Lymphocytes are the second most numerous group of leukocytes in a normal blood count, after neutrophils. There are several types and subtypes of lymphocytes. However, they cannot be distinguished from one another in routine histological sections. Identifying specific lymphocyte populations usually requires special techniques, such as immunocytochemistry, which uses antibodies to detect specific cellular markers.
Lymphocytes perform several important functions in the immune system. Among other roles, they recognize specific antigens, produce or contribute to the production of immunoglobulins (antibodies), and initiate and regulate immune responses.
Lymphocytes are small, spherical cells, usually aboutg about 7 µm in diameter. They are mononuclear leukocytes, meaning that their nucleus is not divided into lobes. The nucleus is also approximately spherical and occupies most of the cell. As a result, only a thin rim of cytoplasm is usually visible around the nucleus.
The nucleus of a lymphocyte stains strongly in routine histological preparations because it contains a large amount of condensed chromatin. Therefore, lymphocytes are usually recognized in both histological sections and blood smears primarily by the characteristic appearance of their nuclei.
Look at the two lymphocytes in the figure. Observe their round, strongly stained nuclei, which occupy most of each cell. In both lymphocytes, a very thin rim of cytoplasm can be seen surrounding the nucleus.
More lymphocytes in the next pages as well as in pages 12-14 and 12-15 by clicking on the links page 12-14 and page 12-15.
