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

Introduction Life span Life span  Granulocytes  Erythrocytes  Platelets  Lymphocytes Derived from Stem cells Derived from Stem cells .01% -.05% of the marrow cells

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

Cell hierarchy (Haemopoiesis schematic representation)

Sites of Haemopoiesis Yolk sac Yolk sac Liver and spleen Liver and spleen Bone marrow Bone marrow –Gradual replacement of active (red) marrow by inactive (fatty) tissue –Expansion can occur during increased need for cell production

Stem cells Self-renewal Self-renewal  Normally in G 0 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 Multipotentiality  Capacity to generate cells of all the lymphohaemopoietic lineages

Interaction of stromal cells, growth factors and haemopoietic cells

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

Regulation of Haemopoiesis There should be a balance between cell production and cell death except at the times of requirement There should be a balance between cell production and cell death except at the times of requirement Controlled cell death Controlled cell production

Local and Humoral regulation of Haemopoiesis

Haemopoietic growth factors GM-CSF GM-CSF  Granulocyte-Macrophage colony stimulating factor M-CSF M-CSF  Macrophage colony stimulating factor Erythropoietin 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 Thrombopoietin  Stimulates megakaryopoiesis

Haemopoietic growth factors Cytokines Cytokines  IL 1 (Interleukin 1)  IL 3  IL 4  IL 5  IL 6  IL 9  IL 11  TGF- β  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

Role of growth factors in normal haemopoiesis

Regulation of Haemopoiesis Local environmental control Stromal cell mediated Haemopoiesis Haemopoietic growth factors (Humoral regulation) Apoptosis

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

Mechanism; apoptosis

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

Development of mature red cells

Granulopoiesis Granulocytes Granulocytes –Neutrophils –Eosinophils –Basophils Only mature cells are present in peripheral blood Only mature cells are present in peripheral blood E N B

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

Neutrophil kinetics

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

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

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

Lymphopoiesis

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

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