Surrogate thrombopoietin.
The extracellular domain of human c-Mpl, the receptor for thrombopoietin (TPO), was expressed as a chimeric protein with the interleukin-2 receptor alpha chain on the surface of murine B cell-line B300-19. BALB/c mice were immunized with cells expressing the chimeric protein. The IgG purified from the resulting immune serum immunoprecipitated human c-Mpl. The immune IgG supported proliferation of both stable transfectant Ba/F3 cells expressing whole c-Mpl molecules (c-Mpl-Ba/F3 No. 9) and UT7/TPO cells bearing naturally occurring c-Mpl, whereas it did not support the growth of the untransfected parental Ba/F3 cells. Cell growth was induced using 3 to 100 microg/ml of immune IgG in a dose-dependent manner, but this induction was decreased at doses higher than 100 microg/ml. Non-immune IgG did not affect cell growth of c-Mpl-Ba/F3 No. 9 cells. Although the Fab fragment of immune IgG also immunoprecipitated c-Mpl, it did not support cell growth at concentrations as high as 180 microg/ml, implying that the bivalent binding of receptors by antibodies is essential for cell proliferation. These results suggest that antibodies against human c-Mpl stimulate the proliferation and differentiation of megakaryocytes by their bivalent binding to receptors like TPO.
Abe
M
M
Institute for Drug Discovery Research, Yamanouchi Pharmaceutical, Tsukuba, Ibaraki, Japan. abe_m@yamanouchi.co.jp
Yano
S
S
Sakaba
N
N
Kitamura
K
K
Urasaki
T
T
Nakada
S
S
Kawasaki
H
H
Morimoto
C
C
Masuho
Y
Y
D000818:Animals; D002455:Cell Division; D002460:Cell Line; D015870:Gene Expression; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D018121:Receptors, Cytokine; D011971:Receptors, Immunologic / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D053628:Receptors, Thrombopoietin; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology; D013926:Thrombopoietin / Q000378:metabolism*
D007074:Immunoglobulin G; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D011971:Receptors, Immunologic; D053628:Receptors, Thrombopoietin; D011993:Recombinant Fusion Proteins; C082218:MPL protein, human; D013926:Thrombopoietin