Oral mucosal immunity.

Oral keratinocytes and dendritic cells of the oral mucosa, through molecular pattern recognition receptors, distinguish between commensal and pathogenic microorganisms and mediate the generation of protective immunoinflammatory responses to potentially invading pathogens or mediate immune tolerance toward commensal microorganisms. Oral immune tolerance is the result either of lack of activation of T cells in response to immunogenic presentation of antigens or of suppression of activity of effector T cells by regulatory T cells. Secretory immunoglobulin A (sIgA) antibodies at oral mucosal sites contribute to oral immunity by limiting colonization of microorganisms and their invasion of the epithelium. Ig isotype class switching to IgA is either dependent on or independent of T helper cells and is facilitated by cytokines secreted by dendritic cells and monocytes.