Formation and development of blood cells. Erythrocytes, platelets, leukocytes (neutrophils, eosinophils, basophils, lymphocytes, monocytes).
Daily output of mature blood cells
200 billion erythrocytes, 100 billion platelets, 50-100 billion granulocytes.
Production sites of hematopoiesis
Begins in yolk sac in embryo, in 3rd mo of gestation stem cells migrate to fetal liver and spleen, and last bone marrow.
Production sites in adult
Bone marrow: Red: hematopoietic tissue (yellow:adipose). All bones in young, flat bonees and epiphyses in older. Pathological: Extramedullary hematopoiesis: spleen, liver, lymph nodes. Blood: few but increased to collect for transplant.
Architecture of bone marrow
Vascular space (separated from hematopoietic by several cell laayers, pores regulate release of BM elements), fat (extravascular), hematopoietic space (extravascular).
Bone marrow cells
Hematopoietic cells, stroma (adipocytes, endothelial cells, smooth muscle cells, osteoblasts, osteoclasts, adventicial reticular cells, fibroblasts)
Pluripotent stem cells-->more stem cells and precursor (partially committed cells)-->mature blood cells
Essential attributes of hematopoietic stem cells
Self renewal, multilineage differentiation, ability to reconstitute hematopoietic system of lethally irradiated host.
Stem cell surface markers
CD34+, lineage specific negative, KIT+, Thy+. Use efflux rhodamine-123 and Hoeschst dyes.
Sources of HSC for investigation and clinical transplantation
Bone marrow, peripheral circulation, umbilical cord blood.
HSC in blood circulation
Few but G-CSF and chemo increase stem cells in blood. Useful for collection/transplantation.
Derivation of HSC
In embryonic development may be derived from hemangioblasts (precursors of HSC and endothelial cells), hemogenic endothelial cells acquiring potential for hematopoiesis.
Fates of HSC
1. Self renewal, 2. differenentiation, 3. apoptosis. Highly regulated by extrinsic and intrinsic cell characteristics.
Self-renewing division possibilities
1. Symmetric (two identical HSC daughter cells) or 2. asymmetric (one daughter cell as HSC and the other differentiates/apoptoses)
Cytokine regulation of hematopoiesis
Growth factors required. About 77 types. Particular lineage may need several cytokines but one may be most important.
IL3 and stem cells
Stimulates stem cell growth, growth of erythroid, myeloid, important for all lineages.
GM-CSF and stem cells
Stimulates granulocyte (neutrophils, eosinophils, and basophils) and monocyte growth
Supports neutrophil and other granulocyte development.
Made in kidney, supports growth of erythroid precursors.
Made in liver. Growth factor for megakaryocyte. May treat thrombocytopenia.
First recognizeable cells in microscope
Erythroblasts, then basophilic cytoplasm and projections, then eosinophilic, cytoplasmic expels nuclei-->mature erythrocytes.
Erythron-proliferating pool of marrow erythroid precursor cells and mass of circulating mature RBC. Low RBC: anemia, high RBC: erythrocytosis/polycythemia
Creates basophils, neutrophils, eosinophils. First precursor is myeloblasts: prominent nucleus, scattered cytoplasm, 2. promyelocyte: biggest cells in lineage, granule development, 3. myelocytes: no nucleolus, round nucleus, granules to size, 4. methamylocyte, kidney shaped nucleus, first visible cells: band cells: C-shaped nucleus, more coarse looking. 5. Segmented nucleus (PMN: 3-5 lobes). In megaloblastic anemia: pathognomonic 7 lobes.
90% in BM, 2-3% in circulation (t1/2 6-7 h), free flowing, marginated. 7-8% in tissues (1-4 days). Host defense against bacterial infection, normally 45-74% of WBC, band 0-4%. Low count: neutropenia, high count: neutrophilia. Immature cells: shift to left.
Susceptible to infection, <1000/mcl, <500/mcl: agranulocytosis, control of endogenous microbial flora impaired, <200 severe: absent inflammatory process.
Causes of depressed production in neutropenia
Drug-induced (chemotherapy, other), hematologic diseases, infections.
Causes of neutropenia peripherally
Autoimmune disorders: increased peripheral destruction, excessive peripheral pooling: hemodialysis.
Increased production, increased marrow release, or defective migration to periphery. >30,000/mcl: leukemoid reaction.
Eosinophils anad basophils
Similar to neutrophils, different types of granules. Mast cells: similar to basophils.
