Immunophenotypic Profile of Chronic Lymphocytic Leukemia
Chronic lymphocytic leukemia (CLL) is commonly positive for CD5, CD19, CD20, and CD23, making option D the correct answer. 1
Characteristic Immunophenotype of CLL
CLL cells have a distinctive immunophenotypic profile that helps differentiate it from other lymphoproliferative disorders:
- Core markers: CD5+, CD19+, CD20+ (dim), CD23+ 1
- Additional markers: CD43+/-, CD200+, CD79b (dim/low) 1, 2
- Surface immunoglobulin: Characteristically dim 1, 3
- Light chain restriction: Either kappa or lambda 1
Key Distinguishing Features
- CD20 expression is typically dim compared to normal B cells 1, 2
- Surface immunoglobulin levels are characteristically low 1
- CD5 positivity (a T-cell antigen aberrantly expressed on CLL B-cells) 3
Ruling Out Other Options
Option A (prolymphocytes >55%): Incorrect. In CLL, prolymphocytes may be present but must not exceed 55% of lymphocytes. When prolymphocytes exceed 55%, the diagnosis shifts to prolymphocytic leukemia, not CLL. 1
Option B (positive TRAP stains): Incorrect. Tartrate-resistant acid phosphatase (TRAP) staining is typically associated with hairy cell leukemia, not CLL. 1
Option C (diagnosis only by bone marrow examination): Incorrect. CLL diagnosis is usually possible by immunophenotyping of peripheral blood alone. Bone marrow biopsy is generally not required for diagnosis. 1
Diagnostic Criteria for CLL
For a definitive diagnosis of CLL, the following criteria must be met:
- Presence of ≥5000 monoclonal B lymphocytes/μL in peripheral blood 1
- Clonality confirmed by flow cytometry 1
- Characteristic morphology: small, mature-appearing lymphocytes with narrow cytoplasmic border and dense nucleus 1
Differential Diagnosis
It's important to distinguish CLL from other CD5+ B-cell lymphoproliferative disorders:
- Mantle cell lymphoma: Also CD5+, but typically CD23-, with t(11;14) translocation and cyclin D1 expression 1
- Marginal zone lymphoma: Typically CD5-, CD23-, CD43 low 1
- Small lymphocytic lymphoma (SLL): Same immunophenotype as CLL but <5000 B lymphocytes/μL with lymphadenopathy/splenomegaly 1
Clinical Implications
The immunophenotypic profile of CLL not only confirms diagnosis but also has prognostic implications:
- Flow cytometry is essential for establishing diagnosis and monitoring disease 2
- Additional genetic testing (FISH for del(11q), del(13q), trisomy 12, del(17p)) provides important prognostic information 1
- IGHV mutation status should be determined before first treatment 4
The characteristic immunophenotype of CD5+, CD19+, CD20+ (dim), and CD23+ is a cornerstone for CLL diagnosis and helps distinguish it from other lymphoproliferative disorders.