Which pair correctly identifies a plasma cell immunophenotype?

Which pair correctly identifies a plasma cell immunophenotype?

• A. CD19 and CD20
• B. CD45 and CD3
• C. CD38 and CD138
• D. CD56 and CD7

Answer: (C)

Plasma cells have a distinctive surface marker profile, most notably bright CD38 expression and CD138 (syndecan-1) on their surface. These two markers together are the standard way to identify plasma cells by flow cytometry in marrow or blood samples. CD38 is highly expressed on plasma cells, and CD138 helps confirm plasma cell lineage. In contrast, CD19 and CD20 are B-cell markers that are downregulated as cells differentiate into plasma cells, so their presence points to earlier B-cell stages rather than mature plasma cells. CD3 is a T-cell marker, and CD56 can be variably expressed on some plasma cell neoplasms, but CD7 is a T/NK cell marker—these do not define plasma cells as reliably as CD38 and CD138.

Plasma cells have a distinctive surface marker profile, most notably bright CD38 expression and CD138 (syndecan-1) on their surface. These two markers together are the standard way to identify plasma cells by flow cytometry in marrow or blood samples. CD38 is highly expressed on plasma cells, and CD138 helps confirm plasma cell lineage. In contrast, CD19 and CD20 are B-cell markers that are downregulated as cells differentiate into plasma cells, so their presence points to earlier B-cell stages rather than mature plasma cells. CD3 is a T-cell marker, and CD56 can be variably expressed on some plasma cell neoplasms, but CD7 is a T/NK cell marker—these do not define plasma cells as reliably as CD38 and CD138.