Identification of a novel protein capable of interacting with the IL-3 receptor.
IL-3 has numerous functions in hematopoiesis yet its receptor has not been fully characterized. We have developed two mAb, 4G8 and 2F2, that markedly inhibited IL-3-dependent proliferation whereas only marginally affecting IL-2 or IL-4-induced proliferation. On Western blots, both antibodies identified the same protein, which varied in size from 115 to 145 kDa in six cell lines tested. The 4G8/2F2 Ag was detected at moderate density, on a wide variety of cells including IL-3-dependent cell lines and T lymphocytes. Radioligand binding studies revealed that 4G8, but not 2F2, could inhibit the binding of 125I-IL-3 to the high affinity IL-3R. These data suggest that the mAb 4G8 and 2F2 recognize different epitopes on the same Ag, and suggest furthermore that the inhibition of IL-3-dependent proliferation mediated by 2F2, in particular, does not occur via inhibition of ligand binding. Neither antibody showed an enhanced level of fluorescent staining of Cos 7 cells transfected with the low affinity IL-3R cDNA. In addition, 4G8 did not inhibit IL-3 binding to L cells transfected with the cloned IL-3R or IL-4R despite the fact that 4G8 was expressed on these cells. These data suggest that the 4G8/2F2 Ag is a unique cell surface protein that can interact with the endogenous functional IL-3R.
Morel
P A
PA
Department of Medicine, University of Pittsburgh School of Medicine, PA.
Schreurs
J
J
Townsend
K
K
Gross
M
M
Chiller
J M
JM
Tweardy
D J
DJ
D000818:Animals; D000911:Antibodies, Monoclonal; D015153:Blotting, Western; D002460:Cell Line; D066298:In Vitro Techniques; D007376:Interleukin-2 / Q000378:metabolism; D007377:Interleukin-3 / Q000378:metabolism; D015847:Interleukin-4 / Q000378:metabolism; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000378:metabolism; D046911:Macromolecular Substances; D008407:Mast Cells / Q000378:metabolism; D008565:Membrane Proteins / Q000276:immunology / Q000502:physiology*; D051379:Mice; D008970:Molecular Weight; D015375:Receptors, Interleukin-2 / Q000378:metabolism; D016185:Receptors, Interleukin-3 / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D019948:Receptors, Interleukin-4; D011975:Receptors, Mitogen / Q000378:metabolism; D015398:Signal Transduction
D000911:Antibodies, Monoclonal; D007376:Interleukin-2; D007377:Interleukin-3; D046911:Macromolecular Substances; D008565:Membrane Proteins; D015375:Receptors, Interleukin-2; D016185:Receptors, Interleukin-3; D019948:Receptors, Interleukin-4; D011975:Receptors, Mitogen; D015847:Interleukin-4