Innate cellular responses to the periodontal biofilm.

This chapter addresses the host responses to the microbial biofilm that constitutes the subgingival dental plaque. The host response to infection draws upon the innate, inflammatory and adaptive immune systems, whose role is to provide the appropriate response to the offending microorganisms. In some cases, this will be little or no response when encountering 'commensals', and in other cases a gradated response depending very much on the host's own determination of the pathogenic nature of the microbial insult: and herein lies the root of variation in host responses that govern individual susceptibility. In some individuals and with some bacteria this will be an innate-only response, others will need to invoke the inflammatory response, and yet others will require the adaptive immune response - be it cellular, humoral or both - to reduce or remove the challenge from the microbes. Of course these responses would be somewhat easier to predict with a single pathogen challenge, and become infinitely more complex as the biofilm increases in complexity. Oral infections, in particular gingival inflammation, originate from not just one but many microorganisms. This polymicrobial infection may result in chronic inflammation, which may lead to tissue destruction, as evident in chronic periodontitis. Although many organisms are present in the subgingival biofilm, interestingly, the putative pathogens associated with gingivitis and periodontitis may comprise very small fractions of the total biomass. An understanding of the interaction of structural and defensive host cells with the biofilm is pivotal to understanding periodontal disease etiology and to developing tailored therapeutics. Thus, this chapter addresses the main structural cells, i.e. epithelial cells, exposed to the biofilm.