Dendritic Cells

Abstract

Dendritic cells (DCs) represent a complex network of antigen-presenting cells that play a crucial role in the initiation of primary immunity, as well as maintaining the balance between immune tolerance and reactivity [1]. The modern field of DC biology was initiated in 1973 by Steinman and Cohn, who identified a subpopulation of murine splenocytes that had distinctive morphologic and phenotypic characteristics and powerfully stimulated T cell responses [2]. DCs have subsequently been described as the most potent antigen-presenting cells, which demonstrate the unique capacity to induce primary immune responses. Stimulation of naive T cells requires antigen presentation in the context of co-stimulatory and adhesion molecules, which serve as secondary signals needed for the activation of primary immunity. Antigen-presenting cells, such as B cells and macrophages, are effective in maintaining immune responses, but are incapable of initiating primary responses to novel antigens. In contrast, DC richly express MHC class I, II, co-stimulatory and adhesion molecules and are uniquely potent in initiating cellular immunity (Fig. 45-1) [3-6]. DCs also mediate humoral responses through the activation of helper T cells and direct effects on B cells [7]. DC activation of innate immunity has been demonstrated through their effects on NK cells and NKT cells [8, 9]. DCs have emerged as an area of intense interest in the fields of tumor immunotherapy and transplant biology.