Fundamental mechanisms of host immune responses to infection.

Chronic inflammatory periodontal disease is caused by host immune responses to periodontal microorganisms. Although periodontal disease seems to progress locally in the oral cavity, the actual immune responses proceed at two sites, one being the local area peripheral to the periodontium, and the other being in secondary lymphoid tissues, such as lymph nodes and the spleen. To investigate the pathogenesis of periodontal diseases, it is essential to understand exactly how the immune system works against microbial infections. The past decade has produced remarkable advances in our understanding of host immune responses. This review highlights two of these developments: cross-talk between innate and adaptive immunity mediated by dendritic cells via toll-like receptors; and antigen-specific immune regulation by dendritic cells and T cells.