Characterization of a New Monoclonal Antibody Against PAX5/BASP in 1525 Paraffin-embedded Human and Animal Tissue Samples

Introduction: We describe the newly generated DAK-PAX5 monoclonal antibody raised against a fixation-resistant epitope of the human PAX5/BSAP molecule. Materials and Methods: Following Western-blot, absorption, and chess-board titration tests, and optimization of antigen-retrieval and detection methods, DAK-Pax5 was used in parallel with a reference antibody (clone 24) on tissue microarrays (TMAs) constructed from normal human and animal tissues and from hematologic and nonhematologic human malignancies. Such TMAs were also tested with an anti-PAX2 antibody. Results: DAK-Pax5 reacted with normal human and animal B-cells and with 460/473 B-cell non-Hodgkin lymphomas (BNHLs). All plasmacytomas/plasmablastic tumors (n = 13) and T/NK-cell neoplasms (n = 264) turned out consistently negative as did acute myelogenous leukaemias (n = 19) except 2 carrying t(8;21). Positivity was found in 6/6 and 155/169 lymphocyte predominant and classical HLs, respectively, although the staining intensity varied through cases. Among 521 nonhematologic malignancies, DAK-Pax5 reacted with 22/399 carcinomas (4/11 neuroendocrine, 2/4 Merkel-cell, 4/21 prostatic, 1/11 urothelial, 1/26 renal, 2/12 cervical squamous-cell, 3/13 ovarian, and 5/75 colonic). When compared with clone 24, DAK-Pax5 produced a stronger positivity in most if not all B-NHLs and HLs. No cross-reactivity with the anti-PAX2 antibody was recorded. Discussion: DAK-Pax5 represents a new reliable tool for diagnostics and research.