We investigated the differentiation and trafficking of inflammatory monocytes that phagocytosed subcutaneously injected fluorescent microspheres. As expected, most of the monocytes became microsphere+ macrophages, which remained in subcutaneous tissue. However, about 25% of latex+ cells migrated to the T cell area of draining lymph nodes, where they expressed dendritic cell (DC)-restricted markers and high levels of costimulatory molecules. Microsphere-transporting cells were distinct from resident skin DCs, and this transport was reduced by more than 85% in monocyte-deficient osteopetrotic mice. Thus, a substantial minority of inflammatory monocytes carry phagocytosed particles to lymph nodes and differentiate into DCs.

Differentiation of Phagocytic Monocytes into Lymph Node Dendritic Cells In Vivo