One of the most widely used marker combinations for chronic (mature) cellular 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 (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 lymphoid leukemia (CLL) or mantle cell lymphoma.