Corpus: Lymphocyte

Lymphocytes are a subgroup of leukocytes. Their main task is the targeted defence against foreign substances, especially infectious agents. However, their activity is also directed against altered endogenous cells, e.g. tumour cells.

The precursor cells of lymphocytes originate from the bone marrow, further development takes place in the lymph nodes, spleen and other lymphatic organs. They also enter the blood via the lymphatic vessels and migrate into other tissues.

"Naive" lymphocytes that have had no antigen contact predominate in the blood smear. They are referred to as typical lymphocytes or standard lymphocytes. In the Pappenheim stain, they appear as 8-10 μm diameter cells with a large nucleus and a narrow, light basophilic cytoplasmic rim. The nuclear diameter is about the same size as a normal erythrocyte. The chromatin appears heterogeneous and cloddy.

In addition to the standard lymphocytes, granulated lymphocytes are also found in the blood smear. They are also known as LGL cells ("large granular lymphocytes"). These are NK cells or cytotoxic T cells. They normally make up a maximum of 10% of the lymphocytes. They are slightly larger than standard lymphocytes and have a slightly wider cytoplasmic rim with punctate azurophilic granules.

...according to function[Bearbeiten]

• B lymphocytes (B cells): They mature in the MALT and in the lymph nodes and produce specific antibodies against foreign antigens. They can be further subdivided into naive, i.e. antigen-inexperienced B cells, plasmablasts, plasma cells and memory B cells.
• T lymphocytes (T cells): They mature in the thymus and directly recognise foreign cells. Subtypes include naive T cells, T killer cells, T helper cells, regulatory T cells and T memory cells.
• In addition to these two main classes, there is another type of lymphocyte, the NK cells. They have neither a T-cell nor a B-cell receptor.

The lymphocytes of the peripheral blood can be analysed more precisely in the laboratory by means of lymphocyte differentiation.

...according to localisation[Bearbeiten]

• Intraepithelial lymphocytes (IEL)

A pathological increase in lymphocytes is called lymphocytosis, a pathological decrease is called lymphopenia.

• "Lymphocytes" courtesy of the company Sysmex