Instead, the differential gene expression in the gingival tissues should more appropriately be attributed to the aggregate effect of the mixed microbial burden, and the specific investigated Vorinostat bacteria may simply serve as a surrogate for this mixed microbial burden to which they contribute. It must be further recognized that the gingival tissue transcriptomes are also influenced by a plethora of additional factors beyond those of bacterial origin, including biologically active host-derived molecules and tissue degradation byproducts, that could not be accounted for in our study. In view of the above, and because the transcriptomic profiles analyzed originate

from a mixed cell population comprising gingival epithelial cells, connective tissue fibroblasts and infiltrating cells, our data are not directly comparable with observations PKA activator from the aforementioned in vitro studies of mono-infections of oral epithelial cell lines. Nevertheless, our data corroborate

and extent data from these experimental settings. For example, ontology analysis of epithelial cell pathways differentially regulated after infection with F. nucleatum [14] identified MAPK signaling and regulation of actin cytoskeleton among the impacted pathways. Likewise, in line with observations by Handfield et al. [11], apoptotic mitochondrial changes, the second highest differentially

Protein kinase N1 regulated ontology group according to levels of A. actinomycetemcomitans was ranked 96th according to subgingival levels of P. gingivalis. Indeed, A. actinomycetemcomitans is known to exert strong pro-apoptotic effects on various cell types encountered in inflamed gingival tissues, such as gingival epithelial cells [37] or invading mononuclear cells [38], attributed in part to its potent cytolethal distending toxin [39]. On the other hand, P. gingivalis was shown to inhibit apoptosis in primary gingival epithelial cells by ATP scavenging through its ATP-consuming nucleoside diphosphate kinase [40]. In contrast, other in vitro studies involving oral epithelial cells (for review see [41]) reported apoptotic cell death induced by P. gingivalis at very high (up to 1:50,000) multiplicities of infection [42], which arguably exceeds the in vivo burden in the periodontal pocket. Thus, our data indicate presence of pro-apoptotic alterations in the gingival tissues in A. actinomycetemcomitans-associated periodontitis, while the effects of P. gingivalis appear to be primarily mediated by other pathways. Interestingly, our data corroborate a recent study that explored the hyper-responsiveness of peripheral blood find more neutrophils in periodontitis and demonstrated a significantly increased expression of several interferon-stimulated genes [43].