SCYM Immunophenotyping 5 — Questions and Answers
Question 1: In immunophenotyping of chronic myelomonocytic leukemia (CMML), which monocyte subset ratio abnormality is diagnostically significant?
- Classical monocytes (CD14+/CD16-) >94% of total monocytes (Correct answer)
- Non-classical monocytes (CD14dim/CD16+) >50%
- CD56+ monocytes comprising >80% of the subset
- CD64-negative monocytes >75% of total
Correct answer: Classical monocytes (CD14+/CD16-) >94% of total monocytes
CMML is characterized by a predominance of classical monocytes (CD14+/CD16-) comprising >94% of all monocytes, distinguishing it from reactive monocytosis where non-classical monocytes increase.
Question 2: Which surface marker combination identifies regulatory T cells (Tregs) by flow cytometry?
- CD4+/CD25high/CD127low (Correct answer)
- CD8+/CD57+/CD16+
- CD4+/CD45RA+/CCR7+
- CD3-/CD56+/CD16+
Correct answer: CD4+/CD25high/CD127low
Regulatory T cells are identified as CD4+/CD25high/CD127low, with FOXP3 intracellular staining providing additional confirmation.
Question 3: When evaluating a CD34+ blast population in AML for megakaryoblastic lineage (AML-M7), which markers should be included in the panel?
- CD41, CD61, and CD42b (Correct answer)
- CD64, CD14, and CD11b
- CD19, CD22, and CD79a
- CD7, CD2, and cytoplasmic CD3
Correct answer: CD41, CD61, and CD42b
Megakaryoblastic differentiation is confirmed by expression of platelet glycoproteins CD41 (GPIIb), CD61 (GPIIIa), and CD42b (GPIbα).
Question 4: Which flow cytometric finding in a cerebrospinal fluid (CSF) specimen would best support leptomeningeal involvement by CLL?
- CD5+/CD19+/CD23+/dim sIg+ B cells with clonal light chain restriction (Correct answer)
- CD3+/CD4+ T cells with high CD25 expression
- CD34+/TdT+ lymphoblasts without B-cell markers
- CD38+/CD138+ plasma cells lacking CD19
Correct answer: CD5+/CD19+/CD23+/dim sIg+ B cells with clonal light chain restriction
Detection of clonal CD5+/CD19+/CD23+ B cells with dim surface immunoglobulin and light chain restriction in CSF confirms leptomeningeal CLL involvement.
Question 5: In post-transplant lymphoproliferative disorder (PTLD) immunophenotyping, which EBV-associated antigen can be detected by flow cytometry to support the diagnosis?
- CD30 upregulation on EBV-infected B cells
- EBV-LMP1 detected by intracellular flow staining (Correct answer)
- CD45 downregulation on infected cells
- CD7 loss as a marker of viral infection
Correct answer: EBV-LMP1 detected by intracellular flow staining
EBV latent membrane protein 1 (LMP1) can be detected by intracellular flow cytometry on infected B cells, supporting EBV-driven PTLD in immunosuppressed patients.
Question 6: Which immunophenotypic feature distinguishes reactive plasmacytosis from neoplastic plasma cells (multiple myeloma) in bone marrow flow cytometry?
- Neoplastic plasma cells lack CD19 and often gain CD56 (Correct answer)
- Reactive plasma cells express CD56 and lack CD38
- Neoplastic plasma cells retain CD20 and CD22
- Reactive plasma cells gain CD117 and lose CD138
Correct answer: Neoplastic plasma cells lack CD19 and often gain CD56
Neoplastic plasma cells in myeloma characteristically lose the normal B-cell marker CD19 and frequently aberrantly gain CD56, unlike reactive plasma cells which are CD19+/CD56-.
Question 7: When performing immunophenotyping to detect PNH clones on granulocytes, which reagents are preferred over CD59 alone for improved sensitivity?
- FLAER plus CD24 and CD16 (Correct answer)
- Anti-CD59 plus anti-CD55 only
- FLAER plus CD45 and CD15
- CD14 plus CD64 without FLAER
Correct answer: FLAER plus CD24 and CD16
The International Clinical Cytometry Society recommends FLAER (a fluorescent aerolysin that binds GPI anchors directly) combined with CD24 and CD16 on granulocytes for sensitive and specific PNH granulocyte clone detection.
SCYM Immunophenotyping 5
In immunophenotyping of chronic myelomonocytic leukemia (CMML), which monocyte subset ratio abnormality is diagnostically significant?