Cytokines of Hematopoesis 8/22 Flashcards
Hematopoesis in tissues during development
- Yolk-Sac Phase: 3rd week of gestation
- Hepatic Phase: in liver and spleen - during second trimester
- Bone Marrow Beginning the 2nd trimester, becomes the only location in adulthood
Stem Cell Factor (C-Kit Ligand)
- produced by bone marrow stromal cells
- HSC has c-Kit (tyrosine kinase) receptors where it binds SCF (through MAPK, jak/stat pathway)
- Proto-Oncogene
- Signaling of SCF induces self-reneewal and differentiation (directed by probability and environment along with synergistic signals)
Imatnib
an inhibitor of tyrosine kinases with effects in the treatment of chronic myeloid leukemia
- in the presence of imatinib (bound intracellularly to the ATP binding site) a protein substrate is not phosphorylated and signaling cascade is inhabited.
Lineage Restricted Progenitor Cells
Descends of HSC’s in bone marrow
- multipotent, non-renewing
- two types: common myeloid progenitor cells (CMP) and common leymphoid progenitor cells (CLP)
Cellular Elements of blood
all descend from myeloid stem cells
- erythrocytes
- leukocytes
- granulocytes
- agranulocytes
- platelets
Erythrocytes
- RBC’s
Anatomy: Anucleate, biconcave, lacks organelles
Contains: PM, CS, Hemoglobin, Glycolytic Enzymes
Lifespane = 120 days
ABO Blood Groups
- products of glycosylation
- O antigen (default): lacking functional enzyme, no extra sugar
- A Antigen: N-acelylygalactosamine adds an additional N-acetylgalactosamine
- B Antigen: Galactose transferase adds an additional galactose
- AB Blood- group has both enzymes
Erythropoiesis
Location: Bone Marrow, erythrocytes mature in blood stream (last step)
- 10 step process: starts with the Common Myeloid Progenitor (CMP)
- under the influence of cytokines: Erythropoietin (EPO), IL-3 and IL-4
10 steps of erythropoesis (see pictures of staining changes through this process)
- Megakaryocyte/Erythrocyte Progenitor (MEP: bipotential stem cell
- Erythrocyte-committed Progenitor (ErP)- monopotent stem cell)
- Proerthroblast: large nucleus, basophilic staining due to free ribosomes synthesizing hemoglobin
- Basophilic Erythroblast: Large nucleus, basophilic due to free ribosomes
- Polychomatophilic Erythroblast: Large Nucleus, basophilic b/c of ribosomes and also acidophilic (eosin staining) due to hemoglobin produced
- Normoblast: orthochromatophilic erythroblast, dense nucleus, eosinophilic b/c of hemoblobin, no longer capable of dividing
- Reticulocyte: polychomatophilic erthrycotye, anucleate, eosinophilic b/c of hemoglobin, more basophilic than erythrocytes due to some ribosomes still. Reticulocytes remain in marrow for 1-2 days arnd are released into blood stream where they mature into
- erythrocyte
Erythropoietin (EPO)
- stimulates the early stages of the erythroid colony-forming unit (CFU) to proliferate and differentiate into polychomatophilic and orthochromatic erythroblasts.
- produces in the kidneys in response to hypoxia: HIF-1
- when EPO is present there is less apoptosis
EPO Receptor
Expressed by committed erythroid progenitors
- activation is antiapoptotic: normally these cells undergo large amounts of apoptosis
- expressed by proerythroblasts and normoblasts and induces proliferation
Erythropoietin and JAK-STAT Pathway
- EPO produced by IS cells in the renal cortex and is transported to the bone marrow by blood.
- In bone marrow, EPO binds to EPO receptor and induces binding of cystolic STAT 5 protein to JAK2
- the inactive form of STAT5 contains an SH2 domain. STAT5 is recreuited by JAK2 and binds to it, and becomes homodimerized
- Phosphorylated STAT5 translocates to nucleus.
- after binding DNA, the phosphorylated STAT 5 activates the transcription of specific genes required for erythropoeisis.
