What are lymphocytes?
Lymphocytes are a subgroup of white blood cells (leukocytes). They include the B lymphocytes (B cells), the T lymphocytes (T cells) and the natural killer cells (NK cells).
Lymphocytes are formed in the lymph nodes, spleen, thymus and bone marrow. The majority of the cells remain there even after they have been formed; only about four percent of the lymphocytes that are formed enter the bloodstream.
What are the functions of lymphocytes?
B lymphocytes develop into so-called plasma cells after contact with foreign substances such as pathogens and produce specific antibodies against the invader.
T lymphocytes and their subtypes, on the other hand, have other defense functions.
- They regulate the immune system’s response to pathogens.
- They fight infected or degenerated body cells (cytotoxic T cells, T killer cells).
- They promote the development of B cells.
- They indirectly support the maturation of antibodies.
In addition, T lymphocytes are involved in the hypersensitivity reaction in contact allergies.
T lymphocytes are also known as memory cells: Once they have made acquaintance with an antigen (characteristic component of a foreign substance), they can immediately identify it upon renewed contact and initiate a rapid specific defense reaction.
What are atypical lymphocytes?
In the context of various diseases, the appearance (morphology) of lymphocytes changes. For example, they become larger, or the cell nucleus changes its shape. Physicians refer to such altered cells as atypical lymphocytes. They are found in the blood in, among others:
- certain forms of toxoplasmosis
- Rubella
- Liver inflammation (hepatitis)
- Mononucleosis (Pfeiffersches glandular fever, infection with the Epstein-Barr virus)
- Cytomegalovirus (infection with the cytomegalovirus, CMV)
Lymphocytes: normal values
In the small blood count, only the total number of leukocytes is given. However, if the physician wants to know the percentage of lymphocytes and the other subgroups of leukocytes, he orders a differential blood count. There, the amount of lymphocytes is usually given as a relative value, i.e. as a proportion of the total leukocyte count (in percent). Sometimes, however, laboratory results also show an absolute value, i.e. the lymphocyte count per nanolitre of blood. Depending on age, the following standard values apply:
|
relative value (proportion of total leukocytes) |
absolute value (number of lymphocytes per nanolitre) |
|
|
< 2 years |
40 – 70 % |
2 – 17 / nl |
|
2 to 5 years |
20 – 70 % |
1.7 – 5.9 / nl |
|
6 to 16 years |
20 – 50 % |
1 – 5.3 / nl |
|
from 17 years |
20 – 45 % |
1 – 3.6 / nl |
When are the lymphocytes elevated?
Increased lymphocyte levels are also found in adults during the healing phase after infections. This is particularly true of viral infections such as mumps or measles, but also of bacterial infections such as whooping cough. Chronic infectious diseases such as tuberculosis or syphilis (lues) also increase lymphocyte levels.
However, lymphocytes can also be too high in diseases that are not caused by a pathogen. Examples of such diseases are:
- chronic inflammatory bowel diseases such as Crohn’s disease or ulcerative colitis
- vascular inflammations (vasculitides) such as giant cell arteritis
- serum sickness (a severe allergic reaction of the immune system)
- hormonal disorders such as Addison’s disease or hyperthyroidism
A particularly pronounced lymphocytosis is found in chronic lymphocytic leukemia (CLL). In this form of blood cancer, the values often rise to over 100,000/ml.
When are the lymphocytes decreased?
If the lymphocytes are too low, this is called lymphopenia or lymphocytopenia. It occurs in the following cases:
- Stress reactions
- therapy with corticosteroids (“cortisone”)
- endogenous increased secretion of corticosteroids
- after radiation therapy
- systemic lupus erythematosus
- diseases of the lymphatic system such as lymph node tuberculosis or non-Hodgkin’s lymphoma (a form of lymph node cancer)
