Lymphocyte
A lymphocyte is a type of white blood cell involved in the human body's immune system. There are two broad categories of lymphocytes, namely T cells and B cells. Lymphocytes play an important and integral part of the body's defenses.
T cells are chiefly responsible for cell-mediated immunity whereas B cells are primarily responsible for humoral immunity (relating to antibodies). T cells are named such because these lymphocytes mature in the thymus; B cells, named for the bursa of Fabricius in which they mature in bird species, are thought to mature in the bone marrow in humans.
In the presence of an antigen, B cells can become much more metabolically active and differentiate into plasma cells, which secrete large quantities of antibodies.
Microscopically, in a Wright's stained peripheral blood smear, a normal lymphocyte has a large, dark-staining nucleus with little to no basophilic cytoplasm. In normal situations, the coarse, dense nucleus of a lymphocyte is approximately the size of a red blood cell (about 7 micrometres in diameter). Some lymphocytes show a clear perinuclear zone (or halo) around the nucleus or could exhibit a small clear zone to one side of the nucleus.
It is impossible to distinguish between T cells and B cells in a peripheral blood smear. Normally, flow cytometry testing is used for specific lymphocyte population counts. When one must specifically determine the percentage of lymphocytes that produce a particular secretion (say, a specific antibody or cytokine), the ELISPOT or secretion assay techniques can be used instead.
The human immunodeficiency virus (HIV) hijacks and destroys T cells (specifically, CD4+ lymphocytes). Without this key defense, the body is susceptible to opportunistic diseases that otherwise would not kill healthy people.
A lymphocyte count is part of a peripheral complete blood cell count and is expressed as percentage of lymphocytes to total white blood cells counted. An increase in lymphocytes is usually a sign of a viral infection (in some rare cases, leukemias are found through an abnormally raised lymphocyte count in an otherwise normal person). A general increase in the number of lymphocytes is known as lymphocytosis whereas a decrease is lymphocytopenia.
See also
| Blood - Blood plasma - edit |
| Pluripotential hemopoietic stem cell | Red blood cells (Reticulocyte, Normoblast) | White blood cells |
| Lymphocytes (Lymphoblast) |
| T cells (Cytotoxic, Helper, Regulatory T cell) | B cells (Plasma cells & Memory B cells) | Natural killer cell |
| Myelocytes (Myeloblast) |
| Granulocytes (Neutrophil, Eosinophil, Basophil) | Mast cell precursors | Monocytes (Histiocyte, Macrophages, Dendritic cells, Langerhans cells, Microglia, Kupffer cells, Osteoclasts) | Megakaryoblast | Megakaryocyte | Platelets |
The content of this page is retrieved from http://en.wikipedia.org/wiki/Lymphocyte under GFDL