Recombinant EPO (rHuEPO)
- in chronic kidney disease- reduced EPO production leads to anemia
- chemotherapy- promotes regeneration of RBCs depleted by treatment
- blood doping: can be detected because rHuEPO has a different isolectric point because itis a different isoform
- EPO acts here to induce formation of proerythroblast, primitive/mature progenitor and erythroid CFU
Thrombocytes and their 4 zones
- platelets = small membrane bound cytoplasmic fragments, anucleate
4 zones: - Peripheral Zone: Cell membrane and Glycocalyx (integral membrane glycoporteins, coagulation factors, glycosaminoglycans)
- Structural Zone: cytoskeleton
- Organelle Zone: Mitochondria, peroxisomes, glycogen, granules
- Membrane Zone: Open Canalicular system (OCS, contains remnants of membrane channels that subdivided the precursor megakaryocyte into platelets); Dense Tubular System (storage for calcium ions, originates from RER of precursor)
Thrombopoiesis- Six steps
Location: Bone Marrow
6 steps of platelet Generation:
1) CMP: under influence of cytokines: granulocyte-macrophage colony stimulating factor (GM-CSF) and IL-3
2. Megakaryocyte/Erythrocyte Progenitor (MEP)- biopotent stem cell
3. Megakayrocyte- Committed progenitor cell (MKP): monopotent stem cell
4. Megakaryoblast: large cell, non-lobed, endomitosis (chromosomes replicate but cell does not divide), under the influences of cytokines (thrombopoietin)
5. Megakaryocyte: Large cell, complex, multi-loved nucleus, scattered azurophilic granules, Karyokinesis (division of nucleus), Cytokinesis
6. Platlets
Thrombopoietin (TPO)
- regulator of platelet production
- produced primarily by liver and also kidneys and bone marrow
- prevents apoptosis of megakaryocytes (MKs)
- promotes MK maturation
- promotes proliferation of MKP
- synergistic affect with platelet agonists - promotes thrombosis
- acts on c-Mpl receptor (expressed on platelets, megakaryocytes and precursors)
Clinical Relevance of TPO: Thrombocythemia, Thrombocytosis, Thrombocytopenia
Liver Failure –> insufficient in producing TPO
- Thrombocythemia: inherited, activating mutations in TPO. Results in too many platelets, abnormal clotting.
- Thrombocytosis= inherited, too many platelets due to a secondary mechanism- not at platelet level of production
- Thrombocytopenia= bleeding disorder b/c not enough platelets
Leukopoiesis
= a form of hematopoiesis in which white blood cells (WBC, or leukocytes) are formed in bone marrow- formation of neutrophils, macrophages, eosinophil, basophils
- Granulocytes vs. Agranulocytes: based on the presence of granules: granules have secretory vesicles filled with cytotoxic enzymes and peptides released via degranulation
- Azurophilic (nonspecific) granules: filled with enzymes that function in phagocytosis - stains darkly
Granulocytes vs. Agranulocytes
- Granulocytes: have grainy cytoplasmic type of staining. Cells contain specific granules: neutrophils, eosinophils, basophils
- Agranulocytes: Cells without specific granules: Lymphocytes (T cells, B cells, NK cells), Monocytes/macrophages
Myeloid Lineage
- basophilic = blue = lots of ribosomes = + environment
- azurophilic= magenta = acidic
- Myeoblast: nucleus is round and uncondensed chomatin visible in nucleolus. Cytoplasm is granule free (As cell progresses, nucleus becomes indented, then segmented then chromatin increases in condensation.)
- Promyelocyte: Larger, has a large nucleus with uncondensed chromatin, and nucleoli. Primary granules (azurophilic) stain magenta. Cytoplasm is basophilic due to presence of rER (stains blue)
- Myelocyte: cell shrinks, basophilic cytopalasm contains granules - last stage capable of mitosis
- Metamyelocyte: smaller diameter, the bean-shaped nucleus contains some condensed chromasome, the specific granules outnumber primary
- Band Form: cell is smaller, Nucleus is U-Shaped
(don’t need to know the specifics of this card….)
Neutrophils
- Looks light pink with granules and a purple multilobed nucleus in U-shape
- Polymorphonuclear.
