Key Points

Ligature-induced periodontitis activates complement in a microbiota-dependent manner.

Complement C3 deficiency inhibits LIP-induced IL-6 and IL-23 and Th17 expansion.

Complement links the periodontal microbiota to Th17 expansion and bone loss.

Abstract

In both mice and humans, complement and Th17 cells have been implicated in periodontitis, an oral microbiota-driven inflammatory disease associated with systemic disorders. A recent clinical trial showed that a complement C3 inhibitor (AMY-101) causes sustainable resolution of periodontal inflammation, the main effector of tissue destruction in this oral disease. Although both complement and Th17 are required for periodontitis, it is uncertain how these immune components cooperate in disease development. In this study, we dissected the complement–Th17 relationship in the setting of ligature-induced periodontitis (LIP), a model that previously established that microbial dysbiosis drives Th17 cell expansion and periodontal bone loss. Complement was readily activated in the periodontal tissue of LIP-subjected mice but not when the mice were placed on broad-spectrum antibiotics. Microbiota-induced complement activation generated critical cytokines, IL-6 and IL-23, which are required for Th17 cell expansion. These cytokines as well as Th17 accumulation and IL-17 expression were significantly suppressed in LIP-subjected C3-deficient mice relative to wild-type controls. As IL-23 has been extensively studied in periodontitis, we focused on IL-6 and showed that LIP-induced IL-17 and bone loss required intact IL-6 receptor signaling in the periodontium. LIP-induced IL-6 was predominantly produced by gingival epithelial cells that upregulated C3a receptor upon LIP challenge. Experiments in human gingival epithelial cells showed that C3a upregulated IL-6 production in cooperation with microbial stimuli that upregulated C3a receptor expression in ERK1/2- and JNK-dependent manner. In conclusion, complement links the periodontal microbiota challenge to Th17 cell accumulation and thus integrates complement- and Th17-driven immunopathology in periodontitis.

Footnotes

This work was supported by Division of Microbiology and Infectious Diseases, National Institute of Allergy and Infectious Diseases Grant AI068730 (to J.D.L.) and by National Institute of Dental and Craniofacial Research Grants DE015254 and DE021685 (to G.H.).

The online version of this article contains supplemental material.

H.W. designed and performed research, analyzed data, and contributed to writing the manuscript; H.I. designed and performed experiments and analyzed data; T.K., D.C.M. and J.D.L. interpreted data and edited the manuscript; G.H. conceived and designed the study, supervised research, interpreted data, and wrote the manuscript.

Abbreviations used in this article:

ABCalveolar bone crestCEJcementoenamel junctionHIGKhuman immortalized gingival keratinocyteLIPligature-induced periodontitisMMPmatrix metalloproteinaseMOImultiplicity of infectionRANKLreceptor-activated NF-κB ligandVDNvancomycin-doripenem-neomycinWTwild-typeReceived May 9, 2022.Accepted July 27, 2022.Copyright © 2022 by The American Association of Immunologists, Inc.