This threshold could be numerical or physiological, Apoptosis Compound Library cell line or a combination of both. It therefore takes a “team effort” to cause periodontitis in that the disease requires cooperative

interactions among bacteria with different roles. A recently formulated model that accommodates these concepts is called the polymicrobial synergy and dysbiosis (PSD) model [2]. This model holds that physiologically compatible organisms assemble into heterotypic communities, which exist in a controlled immunoinflammatory state. While they are pro-inflammatory and can produce toxic products such as proteases, overgrowth and overt pathogenicity are controlled by the host response. The microbial constituents of the communities can vary among individuals, among sites, and over time. Colonization by keystone pathogens such as P.

gingivalis elevates the virulence of the entire community following interactive communication with accessory pathogens. Initially, host immune surveillance is impaired and the dysbiotic community increases in number. Subsequently, the community proactively induces inflammation to sustain itself with derived nutrients, which will also shape a modified “inflammophilic” community. The action of pathobionts in the community, in addition to overt pathogens, eventually leads to destruction of periodontal tissues. The PSD model reconciles a number of features of periodontal Selleckchem SB431542 disease that were discordant with earlier concepts of pathogenicity. These include: the variable microbiota at disease sites, even within the same patient; the presence of pathogens

in the absence of disease; the episodic nature of the disease; and the failure of P. gingivalis to cause periodontitis in the absence of the commensal microbiota [13]. Bacteria on human mucosal surfaces tend to accumulate into complex multispecies communities, a process controlled by a sophisticated series of interbacterial signaling and host response interactions. Within these communities, bacteria have specialized roles, such as provision of an essential enzyme for progressive nutrient metabolism. Bacteria Verteporfin that influence the pathogenicity of the entire community are keystone pathogens, the best-documented example of which is P. gingivalis. While P. gingivalis can affect gene and protein expression in other community members, the major keystone-related influence of the organism is likely through interference with host immunity. This is accomplished by a multipronged approach that compromises immune function on a number of levels (Fig. 1 and 3). It is important to bear in mind, however, that periodontitis is an inflammatory disease, and thus the timing, location, and context of immune suppression by P. gingivalis will have major significance for the ultimate progression of disease.