Dendritic cell activation induced by various stimuli, e.g. exposure to microorganisms, their products, cytokines, and simple chemicals as well as adhesion to extracellular matrix.

Before the establishment of procedures to cultured dendritic cells (DCs) from peripheral blood or bone marrow progenitor cells using a combination of several cytokines, Langerhans cells (LCs) of the epidermis have been used as the best characterized dendritic cell population. The studies using LCs freshly isolated from the skin or DCs from the blood or spleen and cultured DCs from progenitors have elucidated that although DCs are a unique cell population characterized by their potent antigen presenting function, especially by their induction of primary antigen-specific T cell responses, they are immature and less potent in antigen presenting function immediately after isolated from the skin or from other non-lymphoid tissues. Therefore, DCs must be stimulated to augment their antigen presenting function and to initiate a naive T cell response. Recently, it becomes clear that a variety of signals, such as microorganisms, cytokines, adhesion to extracellular matrix, and simple chemicals like haptens, can induce this activation process in DCs, which is also called as DC maturation. In this paper, we discuss what kinds of stimuli effectively activate DCs.