PATHOLOGY OF BONE MARROW Doç. Dr. Işın Doğan Ekici

The blood is a mixture of cellular elements, fluid, proteins and metabolites.

Functions of blood: Respiration, Nutrition, Waste elimination, Thermoregulation, Immune defense, Acid-base balance, Water balance, Internal communication. 3

Blood has four major elements: Red blood cells White blood cells Platelets Plasma- proteinaceaus solution in which cells circulate and carries nutrients, metabolites, antibodies, hormones, proteins of blood clotting system and other molecules.

HEMOPOIESIS The site of blood formation (hemopoiesis) changes several times during fetal development; the earliest sites being the yolk sac and then the liver and spleen at 5 months the fetal bone marrow begins to produce white cells and platelets at 7 months red cell production starts in the marrow

In postnatal life, under normal circumstances, the formation of cellular elements of the blood (hemopoiesis) occurs in the bone marrow.

Bone marrow contains a stromal matrix which provides the correct microenvironment for stem cell growth. Embryo : Yolc Sac Fetus: Spleen/ Liver

Proliferation of the stem and progenitor cells is under control of the hormone-like inducers of growth and differantiation, produced by stromal cells of the microenvironment STROMAL CELLS Macrophages Fibroblasts Reticulum cells Fat cells Endothelial cells EXTRACELLULAR MATRIX Fibronectin Hemonectin Laminin Collagen Proteoglycan (acid mucopolysacharides e.g. chondroitin, heparan)

Blood islands in Yolk sac Liver* Spleen* & lymph nodes SITES OF HEMATOPOIESIS embryonic Blood islands in Yolk sac Liver* Spleen* & lymph nodes Developing bones-Red marrow * * In adult marrow disease*, these organs may again be sites of hematopoietic tissue - ectopic myeloid tissue * e.g., myelofibrosis

HEMOPOIETIC PROGENITOR CELLS All cellular elements of the blood originate from a common pluripotential progenitor stem cell (hemopoietic stem cell-hsc) The main types of multipotential progenitor cell derive from the pluripotential hemopoietic stem cell -lymphoid progenitor cells, which give rise to the different types of lymphocyte (B and Tcells types- -granulocyte/erythroid/monocyte/megakaryocyte (CFU-GEMM or CFU-MIX) which give rise to main types of blood cell

The types of committed progenitor cell derived from the multipotential CFU-GEMM (CFU-MIX) cells are: erythroid (CFU-E), which give rise to red cell precursor cells granulocyte/monocyte progenitor cells (CFU-GM), which give rise to granulocytes and monocytes by forming further subsets of specific progenitor cells (CFC-G and CFC-M) eosinophil (CFU-Eo), which give rise to eosinophils Basophil (CFU-Bas),which give rise to basophils megakaryocytic (CFC-Meg), which give rise to megakaryocytes (and so platelets)

HEMATOPOIESIS Lineages Lymphopoiesis HEMATOPOIESIS Lineages Monocytopoiesis Granulopoiesis stem cell Pluripotent stem cell Erythropoiesis Thrombopoiesis Pro-erythroblast Lymphoblast Monoblast Myeloblast Megakaryoblast Basophilic erythroblast Pro-Myelocyte Polychromatic erythroblast Myelocyte Orthocromatic erythroblast Metamylelocyte Reticulocyte Megakaryocyte Band granulocyte Lymphocyte RBC Platelets Granulocyte Monocyte

{ HEMATOPOIESIS Subdivisions Lymphopoiesis stem Granulopoiesis cell PMN Bas Lym Mon Eos Pla RBC { Lymphopoiesis stem cell Granulopoiesis Monocytopoiesis Myelopoiesis Erythropoiesis Megakaryopoiesis Thrombopoiesis

HEMOPOIESIS The pluripotential stem cells are found in very small numbers in blood cell formation sites and even smaller numbers in the peripheral blood. The pluripotential stem cells divide and give rise to cells with a more retricted line of growth.

Blood cells have limited lifespans, and need to be replaced with precisely matching numbers - Hematocytopoiesis Young replacing cells come, by many divisions and steps of differentiation, from stem cells stem cell HEMATOPOIESIS

STEM CELLS KEEP REPLACEMENT GOING STEM CELLS HAVE TO REPLACE THEMSELVES BY DIVISION, AS WELL AS TO PROVIDE CELLS TO DIFFERENTIATE Symmetric division The two ways this can happen are shown stem cell Asymmetric division

Pluripotential stem cells are capable of forming any type of blood cell, Multipotential progenitor cells are capable of forming a spesific but a wide range of blood cells, Committed progenitor cells are capable of forming only one or two types of blood cell, Maturing cells are undergoing structural differentiation to form one cell type and are incapable of division

THE BONE MARROW The bone marrow is the main site of hemopoiesis-also contains macrophages which remove aged and defective red cells from the circulation by phagocytosis Bone marrow has a highly developed set of vascular sinusoids Bone marrow support cells have important roles in hemopoiesis-fibroblast-like support cells (reticular cells) that synthesize collagenous reticulin fibers, extracellular matrix materials, and certain growth factors.

