These derivatives of peripheral blood monocytes are members of the mononuclear phagocyte system of cells.
Macrophages secrete a variety of cytokines, including interleukin-1 (IL-1), as well as other products, such as acid hydrolases, neutral proteases, and prostaglandins. In addition, they process and present antigen (along with human leukocyte antigen [HLA] class II antigens) to CD4+ T cells.
Macrophages also participate in delayed hypersensitivity reactions. They may be capable of directly killing tumor cells.
Dendritic cells of lymphoid tissue are characterized by dendritic cytoplasmic processes.
Dendritic cells express large quantities of cell-surface HLA class II antigens.
In contrast to macrophages, dendritic cells are poorly phagocytic; however, like macrophages, dendritic cells are antigen-presenting cells.
Langerhans cells of the skin
Ultrastructural characteristics include the presence of Birbeck granules, tennis racket–shaped cytoplasmic structures.
Like dendritic cells of lymphoid tissue, Langerhans cells of the skin express HLA class II antigens and are antigen-presenting cells.