Transmission electron micrograph of monocyte and red cells; note bilobed nucleus, granules, organelles. Monocytes are a type of white blood cell or leukocyte. They are the largest type of leukocyte and differentiate into macrophages, dendritic cells and foam cells. As a part of the vertebrate innate immune system monocytes also influence the process of adaptive immunity. Magnification @ 25,000x, 6x7 print.