Monocytes

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In the image above, the upper leukocyte is a monocyte and the lower one is a neutrophil. Monocytes are larger than neutrophils, the nuclei are not as lobated but are quite variable in shape (compare with previous image), and the cytoplasm is generally gray, allowing the lysosomes to appear white. The white lysosomes in the gray cytoplasm may make the cytoplasm appear frothy. See image below for a close up of a monocyte. Monocytes that have migrated through diapedesis into the tissues are then known as macrophages.  

monocyte