Key Words

activation of the so-called mixed lymphocyte reaction used to characterize the major histocompatibility locus [2, 3]. DCs are now recognized as the most potent class of antigen-presenting cells that play central roles in the ini-tiation and control of the adaptive immune response [4, 5]. These cells ultimately help regulate the immune deci-sions that moderate the balance between tolerance and immunity [6, 7]. DCs are highly migratory cells that move from tissue to lymph nodes via afferent lymphatics where they then encounter naïve T cells ( fig. 1). At steady state, they reside in the peripheral organs as immature cells with a high phagocytic activity. This allows them to constantly sam-ple antigens from the extracellular space. Proteolytic en-zymes within the cell digest the captured antigens into fragments (peptides), which are then presented at the DC cell surface via major histocompatibility complex (MHC) class I and class II proteins. In the absence of inflamma-tion, DCs have high phagocytic activity, low T cell stimu-latory capacity, and are involved in the regulation of im-mune tolerance. Upon exposure to microbial products or inflammatory stimuli, DCs undergo functional matura-tion and licensing to become potent activators of T cell immunity. The induction of high levels of costimulatory molecules and the secretion of T cell-activating cytokines (IL-12) are factors that define the T cell stimulatory ca-pacity of DCs