- Larger than erythrocytes.
- Nucleus has 2-4 lobes.
- Heterochromatin located at periphery.
- Cytoplasm lacks staining.
- most common leukocyte
- produced on demand and transitory manner
- phagocytic and function in eliminating bacteria and parasites
Eosinophil
- looks brighter pink with larger granules and a less dramatic u shaped 2 lobed nucleus
- Larger than erythrocytes,
- Nucleus is bi-lobed,
- heterochromatin are located at the periphery.
- Eosinophilic dark staining due to presence of azurophilic granules (crystalline proteins)
- cytoplasm contains large refractile specifi granules that appear bright red
- responsible for combating multicellular parasites and certain infections in vertebrates. Along with mast cells, they also control mechanisms associated with allergy and asthma.
Basophil
- looks purple/blue with no seen nucleus due to so many granules
- larger than erythrocytes
- lobed nucleus, usually obscured by intense basophilic staining due to azurophilic granules
- heterochromatin located at periphery
- active in allergy and hypersensitivity reactions, primary histamine producing cell type
Monocytes
- (not a granulocyte!) don’t stain for specific granules
- looks pale gray blue (basophilic), with a nucleus with a distinct indentation - only stains (azurophilic/blue)
- Mononuclear phagocytes
- Largest of WBC’s
- Cytoplasm: Golgi and centrioles located at nuclear indentation. Small dense azurophilic granules, SER and RER, mithcondria
- Lifespan: circulates in blood for 3 days, differentiates in local tissues into Macrophages or Osteoclasts.
Granulopoeisis (subtype of myelopoiesis) - production of neutrophils, eosinophils, and basophils
- Location: bone marrow. Final differentiation in connective tissue.
1. CMP (Common Myeloid Progenitor)
2. GMP (Granulocyte/Monocyte Progenitor)
3. Granuloycte progeinitors (neutrophil, eosinophil, basophil)
4. Myeloblast: large cell, spherical nucleus, small amount of granules
5. Promyelocyte: all azurophilic granules located here
6. Myelocyte (this is where they differentiate): - subtypes may be distinguishable due to production of specific granules
7. Metamyelocyte: specific granule production, nucleus expresses heterochromatin and indentations appear
7** Band Cell (neutrophils only)- Nucleus becomes elongated and horseshoe appears
8. Mature Granulocyte: nuclear lobes appear
9. Differentiation in connective tissue
IL-3
Interleukin 3= responsible for expansion of immature marrow progenitors into all types of mature hematopoietic cells
- produced by CD4 and T cells
GM-CSF
- granulocyte-macrophage Colony
- promotes maturation of bone marrow cells into dendritic cells (T/Bcells, Langerhans, etc.) and monocytes
- G-CSF produced at sites of infection to mobilize neutrophils from bone marrow
- clinical correlation: both used to recover from cancer chemotherapy and bone marrow transplantation
Lymphocytes
(Lympoid cells)
- Small Lymphocytes: include T and B cells: distinguishable by size- small lymphocytes are not larger than erythrocytes. 90% of lymphocytes, slightly indentened intensely stained nucleus, cytoplasm is a thin pale blue rim
- Large Lymphocytes: include NT cells: - same sized nucleus as small, but larger amount of cytoplastm. all blue.
- all are produced in bone marrow.. b cells mature in marrow, t cells in thymus and NK cells in tissues
B Cell
Small lymphocyte with variable lifespan
- antibody production
- matures in bone marrow
T cell
Small lymphocyte with long life span
- cell-mediated immunity
- matures in the thymus
Natural Killer Cell
Large Lymphocyte
- kidney shaped nucleus with large cytoplasmic granules
- functions in cell killing process
- matures in specific tissues
IL-7
Important in Lymphopoiesis
- stimulates expansion of immature B and T cells
- produced by stromal cells in many tissues
- clinical correlation: X-linked SCID: decrease of T cells and increase of B cells due to lack of IL-7 signals.
Granulocyte colony stimulating factor (G-CSF)
- target cell: neutrophils
Thrombopoietin (TPO)
target cells: megacaryocyte progenitors
