Normal Haemopoiesis

1. Normal Haemopoiesis Dr. Tariq M. Roshan Department of Hematology PPSP

2. Introduction Life span Granulocytes Erythrocytes Platelets Lymphocytes Derived from Stem cells .01% - .05% of the marrow cells Every day 1013 myeloid cells must be produced. In steady state the number of cells which are required is equal to the body weight. All these cells are derived from the stem cells. Stem cells are relatively few in number, comprising 0.01% to 0.05% of the marrow cells.Every day 1013 myeloid cells must be produced. In steady state the number of cells which are required is equal to the body weight. All these cells are derived from the stem cells. Stem cells are relatively few in number, comprising 0.01% to 0.05% of the marrow cells.

3. Introduction Stem cells Self renewal Plasticity Progenitor cells Developmentally-restricted cells Mature cells Mature cell production takes place from the more developmentally-restricted progenitors

4. Cell hierarchy (Haemopoiesis schematic representation) Highly simplified diagram to demonstrate the stages of development of various cell types.Highly simplified diagram to demonstrate the stages of development of various cell types.

5. Sites of Haemopoiesis Yolk sac Liver and spleen Bone marrow Gradual replacement of active (red) marrow by inactive (fatty) tissue Expansion can occur during increased need for cell production Embryonic haemopoietic stem cells-mesenchymal cells in yolk sac After 12 week fetal liver and spleen becomes the main site From week 20, bone marrow starts to become important and by the time of birth it is the main haemopoietic organEmbryonic haemopoietic stem cells-mesenchymal cells in yolk sac After 12 week fetal liver and spleen becomes the main site From week 20, bone marrow starts to become important and by the time of birth it is the main haemopoietic organ

6. Stem cells Self-renewal Normally in G0 phase of cell cycle The capacity for self-reproduction is vastly in excess of that required to maintain cell production for normal lifetime As cells increase in number they differentiate as well Multipotentiality Capacity to generate cells of all the lymphohaemopoietic lineages

8. Interaction of stromal cells, growth factors and haemopoietic cells The bone marrow forms a suitable environment for stem cell growth and development. Different factors including macrophage, endothelial cells, fibroblast, extracellular matrix, secrete several factors necessary for stem cell survival.The bone marrow forms a suitable environment for stem cell growth and development. Different factors including macrophage, endothelial cells, fibroblast, extracellular matrix, secrete several factors necessary for stem cell survival.

9. Progenitor cells Encompasses from immediate progeny of stem cells to cells committed to one differentiation lineage Progenitor cells become progressively more restricted in their differentiation and proliferation capacity Late progenitor cells eventually restricted to one lineage

10. Regulation of Haemopoiesis There should be a balance between cell production and cell death except at the times of requirement Cells in the different tissues of the body can signal the need of different levels of cell production e.g anoxic conditions lead to production of erythropoietin The control of cell death by apoptosis is being increasingly acknowledged to be of critical importanceCells in the different tissues of the body can signal the need of different levels of cell production e.g anoxic conditions lead to production of erythropoietin The control of cell death by apoptosis is being increasingly acknowledged to be of critical importance

11. Local and Humoral regulation of Haemopoiesis

12. Haemopoietic growth factors GM-CSF Granulocyte-Macrophage colony stimulating factor M-CSF Macrophage colony stimulating factor Erythropoietin Erythropoiesis stimulating hormone (These factors have the capacity to stimulate the proliferation of their target progenitor cells when used as a sole source of stimulation) Thrombopoietin Stimulates megakaryopoiesis The haemopoeitic growth factors are glycoprotein hormones that regulate the proliferation and differentiation of haemopoietic progenitor cells and the function of mature blood cells. T lymphocytes, monocytes, marcrophages and stromal cells are the major sources of growth factors except for erythropoietin, 90% of which is synthesized in the kidney and thrombopoietin, made largely in liver.The haemopoeitic growth factors are glycoprotein hormones that regulate the proliferation and differentiation of haemopoietic progenitor cells and the function of mature blood cells. T lymphocytes, monocytes, marcrophages and stromal cells are the major sources of growth factors except for erythropoietin, 90% of which is synthesized in the kidney and thrombopoietin, made largely in liver.

13. Haemopoietic growth factors Cytokines IL 1 (Interleukin 1) IL 3 IL 4 IL 5 IL 6 IL 9 IL 11 TGF-ß SCF (Stem cell factor, also known as kit-ligand) Cytokines have no (e.g IL-1) or little (SCF) capacity to stimulate cell proliferation on their own, but are able to synergise with other cytokines to recruit nine cells into proliferation

14. Role of growth factors in normal haemopoiesis

15. Regulation of Haemopoiesis

16. Apoptosis Regulated physiological cell death Homeostasis Morphological evidence Enzymatic digestion of DNA and cell disintegration Caspases Endonuclease Two major pathway of activation of caspases Membrane signalling Cytochrome c release

17. Mechanism; apoptosis

18. Erythropoiesis and erythrocytes Lifespan – 120 days Non nucleated Biconcave disc Production regulated by Epo Needs Fe, B12, folate & other elements for development

19. CFUe the first recognizable cell in this lineage. Large cell with dark blue cytoplasm, central nucleus and nuclei and slightly clumped chromatin. The cytoplasm stains paler blue as it loses its RNA and protein synthesis apparatus and nuclear chromatin becomes more condense. The nucleus is finally extruded from the late normoblast with in the marrow and reticulocyte are formed which still contains RNA and still can synthesize hemoglobin.CFUe the first recognizable cell in this lineage. Large cell with dark blue cytoplasm, central nucleus and nuclei and slightly clumped chromatin. The cytoplasm stains paler blue as it loses its RNA and protein synthesis apparatus and nuclear chromatin becomes more condense. The nucleus is finally extruded from the late normoblast with in the marrow and reticulocyte are formed which still contains RNA and still can synthesize hemoglobin.

20. Development of mature red cells

21. Granulopoiesis Granulocytes Neutrophils Eosinophils Basophils Only mature cells are present in peripheral blood

22. Granulopoiesis Neutrophil 2-5 lobe nucleus Primary or secondary granules Pink (azurophilic granules) Grey-blue granules Life 10 hours Precursors Myeloblast <4% Pro myelocytes Myelocytes Metamyelocytes Band form (stab form)

23. Neutrophil kinetics

24. Eosinophils Coarser & more deeply red staining granules Rarely more than two lobes of nucleus Special role in allergy, inflamation & parasite infection Basophils Occasionally seen Dark cytoplasmic granules Role in hypersensitivity response Give rise to mast cells Granulopoiesis

25. Monocytes Larger than lymphocyte Oval or indented nucleus Monocytes >>>>to macrophage Specific function depends on the tissue type

26. Lymphopoiesis Immunologically competent cells Primary lymphoid organs Bone marrow Thymus Secondary lymphoid organs Lymph nodes Spleen Lymphoid tissues Lymphocytes B and T lymphocytes NK killer cells

27. Lymphopoiesis

28. Thrombopoiesis Platelet play a major role in primary hemostasis Life span 7-10 days Production, fragmentation of cytoplasm Megakaryocytes undergoes endomitotic division 1/3 in spleen

29. Summary Normal haemopoiesis is necessary for the survival It is under the control of multiple factors Normal bone marrow environment is necessary for normal haemopoiesis Decreased production results in cytopenias