Lymph node macrophages.

Lymph node (LN) macrophages have long been known for their efficient uptake of lymph-borne antigens. A convergence of studies on innate and adaptive immune responses has led to exciting recent advances in understanding their more specialized properties: presenting antigens to B cells, dendritic cells and T cells, producing trophic factors and cytokines, and, remarkably, being permissive for viral infection, a property critical for mounting anti-viral responses. LN macrophages have been traditionally divided into subsets based on their subcapsular sinus and medullary locations. Here, we classify LN macrophages into three subsets: subcapsular sinus macrophages, medullary sinus macrophages and medullary cord macrophages. We review the literature regarding the roles of these cells in innate and adaptive immune responses and requirements for their development. We also discuss challenges associated with their purification as well as the existence of additional heterogeneity among LN macrophages.