While a directly proportional relationship between serum haptoglobin (Hp) levels and acute myeloid leukemia (AML) has been documented, the exact source of this elevated haptoglobin remains in dispute. Furthermore, no reported studies thus far have analyzed haptoglobin-targeted immunohistochemistry as a potential diagnostic tool for AML. In this study, we examined Hp expression in patients with AML. Previously collected blood samples were obtained, with informed consent, during routine diagnostic blood studies from twenty-one patients with AML (13 males, 8 females; age range 4–73 years). Cytospin samples were prepared, and immunohistochemistry was performed using a polyclonal anti-haptoglobin antibody. Total RNA was extracted from 19 AML patient samples as well as from a K562 leukemic cell line for the RT-PCR assay. Cytospin specimens derived from all twenty-one patients with confirmed AML showed consistent anti-haptoglobin staining of blast cells in a granular, cytoplasmic pattern. The K562 cell line, used as a positive control, stained in a similar fashion to the patient samples. Immunohistochemical co-labeling of blasts was achieved with the AML anti-podocalyxin marker in conjunction with the anti-haptoglobin antibody. All of the AML blasts as well as the K562 cells expressed Hp by the RT-PCR assay. The ratio index (RI) of Hp band density against β-actin serving as an internal control was used to compare the expression level among the AML cases. The RIs ranged from 0.89 to 0.02, indicating different Hp transcription levels among the AMLs. We conclude that haptoglobin is produced by AML blasts and stored within the cytoplasm. This may partly explain the increased serum level of haptoglobin observed in AML patients. Furthermore, immunohistochemistry consistently detects these intra-blastic haptoglobin stores, suggesting a potential for a novel diagnostic tool for AML.
Disclosure:Research Funding: University of Missouri-Kansas City School of Medicine.