Lymphopoiesis (lĭm'fō-poi-ē'sĭs) (or lymphocytopoiesis) is the generation of lymphocytes, one of the five types of white blood cells (WBCs). It is more formally known as lymphoid hematopoiesis. Disruption in lymphopoiesis can lead to a number of lymphoproliferative disorders, such as lymphomas and lymphoid leukemias Terminology Lymphocytes are of the lymphoid (rather than the myeloid or erythroid) lineage of blood cells. Nomenclature is not trivial in this case, because, although lymphocytes are found in the bloodstream and originate in the bone marrow, they principally belong to the separate lymphatic system which interacts with the blood circulation. Lymphopoiesis is now usually used interchangeably with the term "lymphocytopoiesis" - the making of lymphocytes - but other sources may distinguish between the two, stating that "lymphopoiesis" additionally refers to creating lymphatic tissue, while "lymphocytopoiesis" refers only to the creation of cells in that tissue. It is rare now for lymphopoiesis to refer to the creation of lymphatic tissues. Myelopoiesis refers to 'generation of cells of the myeloid lineage' and erythropoiesis refers to 'generation of cells of the erythroid lineage' etc., so parallel usage has evolved in which lymphopoiesis refers to 'generation of cells of the lymphoid lineage'. Observations on research going back well over 100 years had elucidated the two great classes of WBCs - myeloid and lymphoid - and great advances in medicine and science have resulted from these studies. It was only natural to ask where these two great classes of cells arose, and after much work two cell types with some strong stem cell properties were isolated and defined - CMP, the common myeloid progenitor and CLP, the common lymphoid progenitor for mice. But science is an additive game and it was eventually found these progenitors were not unique, and further that the two great families of myeloid and lymphoid were not disjoint, but rather two partially interwoven family trees. This is more than just nomenclature, it is new science that provides challenges of complexity yet offers new vistas of bio-science and the promise of early enhancement of private and public health issues. And it gives insight into the nature of redundancy and overlap in the immune system and hints how to use this to advantage. Purpose Mature lymphocytes are a critical part of the immune system that (with the exception of memory B and T cells) have short lives measured in days or weeks and must be continuously generated throughout