In the blood of healthy people, we see two types of lymphocytes: the standard lymphocyte and the large granular lymphocyte (LGL).


Standard lymphocytes


These are a small cells with a diameter of maximally 1.5 fold the diameter of an erythrocyte. The basophil cytoplasm consists of a narrow margin.

Normal range:
The normal lymphocyte count lies between and x 109/L. Therefore, they are the second most frequent leukocyte in the blood film after neutrophilic granulocytes. If the lymphocyte count is low, lymphopenia is present. If it is increased, then lymphocytosis is present. Morphologically, B and T lymphocytes cannot be distinguished from one another.

Lymphocytes participate in cellular and humoral defense against  infection.

Clinical Significance:
Lymphocytosis may occur primarily in the case of lymphoproliferative syndromes or secondarily, i.e. reactively, in the case of infections (e.g. pertussis, mononucleosis, and other viral infections), stress (e.g. myocardial infarct) and chronic inflammatory diseases.
Lymphopenia can occur in cases of infections (e.g. HIV, tuberculosis), radiotherapy and systemic diseases as well as  during immune suppressive therapy.


Large granular lymphocytes

The large granular lymphocytes are medium sized with a oval, dense nucleus and an excentric, light basophil cytoplasm with clear azure granules. They constitute 5-10% of all lymphocytes. They correspond to either a subpopulation of T-cells or natural killer cells (NK cells).