Lymphopoiesis

Lymphopoiesis (lĭm'fō-poi-ē'sĭs) (or lymphocytopoiesis) is the generation of lymphocytes, one of the five types of white blood cell (WBC). It is more formally known as lymphoid hematopoiesis.Side by side. Comparing the new and old lineage models.Revised Lineage Myelo-lymphoid flowchart.Blood cell lineage. For scale, note that megakaryocytes (50-100 μm) are 10 to 15 times larger than a typical red blood cell.Blood cell lineage. Based on self-renewal ability.Schematic view. Well-defined lineages.Side by side. Comparing the new and old lineage models. Lymphopoiesis (lĭm'fō-poi-ē'sĭs) (or lymphocytopoiesis) is the generation of lymphocytes, one of the five types of white blood cell (WBC). It is more formally known as lymphoid hematopoiesis. Pathosis in lymphopoiesis leads to any of various lymphoproliferative disorders, such as the lymphomas and lymphoid leukemias. Lymphocytes are considered to be of the lymphoid lineage as opposed to other lineages of blood cells such as the myeloid lineage and the erythroid lineage. Nomenclature, the system of naming things properly, 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 WBC - 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. The partial loss of or loss of function of any white blood cell type is a serious health matter and lymphopoiesis is absolutely necessary for life. 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 life by cell division and differentiation from cells such as common lymphoid progenitors (CLPs) in mice. Were this system to fail, the body would be largely undefended from infection. The set comprising CLP cells and similar progenitors are themselves descendants of the pluripotential hemopoietic stem cell (pHSC) which is capable of generating all of the cell types of the complete blood cell system. Despite their remarkable ability to generate the complete suite of lymphocytes, most progenitors are not true stem cells, however, and must be continually renewed by differentiation from the pHSC stem cell.