Haematopoiesis To describe the components of normal blood, their relative proportions and their functions Blood 8% of body weight Plasma (55%) clear, 90% water, contains salts, enzymes, proteins WBCs and platelet (1%) RBCs (45%) bioconcave– disc, no nucleus = anuclear- 120days lifespan Immature = blasts– Mature= cytes In white blood cells myeloblast goes to neutrophils, basophils, eosinophils Monoblast= monocyte can also become dendritic cells and macrophages – White blood cells (leukocytes)– Polymorphonuclear= neutrophils, eosinophil s, basophils Mononuclear= lymphocytes= T cells, B cells and’ monocytes Lymphoid= NK cells, T-Lymphocyte, B-lymphocyte Myeloid= Monocyte, erythrocyte, neutrophils, basophils, eosinophils, mast cells, megakaryocyte, mast cells BOTH Dendritic cells (from monocyte in myeloid) (lymphoid precursor) Neutrophil – protection from bacteria and fungi Eosinophil- protection against parasites Basophil – increase during allergic reactions Lymphocytes – T cells- protection against viruses, B cells immunoglobulin synthesis Monocyte- protection from back bacteria and fungi phagocytosis – How do blood go from bone to blood vessels? – The bones are perfused with blood vessels- How do we investigate blood? In venepuncture, the superficial veins of the upper limbs are selected and hollow needle is inserted through the skin into the veins. Blood is then collected into evacuated tubes. These veins are present in numbers and are easily accessible. Anticoagulant, EDTA is used to stop blood clotting 1.Using Automated the sample full collected…. blood count Whole blood for a FBC is usually taken into an EDTA tube to stop it from clotting. The blood is well mixed and put through a machine called an automated analyser, counts the numbers and size of RBC and platelets within the blood using sensors Reticulocyte Assessing the young RBCs numbers performed by automated cell counters give indication of output of young RBC by bone marrow – 2. Coulter Principle – electrical impedance Means of counting cells. Whole blood is passed between 2 electrodes through a single cell aperture. Electrical impedance changes as a cell passes through aperture. Change in impedance is proportional to cell volume, resulting in a cell count and measure of volume. 3. Flow Cytometry The cells must be in a single cell suspension with minimal aggregation Passage of cells in single file in front of a laser. The degree to which the laser is interrupted. Its position indicates its forward scatter (FSC) intensity value (cell size), and its side scatter (SSC) intensity value (cell granularity) 4. CD molecules Cluster differentiation is used to identify cells surface proteins provides targets for immune-phenotyping (technique used to study cell surface expressed by cells). Cell surface proteins can differentiate one cell type form another. Flurochrome labelled monoclonal antibodies are directed towards these molecules and thus identify cell types using flow cytometry Blood film – after blood count Thin feathered’ edge of blood smeared on a glass microscope slide and then stained to allow the various blood cells to be examined microscopically. Commonest stain used is MGG ‘ Bone marrow biopsy Patient put into Lateral position- Sample of your solid bone marrow tissue, taken from the back of the hip-bone (pelvis). Small incision made, then hollow needle is inserted through the bone and into the bone marrow. Using a syringe attached to the needle, withdraw a sample of the liquid portion of the bone marrow. 2 samples: Aspirate= liquid found in the bone, to assess the later stages of maturation of haemopoietic cells Trephine= sample of harder bone marrow tissue, provides a core of bone and bone marrow architecture Definition of Haemopoiesis - Erythropoiesis: RBC formation (KIDNEY) - Myelopoiesis; WBC formation (STROMAL CELLS) - Thrombopoiesis: platelets (LIVER) Where does hematopoiesis occur in the body? Embryo is attached to the yolk sac. The yolk sac is a membrane outside the embryo responsible for embryo’s circulation. First few weeks of gestation: blood formation happens in the yolk sac. 6 weeks to 6-7 months of foetus: spleen, liver 6-7months onwards: bone marrow as the main source of hematopoiesis Site of haemopoeisis Infancy all the bone marrow is haemopoietic Childhood- bone is replaced by fatty, adipose marrow Adult- confined– to central skeleton and proximal (closest to body) ends of femurs and humerus o 50% fat in these areas bone marrow becomes yellow o Expansion of haemopoeisis down the long bones occur in bone marrow malignancies - leukaemia– or when there is increased demand - chronic haemolytic anaemia o Capable of reverting to haemopoiesis also liver and spleen can resume fetal haemopoietic role called extramedullary