Monocytes: a type of white blood cell that help your body fight infections and clean up damaged tissue. They play a key role in the immune system by engulfing bacteria, viruses, and dead cells. Normal monocyte levels indicate your immune system is functioning well. Low monocytes (monocytopenia) are uncommon but may occur with certain infections or bone marrow problems. High monocytes (monocytosis) can occur with chronic infections, inflammation, or recovery from an acute infection.