NORMAL BONE MARROW

GRANULOPOIESIS The formation of granulated white cells is termed granulopoiesis This takes place under the influence of cytokines The first recognizable precursor of neutrophil formation is myeloblast Maturation from myeloblast to neutrophil takes 7-8 days and 5 cell divisions between myeloblast and metamyelocyte stages

After metamyelocyte stage no further multiplication division takes place Mature neutrophils remain in the marrow for 5 days and then released into the blood After circulating for about 6 hrs, they migrate into the peripheral tissues

Granulopoiesis

Neutrophils Production and differantiation: 6-10 days Reserve pool (BM): 10-15 times the circulation Migrate into tissues and perform phagocytic function Survival: 2-4 days

NORMAL LYMPHOCYTE AND NEUTROPHIL

Increase in the number of circulating neutrophils may occur by two mechanisms: A large number of neutrophils , are loosely adharent to the sinusoidal endothelium in the bone marrow, in bacterial infection they are poured into the circulation To maintain a high blood neutrophil count , there is increased proliferation increased proliferation of granulocyte precursors- this is regulated by secretion of cytokines-IL-1, GM-CSF and G-CSF

Neutrophilic Granules Primary granules Acid phosphatase Myeloperoxydase Esterase Secondary granules Aminopeptidase Lysozyme Collagenase

EOSINOPHILS

EOSINOPHIL

BASOPHILS

BASOPHIL

MONOCYTES

MONOCYTE

Monoctes are derived from CFC-M cells under the influence of cytokines They have no reserve pool, they leave the marrow soon after their formation

Lymphocytes

Lymphocytes Assist the phagocytes in the defence Produced in bone marrow from pluripotent cells Two main groups: T-, B- lymphocytes Natural Killer

T-Cell T-cell: 65-80% of circulating lymphoctes

B-Cell 5-15 % of circulating lymphocytes B-cells which have matured and secrete immunoglobulin are termed plasma cells

Natural Killer Non-T, non-B cells. The majority Large granular lymphocytes (LGL) (can kill targets without MHC restriction). Antibody dependent cellular cytotoxic (ADCC) are able to kill tumour and virus-infected cells. (they are also involved in graft rejection)

ERYTHROPOIESIS Erythropoiesis is associated with the formation of distinct precursor cells termed erythroblasts. Red cells are the terminal differentiated progeny of one cell line of pluripotent bone marrow stem cells which is committed to erythropoiesis only

Differentiation of these cells into mature red cells is associated with: decrease in cell size Hb production gradual decrease and eventual loss of all cell organelles changing cytoplasmic staining from basophilia to eosinophilia due to Hb condensation and eventual loss of the nucleus

ERYTHROPOIESIS Red cell formation occurs in small erythroblastic islands consisting of one or two specialized macrophages surrounded by red cell progenitor cells in the marrow When mature, the red cell contacts nearby sinusoidal endothelium and passes out to enter circulation

Control of Erythropoiesis 15

Stimuli for RBC production The kidney, hepatocytes and the interstitial cells of veins produce the hormone erythropoietin. Extrarenal sites of conversion may include some tumors and cysts: leiomyomas, cerebral hemangioblastomas, some renal cysts.

Erythrocytes 18

The bone marrow has three mechanisms at its disposal to respond to an acute decrease in circulating erythrocytes: The marrow can increase the number of cells in the erythroid pool by increasing the number of stem cells that will differentiate into erythrocytes; The marrow can decrease the time it takes for each erythroid cell to reach maturation; or The marrow can release reticulocytes into the bloodstream earlier.

Peripheral blood Leukoerythroblastic smear Causes young red cells and young granulocytes in the bloodstream. Causes agnogenic myeloid metaplasia metastatic carcinoma lymphoma leukemia bone marrow hyperplasia / extramedullary hematopoiesis severe hemolysis.

RBC morphology Hereditary elliptocytosis ("hereditary ovalocytosis") Lack the central pallor of biconcave RBC's Autosomal dominant hemolytic syndrome

SPHEROCYTES

Thalassemia cells tend to be smaller with a higher hemoglobin concentration,

Nucleated RBCs in severe beta-thalassemia

Ring cells Iron stays in normoblast mitochondria Etiology: Alcoholism Drugs (isoniazid, etc) Lead poisoning Pyridoxine responsive anemia Preleukemia ("myelodysplasia").

Fragmented RBC's known as "schistocytes"

Target cells - iron deficiency

Target cells and schistocytes - Hb C disease

RETICULOCYTES

ERYTHROID HYPERPLASIA

NORMAL BONE MARROW

Megakaryocytic hyperplasia

APLASTIC ANEMIA

MEGAKARYOCYTES Megakaryocytes are the largest cells seen in bone marrow aspirates Cytoplasmic maturation involves the elaboration of granules

MEGAKARYOCYTES