Duration, combination and timing: the signal integration model of dendritic cell activation.

The activation of resting dendritic cells (DCs) is a crucial step in the initiation of adaptive immunity because it links peripheral events initiated by the encounter with pathogens to the activation and expansion of antigen-specific T lymphocytes in secondary lymphoid organs. It is well recognized that a wide variety of microbial products and endogenous signals can trigger DC activation, and that different DC subsets are specialized in inducing different classes of immune responses. In this review, we will focus on how different aspects of DC maturation are regulated not only by the nature of the DC maturation stimuli, but also by their duration, combination and timing, and provide an overview of how different modes of DC activation can affect T cell responses.