Dendritic cells heterogeneity and its role in cancer immunity.

Dendritic cells are the most potent 'professional' antigen-presenting cells, with high ability of primary immune response initiation. Dendritic cells originate from bone marrow progenitors, which circulate in peripheral blood and subsequently give rise to immature dendritic cells, which reside in peripheral tissues. When dendritic cells encounter danger signals, they undergo differentiation and maturation; thereafter they migrate to lymphatic tissues, where they synapse with T-cells and initiate primary immune response. The immune response efficiency is determined by Th1/Th2 balance. Although dendritic cells represent a rare group of leukocytes, their functional and phenotypical heterogeneity confer a great challenge to immunologists. In this review, the myeloid and lymphoid development pathways of dendritic cells, are discussed. The heterogeneity of dendritic cells will be reviewed, based on their anatomical locations, phenotypes and functions. This section focuses on blood and lymphoid tissue dendritic cells. Subsequently, the roles of dendritic cells in the immunity of cancer and how cancer bypasses the dendritic cell-mediated immune responses, are discussed.