Dendritic cells in contact sensitivity.

Bone-marrow-derived DC, passing through the skin or residing there as LC, acquire antigen following epicutaneous exposure to contact sensitizer. They move as veiled cells in the afferent lymphatics and migrate to draining lymph nodes, where they become interdigitating cells of the paracortex. Here they initiate T-cell responses; the cytotoxic T cells and antibody formation which develop may be able to target on DC as well as other antigen-bearing cells, so producing feed-back mechanisms to switch off immune responses. Additional features include a systemic effect which leads to movement of DC without antigen into lymph nodes. What are the signals leading to this movement and what is its significance? There is evidence for synergy between directly haptenated DC and DC not directly acquiring antigen. How does this occur and how important is this effect in ensuring the potency of DC in presenting contact sensitizer to T cells? What is the importance of antigen processing by LC? Finally, dendriform cells which may be of T-cell origin are also present in the skin. What is their role in modulating the development of contact sensitivity?