The immune response of oral epithelial cells induced by single-species and complex naturally formed biofilms

In the oral cavity, the surfaces are constantly exposed to a complex variety of microorganisms organized in biofilms. As part of a sophisticated local immune response, gingival epithelial cells (GECs) express antimicrobial peptides, such as human beta-defensin-2 (hBD-2), ribonuclease 7 (RNAase-7), and psoriasin (PSO), and pro-inflammatory mediators, such as interleukin-8 (IL-8) and 5-lipoxygenase (5-LO). The aim of the present study was to test whether GECs show a differential immune response to single-species biofilms compared with multi-species biofilms.

GECs were cultured from biopsies derived from three different healthy donors (n = 3). To obtain naturally formed biofilm (NFB), polymer disks were attached to prostheses and carried intraorally for 12, 24, 36, and 48 h. In addition, single-species biofilms (SSB; Streptococcus mutans and Streptococcus mitis) were cultured on polymer disks in vitro (12, 24, 36, and 48 h). The messenger RNA (mRNA) expression of hBD-2, RNAase-7, PSO, IL-8, 5-LO, and glycerylaldehyde-3-phosphate dehydrogenase was analysed using semi-quantitative reverse transcription-polymerase chain reaction.

In GECs, the hBD-2 mRNA expression was significantly upregulated in response to S. mitis-biofilm stimulation compared with S. mutans-biofilm stimulation (P < 0.0001). In contrast, the RNAase-7 mRNA expression was significantly higher in GECs when responding to both S. mutans biofilms and naturally formed biofilms compared with S. mitis biofilms (P < 0.0001 and P < 0.001, respectively). The IL-8 and 5-LO mRNA was significantly upregulated in response to S. mutans biofilms (P < 0.0001 and P = 0.0002, respectively).

This in vitro study found biofilm-dependent expression of antimicrobial peptides and inflammatory mediators in GECs.