CD169+ macrophages at the crossroads of antigen presentation

CD169(+) macrophages have fascinated immunologists because of their unique distribution in secondary lymphoid organs, redistribution upon immune activation and, lately, because of their contribution to antigen handling. Their association with B cell follicles prompted early studies on their involvement in B cell activation, and recent work has unveiled an unexpected role in facilitating activation of other lymphocyte subsets, such as invariant natural killer T (iNKT) cells. New data also argue that CD169(+) macrophages activate CD8 T cells in response to dead cell-associated antigens in lymph nodes and by transferring antigen to dendritic cells (DCs) in the spleen. Understanding the role of CD169(+) macrophages in the activation of acquired immunity could benefit the design of vaccination strategies, for example those aimed at eliciting cytotoxic T cells.