What are "atypical" lymphocytes?
Atypical lymphocytes have been observed in the peripheral blood of patients in a large number of clinical situations.
Although lymphocytes are always present in the blood stream, certain viral infections create an environment in which abnormal lymphocyte is produced.
An abnormal lymphocyte has more cytoplasm and thus grows larger in size than a normal lymphocyte as a reaction to infection, hormone production, radiation or other factors that influence the immune system.
Some pathogens that influence the presence of this type of lymphocyte in the blood will also cause this altered cell to take on defining characteristic such as changes to the shape of the nucleus and the colour and quantity of the cytoplasm in the lymphocyte.
These cells are readily identified by their increased size and presence of active DNA synthesis. They closely resemble lymphocytes transformed into blasts by exposure to mitogens and antigens in vitro.
They vary in morphological, detail as well as surface marker characteristics. This indicates that they comprise a heterogeneous mixture of cell types. These data suggest that atypical lymphocytes may represent a polyclonal immune response to antigen stimulation.