HEMA 311: Hematopoiesis

Hematopoiesis

Continuous, regulated process of blood cell production that includes cell renewal, proliferation, differentiation, and maturation

Hematopoietic System

Serves as a functional model to study stem cell function

Hematopoietic Stem Cell (HSC)

Capable of self-renewal and directed differentiation into all required cell lineages

Mesoblastic Phase

• When: 19th - 20th day of gestation

• Where: blood islands of yolk sac (mesoderm)

• What:

  1. Primitive erythroblasts

  2. Angioblasts

  3. Embryonic HGBs (Gower I, Gower II, and Portland HGB)

8th - 12th Week

What stage of gestation does the production of cells lasts in mesoblastic phase?

Angioblasts

Product in mesoblastic phase that forms the blood vessels

3rd Month

The production of embryonic hemoglobin stops because blood islands disappear after what stage of gestation?

Aorta-Gonad-Mesonephros (AGM) Region

Where cells of mesodermal origin migrate to

• Give rise to definitive erythroblasts and later into HSCs

Yolk Sac Phase

Other term for mesoblastic phase

Gower-I

Globin chains:

• 2 epsilon

• 2 zeta

Remember: 1 = EZ

Gower-II

Globin chains:

• 2 alpha

• 2 epsilon

Remember: 2 = TAE

Portland HGB

Globin chains:

• 2 zeta

• 2 gamma

Remember: ZiGa si Portland

Hepatic Phase

• When: 5th - 7th week of gestation

• Where: Fetal liver

• What:

  1. Development of lymphoid organs

  2. Definitive erythroblasts

  3. Granulocytes and Megakaryocytes

  4. Lymphocytes

  5. Monocytes

  6. Fetal hemoglobin (Hgb F) and Adult hemoglobin (Hgb A)

Intravascular (within blood vessel)

Is hematopoiesis during the mesoblastic phase intravascular or extravascular?

Extravascular (outside of blood vessel)

Is hematopoiesis during the hepatic phase intravascular or extravascular?

6th Month

Hematopoiesis in the hepatic phase gradually declines after what stage of gestation?

Thymus

• First fully developed organ in the fetus

• T Cell production

Fetal Hemoglobin (Hgb F).

Predominant hemoglobin during the hepatic phase.

• upto 1 year old

Spleen

Aside from the kidney, which organ produces B cells?

100 days

Minimum life span of RBCs

140 days

Maximum life span of RBCs

2nd Week

At what point in fetal development does the liver stop producing blood cells but remains capable of reactivation during severe blood loss?

Fetal Hemoglobin (Hgb F)

Globin chains:

• 2 alpha

• 2 gamma

Remember: F-A-G

120 days

Average life span of RBCs

Adult Hemoglobin (Hgb A1)

Globin chains:

• 2 alpha

• 2 beta

Adult Hemoglobin (Hgb A2)

Globin chains:

• 2 alpha

• 2 delta

Adult Hemoglobin (Hgb A)

Hemoglobin during the hepatic phase that is only in detectable levels

Erythropoiesis

What type of blood cell production is the mesoblastic phase confined to?

Extramedullary Hematopoiesis

Hematopoiesis that occurs outside the bone marrow

Medullary Phase

• When: starts at 24th week of gestation (4th - 5th month of fetal development) until death

• Where: Medulla / Bone Marrow Cavity (inner part of the bone)

• What:

  1. HSCs and Mesenchymal cells migrate into the medulla

Granulocytes and Megakaryocytes

Blood cells formed during the hepatic phase in the 3rd month of gestation

Lymphocytes

Blood cells formed during the hepatic phase in the 4th month of gestation

Monocytes

Blood cells formed during the hepatic phase in the 5th month of gestation

Mesenchymal Cells

A type of embryonic tissue that differentiate into structural elements to support developing blood cells

Myeloid Phase

Myeloid activity is apparent during this stage

• Other term for medullary phase

3:1 - 4:1

Normal myeloid-to-erythroid (M:E) ratio in adults

Infection

6:1 (M:E ratio)

Leukemia

25:1 (M:E ratio)

Myeloid Hyperplasia

20:1 (M:E ratio)

Myeloid Hypoplasia

3:20 (M:E ratio)

Erythroid Hyperplasia

1:20 (M:E ratio)

Erythroid Hypoplasia

5:1 (M:E ratio)

Adult Hemoglobin (Hgb A).

Predominant Hgb after 1 year old.

Detectable Cytokines in Medullary Phase

1. Erythropoietin (EPO)

2. Granulocyte colony-stimulating factor (G-CSF)

3. Granulocyte-Macrophage colony-stimulating factor (GM-CSF)

Cytokines

What group of signaling proteins primarily regulates HSC’s production of blood cells during the medullary phase?

Lymphocytes.

What blood cell is mostly produced through extramedullary hematopoiesis?.

