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Lymphopoiesis refers to the generation of lymphocytes, or lymphoid hematopoiesis.

It is sometimes used interchangeably with the term "lymphocytopoiesis", but other sources distinguish between the two, stating that "lymphopoiesis" refers to creating lymphatic tissue, while "lymphocytopoiesis" only refers to the creation of cells in that tissue.

The common lymphoid progenitor differentiates into lymphocytes by first becoming a lymphoblast. It then divides several more times to become a prolymphocyte that has specific cell-surface antigens unique to a T cell or B cell. The common lymphoid progenitor can also differentiate into natural killer cells (NK) and dendritic cells (which are indistinguishable from those derived from myeloid progenitor; however, since there are more common myeloid progenitors than there are common lymphoid progenitors, the majority of the dentritic cells in the body develop from common myeloid progenitors).[1] T and B lymphocytes are indistinguishable histologically but are distinguishable in the location of their differentiation. Indeed, the inactive B and T cells are so featureless with few cytoplasmic organelles and mostly inactive chromatin that until the 1960's textbooks could describe these cells, now the central focus of immunology, as having no known function.[2] T cells are formed in bone marrow then migrate to the cortex of the thymus to undergo maturation in an antigen-free environment for about one week where a mere 2-4% of the T cells succeed. The remaining 96-98% of T cells die by apoptosis and are phagocytosed by macrophages in the thymus. So many thymocytes (T cells) die during the maturation process because there is intensive screening to make sure each thymocyte has the ability to recognize self-peptide:self-MHC complex (major histocompatibility complex) and for self tolerance. Upon maturity, there are several forms of thymocytes including T helper (needed for activation of other cells such as B cells and macrophages), T cytotoxic (which kill virally infected cells), T memory (remember antigens previously encountered), and (arguably) T suppressor cells (which moderate the immune response of other leukocytes). B cells are formed and mature in bone marrow. These cells then leave the bone marrow and migrate to peripheral lymphoid tissues, such as a lymph node. Once in a secondary lymphoid organ the B cell can be introduced to an antigen that it is able to recognize. Through this antigen recognition and other cell interactions it becomes activated and becomes a plasma cell. This B cell end product is an antibody secreting cell that helps protect the body. NK cells, which lack antigen specific receptors, develop in the bone marrow and circulate in the blood until they recognize and kill abnormal cells such as cancer or virally infected cells.

Stages of development

References

  1. ^ Janeway,et al. Immuno Biology, The Immune System in Health and Science.Garland Science Publishing, New York, NY. 2005. ISBN 0-8153-4101-6
  2. ^ Janeway,et al. Immuno Biology, The Immune System in Health and Science.Garland Science Publishing, New York, NY. 2005. ISBN 0-8153-4101-6

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