Which lymphocyte marker is commonly absent in follicular lymphoma?

• A. CD20
• B. CD45
• C. CD5
• D. CD19

Answer: (C)

In follicular lymphoma, the commonly absent lymphocyte marker is CD5. Follicular lymphoma is a type of non-Hodgkin lymphoma that typically arises from follicle center B-cells. These malignant B-cells often express certain surface markers characteristic of B-lymphocytes.

CD5 is generally expressed on T-lymphocytes and a subset of B-lymphocytes, particularly in chronic lymphocytic leukemia (CLL) and some other B-cell neoplasms. However, in follicular lymphoma, the neoplastic cells usually do not express CD5. This is relevant in differentiating follicular lymphoma from other B-cell lymphomas, particularly those that may express CD5, such as mantle cell lymphoma or CLL.

The other markers mentioned—CD20, CD45, and CD19—are typically present in follicular lymphoma. CD20 is a classic B-cell marker that is commonly expressed in B-cell neoplasms, including follicular lymphoma. CD45 is a pan-leukocyte marker, present on most leukocytes, and is also found in follicular lymphoma. CD19 is another B-cell marker commonly expressed throughout B-cell development and continues to be present in malignant B-cell populations.

The absence of CD