The diverse roles of monocytes in inflammation caused by protozoan parasitic diseases.

The mononuclear phagocyte system (MPS), comprising monocytes, macrophages, and dendritic cells (DCs), plays an important role in the control of disease, but can also contribute to the establishment of persistent infections. Monocytes are derived from progenitors in the bone marrow. Once in circulation, they migrate into the tissues, differentiate into macrophages, and phagocytose microbes under inflammatory conditions. However, recent work shows they not only act as phagocytes, but are also precursors for particular types of DCs, inflammatory macrophages, and tissue macrophages. The role of monocytes during inflammation in models of bacterial and viral infections, cancer, atherosclerosis, and autoimmunity has been widely studied and reported. In this review we focus on the less understood role of monocytes in protozoan infections.