Antimicrobial Effect of Human Gingival Keratinocytes and Gingival Stem Cells on Oral Bacteria

Objectives: A variety of human tissue cells including oral epithelial cells are known to produce antimicrobial peptides upon microbial challenge. In this study, we investigated the response of human gingival mesenchymal stem cells (GMSCs) in comparison with human immortalized gingival keratinocytes (HIGKs) to Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus gordonii. Understanding the effect of oral bacteria on antimicrobial peptide expression in different tissues is the first step of studying the mechanism of how different cell types defend themselves against pathogenic bacteria.
Methods: Both, GMSCs and HIGKs were exposed individually to Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus gordonii for 24 hours. Bacterial viability was determined by colony forming unit (CFU) counts. RT-PCR was used to quantify the expression of selected antimicrobial peptides, HBD2 and LL-37, in the cell lines used.
Results: CFU counts of F. nucleatum and S. gordonii exposed to the different cell lines were lower compared to controls. In contrast, CFU counts of P. gingivalis were higher in the presence of eukaryotic cells compared to cell-free controls. Both cell lines exhibited differential expression profiles in the presence of the different bacterial species compared to unchallenged controls.
Conclusions: CFU counts suggest that both GMSCs and HIGKs inhibit the growth of F. nucleatum and S. gordonii, while they enhance the growth of P. gingivalis. The expression patterns of HBD2 and LL-37 induced by the different bacterial species suggests differences in susceptibility to these antimicrobial peptides produced, consistent with previous reports for antimicrobial peptide susceptibility of some of the species tested.