Non-Primate Monocytes - CD14, CD16 - Ziegler-Heitbrock

Toward a functional characterization of blood monocytes.

Abstract

Monocytes are bone marrow-derived circulating leukocytes that originate from the common monocyte, macrophage and dendritic cell (DC) precursor (MDP).1 They have been considered to be the circulating precursors for tissue macrophages and DCs; however, many DCs and macrophage cell types (for example, lymphoid organ DCs, plasmacytoid DCs (PDCs), skin Langerhans cells and brain microglia) originate from the MDP independently of monocytes,1,2 and in some cases even develop independently from the bone marrow.3 Recent experimental evidence rather indicates that monocytes are innate effectors of the inflammatory response to microbes,4 killing pathogens via phagocytosis, the production of reactive oxygen species (ROS), nitric oxide (NO), myeloperoxidase and inflammatory cytokines. In some circumstances they can trigger and polarize T-cell responses4,5 and may also contribute to tissue repair and neovascularization. 6 In addition, monocytes can both stimulate and suppress T-cell responses in infectious and autoimmune diseases.4,5,7 In this issue of Immunology & Cell Biology, Harper and colleagues8 suggest that naı¨ve monocytes can inhibit T-cell proliferation in vitro,