High and Low Affinity Receptors for Human Interleukin for DA Cells / Leukemia Inhibitory Factor on Human Cells

Radioiodinated recombinant human interleukin DA (HILDA)/leukemia inhibitory factor (LIF) purified from conditioned medium of Chinese hamster ovary transfected cells enabled the identification of specific receptor sites on a variety of human cell types. Using low concentrations (up to 500 PM) of the ligand iodinated at a high specific radioactivity, high affinity receptors (equilibrium dissociation constant & in the range of 30-100 PM) were first demonstrated. They were expressed at low levels by human peripheral blood monocytes but not by lymphocytes, NK cells, granulocytes, and platelets. The myelomonocytic cell line THPl as well as the T lymphoma cell line HSB2 and the lymphoblastoid B cell line DAB were also receptor-negative. In contrast, most of the non-lymphoid tumoral cell lines tested, including melanomas, neuroblastomas, and carcinomas, expressed high affinity HILDA/LIF receptors at variable levels (I$,,,= from 20 to 600 sites/cell). The kinetics of HILDA/LIF high affinity binding to the choriocarcinoma JAR cell line were characterized at 4 “C with association and dissociation rate constants of kl = 2.2 lo9 M” min-’ and k-l = 0.0084 min”, respectively, corresponding to a steady-state dissociation constant kl/k-l= 3.8 p ~ . The subsequent use of higher concentrations of HILDA/LIF labeled at a lower specific radioactivity enabled the identification of a low affinity component on several cell lines (& in the range of 1-4 nM; B,,, from 1,000 to 6,000 sites/cell). On JAR cells, this low affinity component was characterized by association and dissociation rate constants at 4 “C of k , = 7.3 lo7 M” min” and k-, = 0.19 min”, respectively (k-,/kl = 2.6 nM). Affinity cross-linking of HILDA/LIF to JAR cells showed two cross-linked species under both reducing and nonreducing conditions corresponding to receptor species of 120 and 250 kDa, respectively. Whereas both bands had similar intensities under high affinity conditions, the higher band predominated under low affinity conditions. Our data suggest that the 250-kDa chain could constitute the low affinity binding component whereas the association of both 250and 120-Da