The complement system as a key modulator of the oral microbiome in health and disease

Abstract

In this review, we address the interplay between the complement system and host microbiomes in health and disease, focussing on oral bacteria known to contribute to homeostasis or to promote dysbiosis associated with dental caries and periodontal diseases. Host proteins modulating complement activities in the oral environment and expression profiles of complement proteins in oral tissues were described. In addition, we highlight a sub-set of bacterial proteins involved in complement evasion and/or dysregulation previously characterized in pathogenic species (or strains), but further conserved among prototypical commensal species of the oral microbiome. Potential roles of these proteins in host-microbiome homeostasis and in the emergence of commensal strain lineages with increased virulence were also addressed. Finally, we provide examples of how commensal bacteria might exploit the complement system in competitive or cooperative interactions within the complex microbial communities of oral biofilms. These issues highlight the need for studies investigating the effects of the complement system on bacterial behaviour and competitiveness during their complex interactions within oral and extra-oral host sites.

Keywords:

• Oral microbiome
• complement system
• dental biofilms
• dental caries
• streptococci

Author contributions

ROMG designed the review strategy. LAA performed the BLAST analysis. ROMG wrote the original draft. ROMG and MIK prepared the figures. ROMG, LAA, and MIK revised and edited the manuscript. All authors read and approved the final manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors were supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP: grants n^o. 2021/13074-9, 2021/06801-1, 2018/02054-4, 2015/12940-3, 2012/51832-3, 2012/50966-6, 2009/54182-7; fellowships n^o. 2017/19899-4, 2016/17216-4, 2015/07237-1, 2012/04222-5), by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001, and by the National Council for Scientific and Technologic Development (CNPq: grants n^o. 304480/2019-3).