In chronic lymphocytic leukemia, which immunophenotypic marker combination is most characteristic: CD5+, CD19+, CD23+, and surface immunoglobulin expression?

Question

Accepted Answer

C. B-cell CLL with co-expression of T-cell marker CD5. ## Immunophenotype of CLL

**Key Point:** CLL is characterized by a unique immunophenotype: CD5+ CD19+ CD23+ B cells with dim surface immunoglobulin and CD79b expression.

### Diagnostic Immunophenotype

| Marker | CLL | Mantle Cell | Marginal Zone |
|--------|-----|-------------|---------------|
| CD5 | + | + | − |
| CD19 | + | + | + |
| CD23 | + | − | − |
| Surface Ig | Dim | Bright | Bright |
| FMC7 | − | + | + |

### Clinical Significance
- **CD5+ B cells:** Unusual co-expression of T-cell marker on B cells is the hallmark
- **CD23+ status:** Distinguishes CLL from mantle cell lymphoma (CD23−)
- **Dim surface Ig:** Indicates monoclonal B-cell population with restricted light chain (κ or λ)

**High-Yield:** The CD5+ CD19+ CD23+ immunophenotype is sufficient for CLL diagnosis in the appropriate clinical context; no bone marrow biopsy required if peripheral blood shows >5,000 clonal B lymphocytes/μL.

**Mnemonic:** **"CLL is CD5 CD19 CD23"** — remember all three are positive in CLL, unlike other B-cell lymphomas.

**Clinical Pearl:** CD5+CD23− B-cell lymphocytosis suggests mantle cell lymphoma or marginal zone lymphoma, not CLL.

Answer

A. T-cell prolymphocytic leukemia

Answer

B. Marginal zone lymphoma

Answer

D. Mantle cell lymphoma

In chronic lymphocytic leukemia, which immunophenotypic marker combination is most characteristic: CD5+, CD19+, CD23+, and surface immunoglobulin expression?

Explanation

Immunophenotype of CLL

Diagnostic Immunophenotype

Clinical Significance

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Marker	CLL	Mantle Cell	Marginal Zone
CD5	+	+	−
CD19	+	+	+
CD23	+	−	−
Surface Ig	Dim	Bright	Bright
FMC7	−	+	+