Bacterial-epithelial cell interactions in the periodontal diseases
Periodontal diseases result from a complex interaction between a biofilm containing commensal and periopathogenic bacteria and the host innate and acquired defense systems. The interaction of oral commensal and pathogenic bacteria and their effect on ' cell behaviour, particularly the synthesis of antibacterial and inflammatory molecules, has been the focus of this project. The messenger RNA (mRNA) and protein expression of human beta-defensin and pro-inflammatory cytokine mRNA in the gingiva of patients suffering from the periodontal diseases was also determined. Patients suffering periodontal diseases showed increased mRNA expression of human beta-defensins and cytokines compared to controls, however, there was no difference in human beta-defensin protein expression between diseased and control tissue samples. Further studies were then carried out to determine the effect of oral commensal and periopathogenic bacteria and their surface components on oral epithelial cells (OECs). An oral squamous carcinoma cell line was found to produce IL-8 protein and express mRNA for human beta-defensin 2 (hpD-2), both of which were induced by several oral bacterial cell surface components, including LPS. The stimulatory effect of LPS was subsequently found to involve the LPS receptor, CD 14. The presence of toll-like receptor mRNA was also demonstrated and results showed that their expression may be regulated by bacteria associated molecular patterns. Both live- and heat-killed oral bacterial pathogens, A. actinomycetemcomitans and P. gingivalis induced production of IL-8 protein and hpD-2 mRNA from OECs. Exposure to the oral commensals S. sanguis and S. gordonii resulted in a decrease in the production of IL-8 mRNA from OECs, whilst heat-killed S. sanguis upregulated hpD-2 mRNA. A highly invasive strain of A. actinomycetemcomitans was shown to adhere to OECs to a greater degree, and also led to a greater induction of hpD-2 mRNA and IL-8 protein compared to a non-invasive strain. Further, isogenic mutants of the oral commensal S. gordonii DL1 Challis, deficient in the production of antigen I/II-family proteins SspA and SspB and the fibrillar cell surface proteins CshA and CshB, showed reduced adhesion to OECs. All strains had comparable effects on IL-8 protein and hpD-2 mRNA expression in OECs. The results presented in this thesis demonstrate the expression profile of human beta- defensins and cytokines in healthy and diseased gingival tissue. hpD-2 has been shown to be upregulated in oral epithelial cells by a range of oral commensal and pathogenic bacteria and their products. It has also been shown that the invasive nature of oral bacteria may contribute to increased expression of hpD-2 messenger RNA in oral epithelial cells. The upregulation of hpD-2 mRNA by a wide variety of components, bacterial or otherwise in oral epithelial cells may have therapeutic potential, however further studies would need to be carried out to determine the correlation between mRNA and protein expression of hpD-2.