Immunologic characteristics of human gingival fibroblasts in response to oral bacteria

There is ample evidence that gingival fibroblasts (GFs) participate in the immune response to oral bacteria and serve as immune-regulatory cells. The objective of this study was to investigate the innate immune response of GFs to oral bacteria.

Human GFs were cocultured with relatively less-pathogenic (Leptotrichia wadei, Fusobacterium nucleatum and Campylobacter gracilis) and pathogenic red-complex bacteria. The expression of mRNA for antimicrobial peptides [AMPs; namely human beta defensins (HBDs)], chemokines with antimicrobial activity [chemokine C-X-C motif (CXCL)10, CXCL11 and chemokine C-C motif ligand 20 (CCL20)] and proinflammatory mediators [interleukin (IL)6 and IL8] and the levels of CXCL11, CCL20, IL-6 and IL-8 accumulated in supernatants were analyzed using real-time PCR and ELISA, respectively. The proteolytic activities of CXCL11, CCL20, IL-6 and IL-8 produced by six species of bacteria were also determined.

The relatively less-pathogenic bacteria strongly up-regulated the expression of antimicrobial chemokines and proinflammatory mediators, whereas the red-complex bacteria stimulated low levels, or often suppressed, expression of these factors. Regarding the regulation of AMPs, the inhibition of HBD3, HBD106 and HBD107 mRNAs by Porphyromonas gingivalis was noticeable; however, differences between the two bacterial groups were not conspicuous. Differential degradation of proteins by the six bacterial species was observed: P. gingivalis and Treponema denticola degraded proteins well, whereas the other species degraded proteins to a relatively lower degree.

The invasion of red-complex bacteria into gingival connective tissue can suppress the immune response of GFs and can be a source of persistent infection in connective tissue.