Potential immunological functions of salivary Hsp70 in mucosal and periodontal defense mechanisms

Molecular chaperones were considered to be intracellular, but there is increasing evidence demonstrating their cytoprotective and immune modulator properties outside the cell. The major extracellular chaperone (Hsp70) was also found in saliva, indicating a possible effect of Hsp70 on mucosal surfaces. Here we summarize the immune-modulatory role of the 70-kDa stress protein family, with special attention on the potential impact of salivary Hsp70 on oral defense mechanisms. There are three major facets of Hsp70-induced immune activation: 1) the appearance of Hsp70 on the surface of certain tumor cells or virally infected cells, leading to their phagocytosis and subsequent lysis; 2) the role of extracellular uncomplexed Hsp70 as a danger signal, leading to the secretion of proinflammatory cytokines from antigen-presenting cells and T lymphocytes and of nitric oxide from macrophages as well as to complement activation; 3) receptor-mediated uptake of peptide-loaded Hsp70 to antigen-presenting cells and cross-presentation of the Hsp70-peptide complex as an antigen to cytotoxic T cells and natural killer lymphocytes. The immune-activating effect of salivary Hsp70 may also be highly important in oral defense, especially in areas where molecular and cellular participants of the immune response appear on the surface of the oral cavity (i.e. several lesions of the mucosa and the periodontal tissues).