Blood, Vol. 95 No. 2 (January 15), 2000:
pp. 461-469
Identification of the soluble granulocyte-macrophage colony
stimulating factor receptor protein in vivo
Farzana Sayani,
Felix A. Montero-Julian,
Valerie Ranchin,
Jay M. Prevost,
Sophie Flavetta,
Weibin Zhu,
Richard C. Woodman,
Herve Brailly, and
Christopher B. Brown
From the Alberta Bone Marrow/Stem Cell Transplant Program and
Division of Hematology, Departments of Medicine and Oncology,
University of Calgary, Calgary, Alberta, Canada, and Immunotech, a
Beckman-Coulter Company, Marseille, France.
On the basis of the finding of alternatively spliced mRNAs, the
-subunit of the receptor for GM-CSF is thought to exist in both a
membrane spanning (tmGMR) and a soluble form (solGMR). However,
only limited data has been available to support that the solGMR
protein product exists in vivo. We hypothesized that hematopoietic
cells bearing tmGMR would have the potential to also produce
solGMR. To test this hypothesis we examined media conditioned by
candidate cells using functional, biochemical, and immunologic means.
Three human leukemic cell lines that express tmGMR (HL60, U937,
THP1) were shown to secrete GM-CSF binding activity and a
solGMR-specific band by Western blot, whereas a tmGMR-negative
cell line (K562) did not. By the same analyses, leukapheresis products
collected for autologous and allogeneic stem cell transplants and media
conditioned by freshly isolated human neutrophils also contained
solGMR. The solGMR protein in vivo displayed the same
dissociation constant (Kd = 2-5 nmol) as that of recombinant
solGMR. A human solGMR ELISA was developed that confirmed the
presence of solGMR in supernatant conditioned by the
tmGMR-positive leukemic cell lines, hematopoietic progenitor cells,
and neutrophils. Furthermore, the ELISA demonstrated a steady state
level of solGMR in normal human plasma (36 ± 17 pmol) and
provided data suggesting that plasma solGMR levels can be elevated
in acute myeloid leukemias.
