3.1 We need to understand haemopoiesis so we can recognize and treat those conditions in which it is aberrant, such as leukaemia and myeloma.
3.2 In the healthy adult, haemopoiesis occurs in the bone marrow, but in the fetus and neonate it may also occur in the liver and spleen.
3.3 The different types of cell in the bone marrow are: the stem cells and their progeny that produce the blood cells (found in haemopoietic tissue); epithelial cells in the sinuses (vascular spaces or pools of blood); cells that support the bone marrow and often produce growth factors, provide energy (adipocytes), supportive ‘scaffolding’ (fibroblasts), and perform ‘cleansing’ activity (macrophages).
3.4 Pluripotent stem cells can self-reproduce and can give rise to any type of unipotent stem cell. The latter cannot self-reproduce and can only give rise to ‘daughter’ stem cells of a particular lineage (such as either myeloid cells or lymphoid cells, but not both).
3.5 The term colony-forming units (CFUs) was originally coined in research, often using animal models of tissue culture (where, in in-vitro/in-vivo experiments, one stem cell gave rise to one CFU-S (S = spleen) visible as a colony of cells on the spleen surface). Blast cells (such as erythroblasts or myelocytes) arise downstream from stem cells and in turn give rise to more mature cells (such as erythrocytes and neutrophils respectively) that eventually pass into the peripheral blood.
3.6 Molecular signals such as interleukins, erythropoietin, thrombopoietin, and colony stimulating factors all promote haemopoiesis.
3.7 The three types of granulocytes are neutrophils, eosinophils and basophils. Each has their own unique pattern of nuclear morphology and granules, the latter taking up different dyes and so appearing as different colours.
3.8 Juvenile platelets and red blood cells (reticulocytes) are both larger than their respective mature cell. In addition, unlike the mature forms, the cytoplasm of both juvenile types contains messenger RNA, which can be detected with special stains.
3.9 T lymphocytes must pass through the thymus to complete their maturation. The equivalent organ for the final maturation of B lymphocytes has not been defined. It is unclear whether or not NK cells need to pass through a defined organ to complete their maturation.
3.10 The principal reasons for examining the bone marrow are to help confirm or deny a possible diagnosis (such as a leukaemia or megaloblastic anaemia), and also to test the efficacy of therapy (such as chemotherapy for leukaemia).
3.11 A bone marrow aspirate tells us about the cellular composition (for example, in terms of numbers of myeloid and erythroid cells) of the bone marrow, whereas a trephine tells us of the architecture of the bone marrow, and the structure of the sinusoids and fat cells.
3.12 The most common cytochemical tests are Perls’, myeloperoxidase, Sudan black, neutrophil alkaline phosphatase, acid phosphatase, periodic-acid–Schiff, and esterases.
3.13 The common cell-surface markers used in flow cytometry are CD2, CD3, CD7, CD10, CD13, CD19, CD22, CD33, CD34 and CD117. These are used to define different cell populations, for example, in confirming the particular basis of a leukaemia in being of B-lymphocyte or T-lymphocyte lineage.