In addition to its various populations of lymphocytes, lymph nodes are composed of other cell types, including cells derived from the monocytic lineage, and cells that comprise the lymph node capsule and trabeculae, blood vessels and sinuses.

In this section, we focus on the cells derived from the monocytic lineage. These cells originate in the bone marrow from myelomonocytic progenitors and differentiate subsequently into various cell types, some circulating in the lymph and blood and others that migrate to various tissues. Tissue-based cells of monocytic lineage are generally referred to as the mononuclear phagocyte system and have been classified into various categories according to their morphology and function. Some of these cells become phagocytic macrophages/histiocytes, with the important role of removing and digesting particulate antigens. Others become antigen-presenting cells, with the main function of facilitating contact between foreign antigenic substances and the antigen-sensitive lymphoid cells. There are two major types of antigen-presenting cells in the lymph node, follicular dendritic cells (which may not be of monocytic lineage as discussed later), and interdigitating dendritic cells, located in the lymphoid follicles and paracortical regions, respectively. These cells are also referred to as accessory cells because of their important role in the B- and T-cell immune response, respectively.