Not a B cell marker
**Core Concept**
The question is testing the student's knowledge of cell surface markers associated with B cells, a crucial aspect of immunology in medical education. B cells, or B lymphocytes, are a type of white blood cell that plays a central role in the adaptive immune system.
**Why the Correct Answer is Right**
B cells express a variety of surface markers, including CD19, CD20, CD21, and CD23. These markers are used to identify and isolate B cells for various diagnostic and therapeutic purposes. The correct answer is a marker that is not typically associated with B cells, but rather with another type of immune cell or cell type.
**Why Each Wrong Option is Incorrect**
**Option A:** CD19 is a B cell-specific marker that is expressed on the surface of mature B cells. It is a crucial component of the B cell receptor complex and is involved in B cell development and activation.
**Option B:** CD20 is another B cell-specific marker that is expressed on the surface of mature B cells, but not on plasma cells or pro-B cells. It is a target for certain therapeutic antibodies, such as rituximab.
**Option C:** CD23 is a low-affinity receptor for IgE and is expressed on the surface of mature B cells, but also on other cell types, including eosinophils and mast cells. While it is associated with B cells, it is not as specific as CD19 or CD20.
**Clinical Pearl / High-Yield Fact**
The CD20 marker is a key target for therapeutic antibodies, such as rituximab, which are used to treat certain autoimmune diseases, including rheumatoid arthritis and lupus.
**Correct Answer:** C. CD23 is a marker associated with eosinophils, mast cells, and mature B cells, but is not as specific to B cells as CD19 or CD20.