Monocyte is a type of leukocyte, part of the human boy's immune system. Monocytes have two main functions in the immune system: (1) replenish resident macrophages and dendritic cells under normal states, and (2) in response to inflammation signals, monocytes can move quickly (aprox. 8-12 hours) to sites of infection in the tissues and derive into macrophages and dendritic cells to elicit an immune response. Monocytes are usually identified in stained smears by their large bilobate nucleus.