Division of Hematology/Oncology, Carmen and Ann Adams Department of Pediatrics, Children's Hospital of Michigan, Detroit, Michigan.
Hematology/Oncology Flow Cytometry Laboratory, Children's Hospital of Michigan, Carmen and Ann Adams Department of Pediatrics, Detroit, Michigan.
Cytometry B Clin Cytom. 2018 May;94(3):477-483. doi: 10.1002/cyto.b.21613. Epub 2018 Jan 17.
Flow cytometric intracellular myeloperoxidase (MPO) staining of leukemic blasts is a useful tool in diagnosis of leukemia subtype. Interpretation of high MPO-positivity can be a diagnostic challenge in B-lineage acute lymphoblastic leukemia (B-ALL). While very few such cases have been reported, high MPO positive B-ALL cases without additional myeloid antigen positivity are suspect and require further investigation.
Three pediatric cases of B-ALL with strong MPO staining (clone 8E6; Invitrogen) at diagnosis and three others with negative MPO staining were studied by flow cytometry and immunohistochemistry. In-vitro drug cytotoxicity, oxidative stress generation, and immunophenotyping using other MPO clones were performed to further investigate MPO presence.
Expectedly, normal myeloid cells in all six samples were positive and mature lymphocytes negative for MPO staining. However, MPO monoclonal antibody (mAb) obtained from clones other than Invitrogen and other myeloid-specific mAbs gave negative results suggesting false positivity of the initial MPO staining. Immunohistochemistry for MPO was also negative on all six cases tested. Furthermore, in-vitro vincristine cytotoxicity was greater in leukemic cells from MPO false-positive cases compared with MPO-negative B-ALL samples, demonstrating indirect lack of MPO activity. Moreover, drug treatment did not lead to generation of reactive oxidative species, also reflective of lack of significant MPO presence.
The cause of false-positive MPO staining remains unknown in these three cases; a cross reactivity could be the culprit. Caution should be given to similar phenomena and detailed investigation may contribute to the understanding of altered protein expression in such outlier cases. © 2017 International Clinical Cytometry Society.
流式细胞术检测白血病细胞内髓过氧化物酶（MPO）染色是诊断白血病亚型的有用工具。在 B 细胞急性淋巴细胞白血病（B-ALL）中，高 MPO 阳性的解读可能是一个诊断挑战。虽然很少有这样的病例报告，但没有其他髓系抗原阳性的高 MPO 阳性 B-ALL 病例是可疑的，需要进一步调查。
我们研究了 3 例诊断时 MPO 染色强阳性（Invitrogen 公司的克隆 8E6）的儿童 B-ALL 病例和另外 3 例 MPO 染色阴性的病例，采用流式细胞术和免疫组化法进行研究。为了进一步研究 MPO 的存在，我们进行了体外药物细胞毒性、氧化应激生成和使用其他 MPO 克隆的免疫表型分析。
不出所料，所有 6 个样本中的正常髓系细胞均为 MPO 染色阳性，成熟淋巴细胞为 MPO 染色阴性。然而，来自 Invitrogen 以外的克隆的 MPO 单克隆抗体（mAb）和其他髓系特异性 mAb 均给出阴性结果，提示初始 MPO 染色为假阳性。对所有 6 例检测的组织进行 MPO 免疫组化染色也为阴性。此外，MPO 假阳性病例的白血病细胞中长春新碱细胞毒性比 MPO 阴性 B-ALL 样本更大，表明 MPO 活性间接缺乏。此外，药物治疗未导致活性氧物质的生成，这也反映了 MPO 不存在的情况。
在这 3 例病例中，导致 MPO 染色假阳性的原因尚不清楚；可能是一种交叉反应。对于类似的现象应谨慎，并进行详细调查，这有助于理解此类异常病例中蛋白质表达的改变。© 2017 国际临床细胞化学学会。
