Improved detection of CD5 epitope in formalin-fixed paraffin-embedded sections of benign and neoplastic lymphoid tissues by using biotinylated tyramine enhancement after antigen retrieval.

To evaluate the effectiveness of the immunohistochemical staining of B- and T-cell lymphomas with Leu-1 (clone L17F12 CD5 antibody, Becton Dickinson, San Jose, Calif) in formalin-fixed paraffin-embedded sections, we stained 12 specimens reflecting cases of chronic lymphocytic leukemia/small lymphocytic lymphoma, 7 of mantle cell lymphoma, 13 of T-cell lymphomas, and 9 of various B-cell neoplasms that do not ordinarily express CD5, using a streptavidin-horseradish peroxidase method with biotinylated tyramine enhancement after antigen retrieval. We were able to detect CD5 reactivity of neoplastic cells in 9 (75%) of 12 cases of chronic lymphocytic leukemia, 6 (86%) of 7 cases of mantle cell lymphoma, and 13 (100%) of 13 of the T-cell lymphomas. B-cell neoplasms (9/9) not typically associated with CD5 expression showed no reactivity of tumor cells. We conclude that the Leu-1 (CD5) antibody, routinely used for cryopreserved tissues, is also effective in formalin-fixed paraffin-embedded sections using an antigen retrieval and streptavidin-horseradish peroxidase method with biotinylated tyramine.