Monocytes are a population of circulating white blood cells with the potential to differentiate into tissue macrophages and dendritic cells (DCs). Monocytes are derived from precursors in the bone marrow and can be subdivided into subsets that differ in size, trafficking and innate immune receptor expression. Monocytes mediate host antimicrobial defense and are also implicated in many inflammatory diseases, including atherosclerosis.
In addition, monocyte-like cells can be recruited to tumor sites and inhibit tumor-specific immune defense mechanisms. In both mice and humans, monocytes display some typical morphological features, such as irregular cell shape, oval- or kidney-shaped nuclei and cytoplasmic vesicles. However, they are still very heterogeneous and difficult to distinguish from other cells just by morphology or light scatter analysis.