They are associated with abnormal states, especially bacterial infection, inflammation or tissue necrosis. Several features of the cell are characteristic of a monocyte and serve to distinguish it from a reactive lymphocyte. The nucleus has the reniform or kidney-bean shape commonly present in these cells. The homogeneous cytoplasm is gray-blue and contains vacuoles and a few granules. These cells are easily recognized by their bright orange-red spherical cytoplasmic granules.
Eosinophils typically have a bilobate nucleus separated by a thin filament.
Non-reactive and reactive lymphocytes are differentiated by their morphologic features. Reactive lymphocytes usually have round or oval nuclei and more abundant, pale blue to basophilic cytoplasm. They may have nucleoli. The cell depicted in this photomicrograph has scant cytoplasm and no nucleolus.