The image is a microscopic field from a CSF cytospin. The red arrow points to a monocyte and the blue arrow points to a lymphocyte. The lymphocytes in this field have a more regular cytoplasmic border without the cytoplasmic blebbing and pseudopods that are present in monocytes. Monocytic cells seen in body fluids have variable morphology as they have the ability to transform into phagocytic macrophages.
Observe the differences in the cytoplasm between the two cell types. Both cells have blue cytoplasm; however, the monocyte (red arrow) has a grainy, gritty texture that is absent in the lymphocyte (blue arrow). In addition, there are fine red cytoplasmic granules present in the monocyte that are not apparent in the lymphocytes.
Notice the relatively regular nuclear shape of the lymphocytes versus the more complex nuclear shape of the larger monocyte. There is also a difference in the texture of the chromatin between the two cell types. The lymphocyte chromatin is denser and clumped.