Definition of Monocyte

Monocyte: A white blood cell that has a single nucleus and can ingest (take in) foreign material. (In other words, a monocyte is thus a mononuclear phagocyte that circulates in the blood.)

Monocytes later emigrate from blood into the tissues of the body and there differentiate (evolve into) into cells called macrophages which play an important role in killing of some bacteria, protozoa, and tumor cells, release substances that stimulate other cells of the immune system, and are involved in antigen presentation.