Blood and BM Path Chapters 2 and 3 - Normal Bone Marrow

Question 1

Immunophenotype Tree of Hematopoietic Cells

Answer 1

Myeloid progenitors acquire cKit positivity

Lymphoid progenitors acquire TdT positivity.

Question 2

EPO signaling

Answer 2

Epo-EpoR binding activates JAK2. JAK2 activation results in STAT3/5 recruitment and formation of a STAT3/5 dimer formation.

STAT3/5 dimer translocates to the nucleus to act as a transcription factor.

SHP-1 antagonizes further JAK2 signaling by recognizing active receptors via its SH2 domain and dephosphorylating JAK2. SHP-1 is a tumor suppressor gene.

Question 3

“Normoblast”

Answer 3

A normal-looking erythroblast

Question 4

Erythroblasts and MHCI

Answer 4

At the same time erythroblasts accumulate hemoglobin, they lose MHCI expression.

Think of them as being inversely proportional.

Question 5

Types of megakaryocyte (increasing maturity)

Answer 5

• Megakaryoblast (Type I) - smaller, similar to myeloblasts but very high N/C ratio.
• Promegakaryocyte (Type II)
• Granular megakaryocyte (Type III) – functional megakaryocytes that produce platelets.
• “Bare” nucleus – senescent/dying megakrayocyte.

Question 6

Emperipolesis

Answer 6

• Describes the presence and movement of one cell within the cytoplasm of another cell.
  
  • The “engulfed” cell can leave the “engulfing” cell and appear unaltered by the interaction
• Commonly seen with megakaryocytes
  
  • May engulf neutrophils, eosinophils, lymphocytes, red cells, blasts, etc
• Different from phagocytosis – this is not a mechanism of killing/recycling

Question 7

“Primary” ganules

Answer 7

aka Azurophilic ganules

Called “primary” because they are present in multiple granulocyte lineages and are easily visible on light microscopy (due to presence of myeloperoxidase). However, their exact contents depend upon the cell type.

This is as opposed to “specific” ganules, which are different between different granulocytes.

Question 8

Neutrophil granule development as a tool to determine precursor stage

Answer 8

Primary (azurophilic) granules develop at the promyelocyte stage

Secondary granules develop at the myelocyte stage

Tertiary granules develop at the metamyelocyte stage

Question 9

Eosinophil crystal inclusions

Answer 9

Not visible on light microscopy, but clearly visible on TEM

Eosinophil cytoplasm contains crystals of major basic protein, which is a helpful identifying feature.

Not to be confused with the extracellular Charcot-Leyden crystals seen in the case of large-scale eosinophil degranulation (those are composed of galectin-10).

Question 10

NK cell markers

Answer 10

• Committed NK cell progenitors:
  
  • CD161⁺
  • CD56^- CD16^-
• Mature NK cells
  
  • CD56⁺
  • CD16⁺ or CD16^- (two subsets)

Question 11

Answer 11

Osteoblasts

Don’t forget that these are in the bone marrow too!

Question 12

Answer 12

Osteoclasts

Don’t forget these are in bone marrow too!

Question 13

Lineages on flow cytometry

Answer 13

• Precursors: CD34⁺CD45^lowSCC^low
• Erythropoietic precursors: CD45^-SSC^low
• Granulocytic precursors and mature granulocytes: CD45^dimSCC^variable
• Monocytes: CD45^highSCC^high
• Mature lymphocytes: CD45^highSCC^low

Question 14

A good starting plot for immunophenotyping

Answer 14

CD45 by SCC

Question 15

Bone marrow “zones”

Answer 15

“Endosteal” is more commonly called “paratrabecular”