haemopoiesis when there is marrow replacement myelofibrosis OR excessive– demand - severe haemolytic anemia such as thalassemia major. – Haemopoietic stem cells Asymmetrical cell division allows: o Self-renewal: give rise to new stem cells o Pluripotency: give rise to all different blood cell lineage Some pluripotent stem cells differentiate into precursor cells that are at least partially committed to become one type of mature blood cell. RARE: (1 in every 20 million nucleated cell) Many are dormant - only enters cell cycle every 20 weeks Exact phenotype is unknown CD34+, CD38- Located in niches either endosteal (lined by osteoblasts bone lineage), vascular (lined by endothelium- blood lineage) – Bone marrow microenvironment– : surrounded by stromal– cells to form the ECM and growth factors for stem cell survival Amplification With aging number of HSC falls, accumulate mutations Stromal cells of– the marrow: fibroblasts, endothelial cells, macrophages, fat cells have adhesion molecules that react with corresponding ligands on the stem cells to maintain their viability and to localize correctly. Mesenchymal cells are essential in stromal cell formation. They provide the adhesion molecules and cytokines for support. There are two types of bone marrow: Red, or hematopoietic o Produces red blood cells, white blood cells and platelets o Red comes from haemoglobin in the erythroid cells o Hematopoietic cells mature and migrate to enter the circulation when they are formed. o Highly vascular Yellow, or mesenchymal/stromal o Produces fat, cartilage, and bone o Yellow comes from carotenoids in the fat droplets o Lack of vasculature Both yellow and red bone marrow have small/large vessels and veins running through them- the blood supply is delivered to the endosteal cavity by nutrient arteries, then flows through the marrow sinusoids to small vessels that ramify through the cortex. HSC progenitors – (unlike stem cells)- AFTER HSC Lost capacity for self- renewal Irreversibly committed to a specific lineage CFU colony forming unit is the earliest seen cells –under the microscope Self-renewing HSC give rise to several multipotent progenitors (colony forming units (CFU), common myeloid progenitor (CMP) and common lymphoid progenitors (CLP)), which, in turn, produce oligo-potent progenitors, uni-potent progenitors and eventually fully differentiated cells. The stem cell has the capability for self renewal so that marrow cellularity remains constant in a normal healthy steady state. The precursor cells are capable of ‐responding to haemopoietic growth factors with increased production of one or other cell line with the need arises. How is lineage determined? Expression of transcription factors SCL, GATA-2, NOTCH-1: regulate survival of stem cells PI.1, CEBP: commit cells to myeloid lineage GATA-1, FOG-1: roles in erythropoietin and megakaryocytic differentiation 3 major pathways Dimerization of the receptor leads to activation of a complex series of intracellular signal transduction pathways: JAK/STAT MAP Kinase PI3 pathway External signals such as growth factors are involved Haemopoietic growth factors (HGF)- glycoprotein hormones - Stromal cells are the main source of growth factors except erythropoietin comes from kidney and thrombopoietin comes from liver - HGF are glycoprotein - Growth factors affects more than one lineage - GF act mainly on primitive cells/ progenitor cells but can later act on already committed to a particular lineage - Has both additive and synergistic effects - GFs affect the function of the mature cells - Binding of GF with its surface receptor on the haemopoietic cell activates signal transmitted to the nucleus by a cascade of phosphorylation reactions - TF in turn activates/inhibits gene transcription. The signal may: o Enter cell cycle (replicate) o Differentiate o Maintain viability (inhibition of apoptosis) o Increase functional activity - Disturbances of these pathways due to acquired genetic changes: mutations, deletions, translocation involving TF, underlie malignant disorders of the bone marrow like acute/chronic leukaemia and lymphomas Multiple actions: proliferation, differentiation, maturation, activation, and suppression of apoptosis Act on stromal cells: - IL-1, TNF Act on pluripotent stem cells: - SCF, FLT3-L, VEGF Act on multiple progenitor cells: - IL-3, GM-CSF, IL-6, G-CSF, thrombopoietin Act on committed progenitor cells: - G-CSF, M-CSF, IL-5, erythropoietin, thrombopoietin G-CSF (granulocyte colony-stimulating factor- glycoprotein that stimulates bone marrow to produce granulocytes and stem cells to release them into the bloodstream) to produce neutrophils in chemo, erythropoietin to kidney failure, anemia, cancer patients to stimulate erythrocyte drive