LYMPHOCYTES
The upper image shows a nucleated cell whose size is similar to that of a red blood cell. It is a leukocyte.
Its nucleus has dense chromatin (is well stained), and spherical. It is not subdivided into lobes, therefore it is not a polymorphonuclear leukocyte, which rules out the diagnosis of a neutrophil, eosinophil, and basophil.
There is very little cytoplasm around the nucleus – only a thin layer. It consists of a light blue rim.
In addition, no specific granules are observed in the cytoplasm – there are no neutrophilic, eosinophilic, or basophilic granules. This confirms that it is not a granulocyte leukocyte, but an agranulocyte.
Agranulocytes are either lymphocytes or monocytes.
A small agranulocyte with very little cytoplasm can only be a a lymphocyte. Monocytes are much larger cells with a lot of cytoplasm.
The cell in the lower figure: same featutes, same diagnosis. Observe that its cytoplasm is not as bluish as that of the lymphocyte of the upper figure. Probably a staining defect as pointed out at the beginning of this chapter.
Blood smear. Staining: Leishman. Large magnification.
Blood smear. Staining: Leishman. Large magnification.