Antibody neutralization of microbiota-derived circulating peptidoglycan dampens inflammation and ameliorates autoimmunity

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Abstract

The human microbiota provides tonic signals that calibrate the host immune response1,2, but their identity is unknown. Bacterial peptidoglycan (PGN) subunits are likely candidates since they are well-known immunity-enhancing adjuvants, released by most bacteria during growth, and have been found in the blood of healthy people3,4,5,6,7. We developed a monoclonal antibody (mAb), 2E7, that targets muramyl-l-alanyl-d-isoglutamine (MDP), a conserved and minimal immunostimulatory structure of PGN. Using 2E7-based assays, we detected PGN ubiquitously in human blood at a broad range of concentrations that is relatively stable in each individual. We also detected PGN in the serum of several warm-blooded animals. However, PGN is barely detectable in the serum of germ-free mice, indicating that its origin is the host microbiota. Neutralization of circulating PGN via intraperitoneal administration of 2E7 suppressed the development of autoimmune arthritis and experimental autoimmune encephalomyelitis in mice. Arthritic NOD2−/− mice lacking the MDP sensor did not respond to 2E7, indicating that 2E7 dampens inflammation by blocking nucleotide-binding oligomerization domain-containing protein 2 (NOD2)-mediated pathways. We propose that circulating PGN acts as a natural immune potentiator that tunes the host immune response; altering its level is a promising therapeutic strategy for immune-mediated diseases.

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Fig. 1: Characterization of 2E7 and development of icELISA for PGN quantification.
Fig. 2: PGN levels in the serum.
Fig. 3: Increasing the level of circulating PGN promotes CIA development.
Fig. 4: Therapeutic effect of 2E7 on CAIA.

Data availability

All data that support the findings of this study are either included in this published article and its Supplementary Information or available from the corresponding author upon request.

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Acknowledgements

We thank N.A.R. Gow, J. Heitman, and D. Ko for suggestions on the manuscript and helpful discussions. We thank N. Kaliaperumal and J. Connolly for their kind help with the Luminex and flow cytometry analyses, and W.E. Goldman for providing TCT. This work was supported by National Medical Research Council grant no. BMRC/BnB/0001b/2012 awarded to Y.W., L.C., and N.P.

Author information

Z.X.H. and Y.W. conceptualized the experiments. Z.X.H. and X.L.X. performed the experiments. X.L.X. and J.H.W. raised the monoclonal antibodies. H.S.W. performed the LC–MS analysis. Y.Q. isolated PGN subunits. W.C.C. conducted PGN assays in serum. S.X. and K-P.L analyzed adaptive immune response. L.C. and F.C. collected the blood samples from healthy volunteers. M.O., L.A.B.J., and M.N. collected the blood samples from donors of European ancestry. C.Y.L.N and K.P.L collected clinical samples. P.K. and S.P. raised the germ-free mice and provided serum samples. N.P. performed the statistical analyses. Y.W., L.C., and N.P. acquired the funding. Y.W. supervised the project. Y.W. and Z.X.H. wrote the manuscript.

Correspondence to Yue Wang.

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Supplementary Figures 1–9, Supplementary Tables 1 and 2, and Supplementary References.

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