Differential human interferon α receptor expression on proliferating and non‐proliferating cells

The expression of interferon‐α (IFN‐α) receptors was studied on a variety of human cells, using monoiodinated IFN‐α₂ probes. Steady‐state binding at 4°C revealed a single class of non‐interacting IFN receptor on peripheral blood lymphocytes, and tonsillar B lymphocytes, which are both known to be G₀/G₁ resting cell populations. The binding affinity of this class of receptor was found to be on the order of 5 × 10⁻¹⁰ M, expressed as an apparent dissociation constant (K_d). However, cells proliferating either in culture or in vivo were found to express a heterogeneity in IFN‐α₂ binding. Such binding could be objectively resolved (by a version of the LIGAND program of P. Munson) into a two‐site receptor model. Hill plots of binding to proliferating cells indicated a negative cooperativity in the interaction of IFN and receptor. The high‐affinity component, expressed on proliferating cells, typically exhibits a K_d of (1–10) × 10⁻¹¹ M, while the lower‐affinity component indicates a K_d of (1–10) × 10⁻⁹ M. Furthermore, the low‐affinity component is apparently expressed on the order of 10–200 times the copy number, per cell, of the high‐affinity site. Affinity‐labeling experiments revealed that, in addition to the 140–160‐kDa IFN‐binding complex reported by others, both the proliferating and non‐proliferating cell populations possess a novel IFN‐binding component of 60 kDa.