Most of the lymphocytes that circulate in healthy dogs, cats, and horses are small
(mature) cells that have round nuclei with smooth, dense chromatin and a small rim of
blue cytoplasm. These are sometimes confused with nucleated RBCs.
Some lymphocytes, as illustrated by the equine lymphocyte, are slightly larger and have a finer,
looser chromatin pattern. The lymphocytes found in blood of normal ruminants are quite
variable in appearance. Many are large lymphocytes, as shown in the right middle panel,
with loosely clumped chromatin and fairly abundant cytoplasm.
So-called "reactive" lymphocytes are larger cells with coarse (mature) chromatin, and deep blue cytoplasm as shown in the bottom left panel. Lymphocytes with these characteristics are sometimes called immunocytes and are associated with an immune response. These are fairly common in blood of young animals, especially ones that have been recently vaccinated. Another type of lymphocyte that is found in low number in healthy animals is the granular lymphocyte, shown in the bottom right panel. Granular lymphocytes are distinguished by the presence of small pink granules collected into one area of the cytoplasm. Not all lymphocytes in blood smears are round. Some are distorted into other shapes by the mechanical forces applied to them during smearing and some are molded by contact with red cells. |
Last updated on Sunday, March 03, 1996