Oral commensals and pathogens enhance hBD-2 expression in HOKs

Abstract

Objectives: Human β-defensins (hBDs) are antimicrobial peptides expressed by epithelial cells and leukocytes that resist the microbial colonization. Notably, hBD-2 has both antibacterial activity and chemoattractant effects, and therefore plays a vital role in innate immune system. The present study investigated hBD-2 expression in a model of human oral keratinocytes (HOKs) in response to oral commensal and periodontopathogenic bacteria. Cell surface receptors involved in the bacteria-host interaction were examined. Methods: Representative oral commensal bacteria (Streptococcus mitis, Smi and Streptococcus sanguinis, Ss) and pathogenic bacteria (Porphyromonas gingivalis, Pg) were selected. The expression of hBD-2 in the interaction of HOKs with the species was assessed in a bacteria-HOKs co-culture model during a time course of 15 to 120 min, using both ELISA and qPCR. Toll-like receptors (TLR) 2 and 4 were analyzed using qPCR and antibody-mediated blocking assays.

Results: Multiplicity of infection (MOI) 10 was found to be appropriate for the co-culture model. Overall, Smi, Ss and Pg significantly upregulated the expression of hBD-2 in HOKs with reference to the control (p<0.05). As compared to the control Ss and Pg greatly stimulated hBD-2 expression at 30 (p<0.05), 60 (p<0.01) and 120 min (p<0.05). Whereas, the significant upregulation of hBD-2 was only observed at 60 and 120 min in HOKs stimulated by Smi. Blocking assays showed

that Smi- and Ss-stimulated expression of hBD-2 in HOKs was through both TLRs 2 and 4, while blockage of TLRs 2 and 4 did not significantly affect hBD-2 expression.

Conclusion: This study suggests that hBD-2 expression in HOKs may be significantly enhanced by the challenge of Smi, Ss and Pg. TLRs 2 and 4 are involved in the Smi- and Ss-stimulated expression of hBD-2 in HOKs. Supported by the Hong Kong RGC (HKU768411M and HKU767512M) and the Modern Dental Laboratory/HKU Endowment Fund to LJJ.