First cell is promegakaryoblasts: large nucleus and nucleolus, small cytoplasm. 2. Megakaryocyte: many lobules and one cytoplasm, 3. Thrombocytes: small particulates of cytoplasm released into circulation. Life span 7-10 days. Lack nucleus, organelles.
Different types of lymphocytes: B, T, NK. Small cytoplasm, nucleus big as in RBC. Maybe granules. Plasma cells come from B-cells. B-cells migrate from bone marrow to lymph nodes, spleen, etc. to become memory or plasma.
Aplastic Anemia definition
Peripheral blood pancytopenia with hypocellular bone marrow: fail to form blood cells of all 3 lineages: anemia (Hb<10g/dl, leukopenia-neutrophils <1.5x10^9/l), thrombocytopenia-platelets <50x10^9/l)
Classification of AA
Congenital: Fanconi Anemia, Disceratosis Congenita. Acquired: Idiopathic, ionizing radiation, drugs/chemicals, viruses.
Aplastic Anemia epidemiology
Rare in Europe, more common in Japan. Same risk for males and females and races in US, males in Far East. Peak age incidence 20-30 and 60. >50% with severe AA may die within 6mos.
Paroxysmal Nocturnal Hemoglobinuria (PNH)
Clonal hematopoietic stem cell disorder. Caused by defect in protein anchor GPI. Result of lack of surface proteins, unable to remain tethered to cell surface proteins. Enhanced sensitivity to complement-mediated cell destruction. Present in 20-25% of AA patients.
Pathogenesis of AA
Direct and indirect bone marrow failure. Circulating activated cytotoxic lymphocytes and increased production of cytokines typical of Th1 response-IFNa, TNFg and IL2. Fas-mediated cell death-->pancytopenia. Increased CD8 lymphocyte.
Clinical manifestations of AA
Pallor, headache, palpitations, dyspnea, fatigue, foot swelling. Thrombocytopenia: mucosal/gingival bleeding/petechial rashes, purpura, ecchymoses. Neutropenia: overt infections (not apparent at diagnosis), recurrent infections, mouth/pharyngeal ulcerations. PE: pallor and tachycardia. Not splenomegaly nor lymphadenopathy common-try other diagnosis.
Diagnosis of AA
Pancytopenia, no splenomegaly, BM: hypocellular, increased fat, no cytogenic abnormalities, no fibrosis, no infiltration by tumor cells.
Differential Diagnoses against AA
Pernicious anemia, MDS, AML, ALL, HCL, lymphomas, myelofibrosis
Usually due to vitB12 or folate deficiency. May present with pancytopenia if severe. Blood smear: macrocytosis with MCV>110, hypersegmentation of neutrophils. BM hypercellular, packed.
Myelodysplastic Syndrome (MDS)
BM: hypercellular (10-20%), precursors of RBC, WBC and megakaryocytes abnormal morphology, cytogenic abnormalities (chr5,7,etc.) Blasts <=20%.
Hairy Cell Leukemia
Hairy lymphocytes on blood and marrow smears. Splenomegaly. Monocytopenia. Dry bone marrow tap.
Fanconi's Anemia (FA)
Most frequently reported of rare inherited bone marrow failure syndromes. >1200 cases reported in med literature. Classic phenotype: pigment changes around neck, shoulders, trunk, short stature, absent radii and absent bilateral thumbs (but not necessarily), microcephaly, low set ears. Autosomal recessive, at least 11 genes including BRCA2. Occurs equally in males and females in all ethnic groups, most by age 12. AML common.
Definitive test for FA
Chromosome breakage test: x-link DNA in test tube, cells cannot correct damage and marked chromosome breakage. Essential to test before BMT for aplastic anemia because prep will be different.
Pancytopenia and BM defects/diagnosis
Rare disorder with 3 groups of symptoms: 1. hypo/hyperpigmentation, 2. progressive nail dystrophy, 3. slow changing mucous membranes (leukoplakia) in anus, urethra, lips, mouth, or eye. AA also frequent. M>F, often x-linked. Supportive treatment (blood transfusion-plt, hematopoietic growth factors, infections), specific treatment (BMT if <40, immunosuppressive therapy). GFs not recommended (elevated). Fever-immediate hospitalization, wide spec a/b.
Clinical triad of PNH
Intravascular hemolysis with hemoglobinuria, venous thrombosis, BM failure