How has research into cytokine interactions and their role in driving immune responses impacted our understanding of periodontitis?

Objective: To review current knowledge on cytokine interactions and the cytokine-mediated links between innate and adaptive immunity that are relevant to the pathophysiology of periodontitis. Materials and Methods: A structured review of the literature was undertaken to identify relevant research publications using a Medline search from 1950 to September 2010. The focus of the search was on the functional role of cytokines, i.e. their actions and responses relevant to the pathogenesis of periodontal disease rather than more descriptive studies of their expression in tissues and body fluids. It was not possible to conduct a traditional systematic review with a focussed question due to the heterogeneity of published research. Results: There is enormous heterogeneity in the periodontal literature in terms of experimental approaches. We have the deepest understanding of the role of the proinflammatory cytokines [e.g. interleukin (IL)-1β, tumour necrosis factor-α, IL-6] with accumulating data on T-cell regulatory cytokines (e.g. IL-12, IL-18), chemokines and cytokines which mediate bone cell development and function (e.g. receptor activator of NFκB ligand, osteoprotegerin). It is clear that there are multiple, overlapping and complex functional links between cytokines with regulatory control exerted at a number of levels and involving numerous cell types (both immune cells and resident cells in the periodontium). Conclusion: Cytokines appear to interact functionally in networks in the periodontium and integrate aspects of innate and adaptive immunity. However, our understanding is far from complete, particularly how molecular and cellular pathways relate to disease pathogenesis. We should adopt consistent experimental approaches to gain better insight into the totality of cytokine networks and how they drive immune responses in the periodontium.