All of the following are true concerning hematopoietic stem cells ...

[Collmarie]

All of the following are true concerning hematopoietic stem cells except:
 
  a. They express both CD34 and CD117 (c-kit).
  b. They lose some antigens as they mature.
  c. They express both CD4 and CD34.
  d. They gain lineage-specific antigens as they mature.

Question 2

A patient has a white cell count of 12.6 x 109/L, hematocrit of 28, and platelet count of 27 x 109/L.
 
  Examination of a Wright-stained blood film reveals that almost all of the white cells in peripheral blood are blasts; the bone marrow is hypercellular with very little fat and is packed with blasts. Flow cytometry is performed on the peripheral blood cells, and a large cluster of cells is present that mark with CD20 and have monoclonal k light chains present on their surface. This patient has a:
 
  a. Myeloid leukemia
  b. Mature B-cell malignancy
  c. Reactive B-cell hyperplasia
  d. Mature T-cell malignancy

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Answer to Question 1

ANS: C
CD4 is a marker of T cells, not hematopoietic stem cells (HSCs). HSCs express both CD34 and CD117 (c-kit). As they mature, some antigens are lost while lineage-specific antigens are gained.

Answer to Question 2

ANS: B
Mature B lymphocytes express CD20 and either k or l light chains on their surface. In a B-cell reactive process, a mixture of k and l light chain positivity will be observed. The expression of only one light chain on the surface of a population of B cells is called monoclonality and is indicative of a phenotypically mature B-cell malignancy.

[Collmarie]

TYSM

[bblaney]

Excellent