Immunohistochemical detection of CD5 with monoclonal antibody 4C7 on paraffin sections

CD5 is useful for the classification of low-grade B-cell lymphomas, because it is aberrantly expressed in B-cell chronic lymphocytic leukemias/small lymphocytic lymphomas (B-CLLs/SLLs) and mantle cell lymphomas (MCLs), but not in the other well-described low-grade B-cell lymphomas. Therefore, we tested the utility of monoclonal antibody (MAb) 4C7 to detect CD5 on paraffin sections of 22 cases with low-grade B-cell lymphomas and 4 cases with high-grade B-cell lymphomas and compared the results with CD5 detection by analysis of fresh tissue with a fluorescent-activated cell sorting (FACS). After heat-induced epitope retrieval we could detect CD5 on paraffin sections in all MCLs and B-CLLs/SLLs, identical to the results of flow cytometry. Eleven of 12 cases that showed no CD5 expression by FACS analysis were also negative on paraffin sections. In only one case of a presumed blastoid MCL, CD5 was detectable by immunohistochemistry but not by FACS analysis. We conclude that MAb 4C7 against CD5 is a useful paraffin-reactive marker, especially to correctly identify MCLs on paraffin sections.