Primary Lymphoid Tissue

Where T and B lymphocytes are derived

• Bone marrow

• Thymus

Secondary Lymphoid Tissue

Where lymphoid cells respond to foreign Ag

• Spleen

• Lymph nodes

• Mucosa-associated lymphoid tissue (MALT)

• Gut-associated lymphoid tissue (GALT)

Infancy and Early Childhood

• 80 - 90% active marrow

• Stage of life where all the bones in the body contain primarily red marrow

5 - 7 Yrs Old

• 60% active marrow

• Stage of life where retrogression occurs (active marrow > adipocytes)

Adult

• 40% active marrow

• Stage of life where active marrow is restricted to the:

  • Sternum

  • Vertebrae

  • Scapulae

  • Pelvis / Iliac crest

  • Ribs

  • Skull

  • Proximal portion of long bones

Marrow Cellularity

Ratio of red marrow to yellow marrow; usually decreases w/ age

Normocellular

Marrow has 30 - 70% HSCs

Hypocellular

Marrow has less than 30% HSCs

Hypercellular

Marrow has more than 70% HSCs

Aplastic

Marrow has few or no HSCs

Sternum

Main source of blood cell production in adults

Iliac Crest

Safest, most accessible site for bone marrow aspiration or biopsy

• Iron 52

• Iron 59

• Technetium 99m-colloid

Dyes for identification of active hematopoietic tissue

Direct Aspirate Smears

• Wedge-shaped smear

• Avoid crushing the spicules

Anticoagulated Aspirate Smears

• K3 EDTA

Crush Smears

• Places additional glass slide directly over the specimen

Imprints

• Closely replicate aspirate morphology

Concentrate Smears

• Narrow-bore glass or a plastic tube such as “Wintrobe HCT tube”

Histologic Sections

• 10% Formalin

• Zenker glacial acetic acid

• B5 fixative

Marrow Smear Dyes

1. Wright’s stain

2. Wright-Giemsa stain

Stromal Cells

Cells in the bone marrow that secrete a semifluid extracellular matrix that serves to anchor developing hematopoietic cells in the bone cavity

• Regulation of hematopoietic stem and progenitor cell survival and differentiation

Endothelial Cells

A stromal cell that regulates the flow of particles entering and leaving hematopoietic spaces

Adipocytes

A stromal cell that secretes steroids and regulates the volume of the marrow

Macrophages

A phagocytic stromal cell that secretes cytokines for regulation of hematopoiesis (together with LYMPHs)

Osteoblasts

Bone-forming stromal cells

Osteoclasts

Bone-resorbing stromal cells

Reticular Adventitial Cells

A stromal cell that forms a supporting lattice for the developing hematopoietic cells

Fibroblasts

Other term for reticular adventitial cells

Red Marrow

Composed of hematopoietic cells arranged in extravascular cords

Erythroblasts (in red marrow)

Develops in small clusters; located adjacent to the outer surfaces of vascular sinuses

Megakaryocytes (in red marrow)

Facilitates the release of platelets into the lumen of the sinus; located adjacent to the walls of vascular sinuses

Immature (myeloid) Granulocytic Cells (in red marrow)

Located deep w/n the cords but moves closer to the vascular sinuses as they mature along their differentiation pathway

Hematopoietic Microenvironment

Plays an important role in nurturing and protecting HSCs and regulating a balance among their quiescence, self-renewal, and differentiation

Niches

Other term for hematopoietic microenvironment

Spleen.

Largest lymphoid organ in the body.

350 mL

In a healthy individual, how much blood does the spleen contain?

Adenitis

Infection of the lymph node

6 Billion

• 2.5 B (erythrocytes)

• 2.5 B (platelets)

• 1 B (granulocytes)

How many blood cells per kg of body weight are produced each day?

Hematopoietic Stem Cell (HSC)

Differentiates into progenitor cells committed to either lymphoid or myeloid lineages when stimulated by cytokines

Monophyletic Theory

Suggests that all blood cells are derived from a single progenitor stem cell

Pluripotent Hematopoietic Stem Cell (PHSC)

The single progenitor stem cell in monophyletic theory is called a ________

Polyphyletic Theory

Suggests that each of the blood cell lineages is derived from its own unique stem cell

Apoptosis

Aside from self-renewal and differentiation, what is a possible fate for HSCs?

Stochastic Model of Hematopoiesis

Hematopoiesis is a random process whereby the HSC randomly commits to self-renewal or differentiation

Instructive Model of Hematopoiesis

The microenvironment in the bone marrow determines whether the HSC will self-renew or differentiate

Common Myeloid / Lymphoid Progenitor

Differentiates into lineage-specific progenitors (colony-forming units or CFU)

Lineage-specific Progenitors

Give rise to morphologically recognizable lineage-specific precursor cells

Megakaryocytes

Largest cells found in the bone marrow

Precursor Cells

Blast forms that undergo maturation

Differentiation

HSC > Common Myeloid / Lymphoid progenitors

Maturation

Precursor (blast) cells > mature cells

CFU-GEMM

Cell line:

• Granulocyte

• Erythrocyte

• Megakaryocyte

• Monocyte

CFU-E

Cell line:

• Erythrocyte

CFU-Meg

Cell line:

• Megakaryocyte