Impact of stromal cells on dendritic cells

Dendritic cells (DCs) are highly specialized antigen-presenting cells (APC) of hematopoietic origin. Acting as sentinels of the immune system, they collect and process antigenic material from the periphery that, due to their unique migratory ability, they can transport to secondary lymphoid organs for presentation to naive T cells. This interaction of DCs with T cells initiates a primary immune response or induces antigen-specific tolerance, depending on the type of DC and its activation state. Recent views suggested that tissue DCs are generated locally from a reservoir of immediate DC precursors rather than by a continuous flux of a DC pool from the bone marrow. Monocytes are well-known precursors for macrophages. However, because of their developmental plasticity, they can also differentiate into DCs. In humans, two monocyte subsets that vary in adhesion molecule and chemokine-receptor (CCR) expression as well as in migratory and differentiation properties can be distinguished: the classical CD14 + CD16 - monocytes that, based on the expression of CCR2, are rapidly recruited to sites of inflammation, and the non-classical CD14 low CD16 + monocytes that express the receptor for CX 3 CR1, but lack CCR2, and fulfill critical roles in replacing resident DCs or macrophages in the steady state. Their counterparts in mice are Gr-1high and Gr-1low monocytes, respectively. Despite the increasing rate of progress in monocyte biology during both inflammation and the steady state the mechanisms how monocytes are recruited into tissues and what determines their differentiation into migratory DCs or macrophages remains unclear. Of note, the influence of ancillary cells, such as fibroblasts and mast cells, on these processes has been utterly neglected. The objective of this project proposal is therefore to investigate how stromal fibroblasts and mast cells can promote monocyte trafficking into the connective tissue and cause monocytes to become DCs versus macrophages, and how they support their migration into the lymphatic vessels. The trafficking of blood DCs that is still poorly understood will be followed as well to provide insight into whether and how signals from fibroblasts and/or mast cells may alter their recruitment across endothelium. To mimic the physiological situation in the peripheral tissue, an integrated endothelial-matrix culture system with dual interface for cell entry and exit will be used. The aim is to gain a better understanding of the mechanisms involved in controlling the molecular and cellular events of DC differentiation and migration.