDCs do not normally respond to self-DNA, but this restriction seems to break down in human autoimmune disease by an as yet poorly understood mechanism. Here we identify the antimicrobial peptide LL37 (also known as CAMP) as the key factor that mediates pDC activation in psoriasis, a common autoimmune disease of the skin. LL37 converts inert self-DNA into a potent trigger of interferon production by binding the DNA to form aggregated and condensed structures that are delivered to and retained within early endocytic compartments in pDCs to trigger Toll-like receptor 9. Thus, our data uncover a fundamental role of an endogenous antimicrobial peptide in breaking innate tolerance to self-DNA and suggest that this pathway may drive autoimmunity in psoriasis.

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Figure 1: LL37 is the key trigger of pDC activation in psoriatic skin.
Figure 2: LL37 converts self-DNA into a potent trigger of pDCs by forming aggregated and condensed structures.
Figure 3: Self-DNA coupled with LL37 is translocated into pDCs and activates them through TLR9.
Figure 4: LL37 retains DNA in early endocytic compartments of pDCs.

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Acknowledgements

We thank G. Lizee for critical reading of the manuscript; E. Wieder and K. Ramirez from the Flow Cytometry Core Facility for performing cell sorting; J. Wygant from the Monoclonal Antibodies Core Facility for generating the anti-LL37 monoclonal antibody; J. Bartels for ESI-MS analyses; and G. Reyes for technical assistance. This work was funded by a grant from the M. D. Anderson Cancer Foundation to M.G. Part of this work was supported by grants from the ‘Deutsche Forschungsgemeinschaft’ to J.-M.S. and to B.H.

Author Contributions R.L. performed and analysed most of the experiments in this study, and participated in their design. J.G. performed and analysed size-exclusion HPLC and helped in the atomic force microscopy experiments. V.F. and B.S. performed and analysed the experiments with transfected cell lines. B.C. and I.M. helped in establishing and analysing imaging experiments on endosomal trafficking. Yi-Hong Wang performed immunohistochemistry. B.H. collected and characterized clinical samples and participated in the expression analyses. W.C. generated the IRF7 construct. Yui-Hsi Wang helped in performing RT–PCR experiments. F.O.N. participated along with J.-M.S. and M.G. in the design of experiments with skin extracts. T.Z. helped in performing and evaluating imaging experiments using living cells. J.-M.S. designed, performed and evaluated the separation and biochemical analysis of skin extracts. Y.-J.L. provided critical suggestions and discussions throughout the study. M.G. conceived and supervised this study, was involved in the design and evaluation of all experiments, and wrote the manuscript with comments from co-authors.

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Correspondence to Michel Gilliet.

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Supplementary information

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This file contains Supplementary Figures S1-S7 and Legends. Figure S1 shows the identification of LL-37 in IFN-inducing HPLC fraction 26. Figure S2 shows the ability of genomic DNA of human and bacterial origin to induce IFN-α when coupled with LL-37. Figure S3 shows that the binding of LL-37 to DNA and the resulting structural changes in the DNA are reversible. Figure S4 shows internalization of LL-37 in the absence of DNA. Figure S5 shows that the ability of LL-37 to enhance DNA-mediated IFN-α requires the complex formation with the DNA. Figure S6 shows the preferential retention of LL-37-DNA in early endocytic compartments. Figure S7 shows the capacity of LL-37 to restore IFN-α induction by disrupted DNA aggregates. (PDF 1996 kb)

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Lande, R., Gregorio, J., Facchinetti, V. et al. Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide. Nature 449, 564–569 (2007). https://doi.org/10.1038/nature06116

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