SCYM Immunophenotyping 2 — Questions and Answers
Question 1: Which CD marker is characteristically expressed on plasma cells and used to distinguish them from mature B cells in flow cytometry?
- CD19
- CD38 (Correct answer)
- CD20
- CD22
Correct answer: CD38
CD38 is highly expressed on plasma cells, whereas mature B cells typically downregulate CD38 and retain CD19/CD20.
Question 2: In immunophenotyping of T-cell lymphomas, loss of which antigen is most commonly used as evidence of aberrant T-cell populations?
- CD5
- CD3
- CD7 (Correct answer)
- CD2
Correct answer: CD7
CD7 is the most frequently lost pan-T-cell antigen in T-cell lymphomas, making its absence a useful aberrancy marker.
Question 3: Which combination of markers best identifies natural killer (NK) cells by flow cytometry?
- CD3+/CD16+/CD56+
- CD3-/CD16+/CD56+ (Correct answer)
- CD3+/CD56-/CD16-
- CD3-/CD4+/CD56+
Correct answer: CD3-/CD16+/CD56+
NK cells are CD3-negative but express CD16 and CD56, distinguishing them from NKT cells which are CD3-positive.
Question 4: TdT expression in flow cytometry is most useful for identifying which cell population?
- Mature plasma cells
- Granulocyte precursors
- Lymphoblasts (Correct answer)
- Monocytes
Correct answer: Lymphoblasts
Terminal deoxynucleotidyl transferase (TdT) is a nuclear enzyme expressed in immature lymphoid precursors (lymphoblasts) and is a key marker for ALL.
Question 5: In a patient with suspected chronic lymphocytic leukemia (CLL), which immunophenotypic feature would argue AGAINST a CLL diagnosis?
- CD5 co-expression with CD19
- Bright surface immunoglobulin expression (Correct answer)
- CD23 positivity
- CD200 positivity
Correct answer: Bright surface immunoglobulin expression
CLL cells characteristically show dim surface immunoglobulin; bright sIg expression is atypical and suggests mantle cell lymphoma or other B-cell disorders.
Question 6: Which marker combination is most characteristic of hairy cell leukemia (HCL) on flow cytometry?
- CD103+/CD11c+/CD25+/CD123+ (Correct answer)
- CD5+/CD23+/CD200+
- CD10+/CD19+/BCL6+
- CD38+/CD138+/CD45dim
Correct answer: CD103+/CD11c+/CD25+/CD123+
HCL classically co-expresses CD103, CD11c, CD25, and CD123, forming a highly specific immunophenotypic signature.
Question 7: When performing immunophenotyping for paroxysmal nocturnal hemoglobinuria (PNH), which marker directly detects the GPI-anchored protein deficiency?
- CD59 on red blood cells (Correct answer)
- CD3 on T cells
- HLA-DR on monocytes
- CD45 on granulocytes
Correct answer: CD59 on red blood cells
CD59 is a GPI-anchored complement regulatory protein; its absence on erythrocytes by flow cytometry is a direct measure of PNH clone size.
SCYM Immunophenotyping 2
Which CD marker is characteristically expressed on plasma cells and used to distinguish them from mature B cells in flow cytometry?