One of the most widely used marker combinations for chronic (mature) lymphocyte analysis is CD5 with CD19. Usually, CD5 is a T cell marker, and CD19 is a B cell marker. Normal B cells do not express CD5 but do express CD19. However, abnormal B cells (i.e., neoplastic B cells) can express CD5. Therefore, if the cell population expresses both markers, it is highly likely that the patient has a B cell neoplasm, such as chronic lymphocytic leukemia (CLL) or mantle cell lymphoma.
